inode.c

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/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card ([email protected])
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *  ([email protected])
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/fs.h>
#include <linux/time.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/namei.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include <linux/workqueue.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "truncate.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
                  struct ext4_inode_info *ei)
{
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    __u16 csum_lo;
    __u16 csum_hi = 0;
    __u32 csum;

    csum_lo = raw->i_checksum_lo;
    raw->i_checksum_lo = 0;
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
        EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
        csum_hi = raw->i_checksum_hi;
        raw->i_checksum_hi = 0;
    }

    csum = ext4_chksum(sbi, ei->i_csum_seed, (__u8 *)raw,
               EXT4_INODE_SIZE(inode->i_sb));

    raw->i_checksum_lo = csum_lo;
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
        EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
        raw->i_checksum_hi = csum_hi;

    return csum;
}

static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw,
                  struct ext4_inode_info *ei)
{
    __u32 provided, calculated;

    if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
        cpu_to_le32(EXT4_OS_LINUX) ||
        !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
        return 1;

    provided = le16_to_cpu(raw->i_checksum_lo);
    calculated = ext4_inode_csum(inode, raw, ei);
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
        EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
        provided |= ((__u32)le16_to_cpu(raw->i_checksum_hi)) << 16;
    else
        calculated &= 0xFFFF;

    return provided == calculated;
}

static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
                struct ext4_inode_info *ei)
{
    __u32 csum;

    if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
        cpu_to_le32(EXT4_OS_LINUX) ||
        !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
        return;

    csum = ext4_inode_csum(inode, raw, ei);
    raw->i_checksum_lo = cpu_to_le16(csum & 0xFFFF);
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
        EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
        raw->i_checksum_hi = cpu_to_le16(csum >> 16);
}

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                          loff_t new_size)
{
    trace_ext4_begin_ordered_truncate(inode, new_size);
    /*
     * If jinode is zero, then we never opened the file for
     * writing, so there's no need to call
     * jbd2_journal_begin_ordered_truncate() since there's no
     * outstanding writes we need to flush.
     */
    if (!EXT4_I(inode)->jinode)
        return 0;
    return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
                           EXT4_I(inode)->jinode,
                           new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);
static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create);
static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode);
static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
static int __ext4_journalled_writepage(struct page *page, unsigned int len);
static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
static int ext4_discard_partial_page_buffers_no_lock(handle_t *handle,
        struct inode *inode, struct page *page, loff_t from,
        loff_t length, int flags);

/*
 * Test whether an inode is a fast symlink.
 */
static int ext4_inode_is_fast_symlink(struct inode *inode)
{
    int ea_blocks = EXT4_I(inode)->i_file_acl ?
        (inode->i_sb->s_blocksize >> 9) : 0;

    return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
                 int nblocks)
{
    int ret;

    /*
     * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
     * moment, get_block can be called only for blocks inside i_size since
     * page cache has been already dropped and writes are blocked by
     * i_mutex. So we can safely drop the i_data_sem here.
     */
    BUG_ON(EXT4_JOURNAL(inode) == NULL);
    jbd_debug(2, "restarting handle %p\n", handle);
    up_write(&EXT4_I(inode)->i_data_sem);
    ret = ext4_journal_restart(handle, nblocks);
    down_write(&EXT4_I(inode)->i_data_sem);
    ext4_discard_preallocations(inode);

    return ret;
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_evict_inode(struct inode *inode)
{
    handle_t *handle;
    int err;

    trace_ext4_evict_inode(inode);

    ext4_ioend_wait(inode);

    if (inode->i_nlink) {
        /*
         * When journalling data dirty buffers are tracked only in the
         * journal. So although mm thinks everything is clean and
         * ready for reaping the inode might still have some pages to
         * write in the running transaction or waiting to be
         * checkpointed. Thus calling jbd2_journal_invalidatepage()
         * (via truncate_inode_pages()) to discard these buffers can
         * cause data loss. Also even if we did not discard these
         * buffers, we would have no way to find them after the inode
         * is reaped and thus user could see stale data if he tries to
         * read them before the transaction is checkpointed. So be
         * careful and force everything to disk here... We use
         * ei->i_datasync_tid to store the newest transaction
         * containing inode's data.
         *
         * Note that directories do not have this problem because they
         * don't use page cache.
         */
        if (ext4_should_journal_data(inode) &&
            (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
            journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
            tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;

            jbd2_log_start_commit(journal, commit_tid);
            jbd2_log_wait_commit(journal, commit_tid);
            filemap_write_and_wait(&inode->i_data);
        }
        truncate_inode_pages(&inode->i_data, 0);
        goto no_delete;
    }

    if (!is_bad_inode(inode))
        dquot_initialize(inode);

    if (ext4_should_order_data(inode))
        ext4_begin_ordered_truncate(inode, 0);
    truncate_inode_pages(&inode->i_data, 0);

    if (is_bad_inode(inode))
        goto no_delete;

    /*
     * Protect us against freezing - iput() caller didn't have to have any
     * protection against it
     */
    sb_start_intwrite(inode->i_sb);
    handle = ext4_journal_start(inode, ext4_blocks_for_truncate(inode)+3);
    if (IS_ERR(handle)) {
        ext4_std_error(inode->i_sb, PTR_ERR(handle));
        /*
         * If we're going to skip the normal cleanup, we still need to
         * make sure that the in-core orphan linked list is properly
         * cleaned up.
         */
        ext4_orphan_del(NULL, inode);
        sb_end_intwrite(inode->i_sb);
        goto no_delete;
    }

    if (IS_SYNC(inode))
        ext4_handle_sync(handle);
    inode->i_size = 0;
    err = ext4_mark_inode_dirty(handle, inode);
    if (err) {
        ext4_warning(inode->i_sb,
                 "couldn't mark inode dirty (err %d)", err);
        goto stop_handle;
    }
    if (inode->i_blocks)
        ext4_truncate(inode);

    /*
     * ext4_ext_truncate() doesn't reserve any slop when it
     * restarts journal transactions; therefore there may not be
     * enough credits left in the handle to remove the inode from
     * the orphan list and set the dtime field.
     */
    if (!ext4_handle_has_enough_credits(handle, 3)) {
        err = ext4_journal_extend(handle, 3);
        if (err > 0)
            err = ext4_journal_restart(handle, 3);
        if (err != 0) {
            ext4_warning(inode->i_sb,
                     "couldn't extend journal (err %d)", err);
        stop_handle:
            ext4_journal_stop(handle);
            ext4_orphan_del(NULL, inode);
            sb_end_intwrite(inode->i_sb);
            goto no_delete;
        }
    }

    /*
     * Kill off the orphan record which ext4_truncate created.
     * AKPM: I think this can be inside the above `if'.
     * Note that ext4_orphan_del() has to be able to cope with the
     * deletion of a non-existent orphan - this is because we don't
     * know if ext4_truncate() actually created an orphan record.
     * (Well, we could do this if we need to, but heck - it works)
     */
    ext4_orphan_del(handle, inode);
    EXT4_I(inode)->i_dtime  = get_seconds();

    /*
     * One subtle ordering requirement: if anything has gone wrong
     * (transaction abort, IO errors, whatever), then we can still
     * do these next steps (the fs will already have been marked as
     * having errors), but we can't free the inode if the mark_dirty
     * fails.
     */
    if (ext4_mark_inode_dirty(handle, inode))
        /* If that failed, just do the required in-core inode clear. */
        ext4_clear_inode(inode);
    else
        ext4_free_inode(handle, inode);
    ext4_journal_stop(handle);
    sb_end_intwrite(inode->i_sb);
    return;
no_delete:
    ext4_clear_inode(inode);    /* We must guarantee clearing of inode... */
}

#ifdef CONFIG_QUOTA
qsize_t *ext4_get_reserved_space(struct inode *inode)
{
    return &EXT4_I(inode)->i_reserved_quota;
}
#endif

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate a block located at @lblock
 */
static int ext4_calc_metadata_amount(struct inode *inode, ext4_lblk_t lblock)
{
    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
        return ext4_ext_calc_metadata_amount(inode, lblock);

    return ext4_ind_calc_metadata_amount(inode, lblock);
}

/*
 * Called with i_data_sem down, which is important since we can call
 * ext4_discard_preallocations() from here.
 */
void ext4_da_update_reserve_space(struct inode *inode,
                    int used, int quota_claim)
{
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    struct ext4_inode_info *ei = EXT4_I(inode);

    spin_lock(&ei->i_block_reservation_lock);
    trace_ext4_da_update_reserve_space(inode, used, quota_claim);
    if (unlikely(used > ei->i_reserved_data_blocks)) {
        ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, used %d "
             "with only %d reserved data blocks",
             __func__, inode->i_ino, used,
             ei->i_reserved_data_blocks);
        WARN_ON(1);
        used = ei->i_reserved_data_blocks;
    }

    if (unlikely(ei->i_allocated_meta_blocks > ei->i_reserved_meta_blocks)) {
        ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, allocated %d "
             "with only %d reserved metadata blocks\n", __func__,
             inode->i_ino, ei->i_allocated_meta_blocks,
             ei->i_reserved_meta_blocks);
        WARN_ON(1);
        ei->i_allocated_meta_blocks = ei->i_reserved_meta_blocks;
    }

    /* Update per-inode reservations */
    ei->i_reserved_data_blocks -= used;
    ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;
    percpu_counter_sub(&sbi->s_dirtyclusters_counter,
               used + ei->i_allocated_meta_blocks);
    ei->i_allocated_meta_blocks = 0;

    if (ei->i_reserved_data_blocks == 0) {
        /*
         * We can release all of the reserved metadata blocks
         * only when we have written all of the delayed
         * allocation blocks.
         */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                   ei->i_reserved_meta_blocks);
        ei->i_reserved_meta_blocks = 0;
        ei->i_da_metadata_calc_len = 0;
    }
    spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

    /* Update quota subsystem for data blocks */
    if (quota_claim)
        dquot_claim_block(inode, EXT4_C2B(sbi, used));
    else {
        /*
         * We did fallocate with an offset that is already delayed
         * allocated. So on delayed allocated writeback we should
         * not re-claim the quota for fallocated blocks.
         */
        dquot_release_reservation_block(inode, EXT4_C2B(sbi, used));
    }

    /*
     * If we have done all the pending block allocations and if
     * there aren't any writers on the inode, we can discard the
     * inode's preallocations.
     */
    if ((ei->i_reserved_data_blocks == 0) &&
        (atomic_read(&inode->i_writecount) == 0))
        ext4_discard_preallocations(inode);
}

static int __check_block_validity(struct inode *inode, const char *func,
                unsigned int line,
                struct ext4_map_blocks *map)
{
    if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), map->m_pblk,
                   map->m_len)) {
        ext4_error_inode(inode, func, line, map->m_pblk,
                 "lblock %lu mapped to illegal pblock "
                 "(length %d)", (unsigned long) map->m_lblk,
                 map->m_len);
        return -EIO;
    }
    return 0;
}

#define check_block_validity(inode, map)    \
    __check_block_validity((inode), __func__, __LINE__, (map))

/*
 * Return the number of contiguous dirty pages in a given inode
 * starting at page frame idx.
 */
static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
                    unsigned int max_pages)
{
    struct address_space *mapping = inode->i_mapping;
    pgoff_t index;
    struct pagevec pvec;
    pgoff_t num = 0;
    int i, nr_pages, done = 0;

    if (max_pages == 0)
        return 0;
    pagevec_init(&pvec, 0);
    while (!done) {
        index = idx;
        nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
                          PAGECACHE_TAG_DIRTY,
                          (pgoff_t)PAGEVEC_SIZE);
        if (nr_pages == 0)
            break;
        for (i = 0; i < nr_pages; i++) {
            struct page *page = pvec.pages[i];
            struct buffer_head *bh, *head;

            lock_page(page);
            if (unlikely(page->mapping != mapping) ||
                !PageDirty(page) ||
                PageWriteback(page) ||
                page->index != idx) {
                done = 1;
                unlock_page(page);
                break;
            }
            if (page_has_buffers(page)) {
                bh = head = page_buffers(page);
                do {
                    if (!buffer_delay(bh) &&
                        !buffer_unwritten(bh))
                        done = 1;
                    bh = bh->b_this_page;
                } while (!done && (bh != head));
            }
            unlock_page(page);
            if (done)
                break;
            idx++;
            num++;
            if (num >= max_pages) {
                done = 1;
                break;
            }
        }
        pagevec_release(&pvec);
    }
    return num;
}

/*
 * Sets the BH_Da_Mapped bit on the buffer heads corresponding to the given map.
 */
static void set_buffers_da_mapped(struct inode *inode,
                   struct ext4_map_blocks *map)
{
    struct address_space *mapping = inode->i_mapping;
    struct pagevec pvec;
    int i, nr_pages;
    pgoff_t index, end;

    index = map->m_lblk >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
    end = (map->m_lblk + map->m_len - 1) >>
        (PAGE_CACHE_SHIFT - inode->i_blkbits);

    pagevec_init(&pvec, 0);
    while (index <= end) {
        nr_pages = pagevec_lookup(&pvec, mapping, index,
                      min(end - index + 1,
                          (pgoff_t)PAGEVEC_SIZE));
        if (nr_pages == 0)
            break;
        for (i = 0; i < nr_pages; i++) {
            struct page *page = pvec.pages[i];
            struct buffer_head *bh, *head;

            if (unlikely(page->mapping != mapping) ||
                !PageDirty(page))
                break;

            if (page_has_buffers(page)) {
                bh = head = page_buffers(page);
                do {
                    set_buffer_da_mapped(bh);
                    bh = bh->b_this_page;
                } while (bh != head);
            }
            index++;
        }
        pagevec_release(&pvec);
    }
}

/*
 * The ext4_map_blocks() function tries to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_map_blocks(),
 * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocate.
 * if create==0 and the blocks are pre-allocated and uninitialized block,
 * the result buffer head is unmapped. If the create ==1, it will make sure
 * the buffer head is mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that case, buffer head is unmapped
 *
 * It returns the error in case of allocation failure.
 */
int ext4_map_blocks(handle_t *handle, struct inode *inode,
            struct ext4_map_blocks *map, int flags)
{
    int retval;

    map->m_flags = 0;
    ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
          "logical block %lu\n", inode->i_ino, flags, map->m_len,
          (unsigned long) map->m_lblk);
    /*
     * Try to see if we can get the block without requesting a new
     * file system block.
     */
    if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
        down_read((&EXT4_I(inode)->i_data_sem));
    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
        retval = ext4_ext_map_blocks(handle, inode, map, flags &
                         EXT4_GET_BLOCKS_KEEP_SIZE);
    } else {
        retval = ext4_ind_map_blocks(handle, inode, map, flags &
                         EXT4_GET_BLOCKS_KEEP_SIZE);
    }
    if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
        up_read((&EXT4_I(inode)->i_data_sem));

    if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
        int ret = check_block_validity(inode, map);
        if (ret != 0)
            return ret;
    }

    /* If it is only a block(s) look up */
    if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
        return retval;

    /*
     * Returns if the blocks have already allocated
     *
     * Note that if blocks have been preallocated
     * ext4_ext_get_block() returns the create = 0
     * with buffer head unmapped.
     */
    if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
        return retval;

    /*
     * When we call get_blocks without the create flag, the
     * BH_Unwritten flag could have gotten set if the blocks
     * requested were part of a uninitialized extent.  We need to
     * clear this flag now that we are committed to convert all or
     * part of the uninitialized extent to be an initialized
     * extent.  This is because we need to avoid the combination
     * of BH_Unwritten and BH_Mapped flags being simultaneously
     * set on the buffer_head.
     */
    map->m_flags &= ~EXT4_MAP_UNWRITTEN;

    /*
     * New blocks allocate and/or writing to uninitialized extent
     * will possibly result in updating i_data, so we take
     * the write lock of i_data_sem, and call get_blocks()
     * with create == 1 flag.
     */
    down_write((&EXT4_I(inode)->i_data_sem));

    /*
     * if the caller is from delayed allocation writeout path
     * we have already reserved fs blocks for allocation
     * let the underlying get_block() function know to
     * avoid double accounting
     */
    if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
        ext4_set_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);
    /*
     * We need to check for EXT4 here because migrate
     * could have changed the inode type in between
     */
    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
        retval = ext4_ext_map_blocks(handle, inode, map, flags);
    } else {
        retval = ext4_ind_map_blocks(handle, inode, map, flags);

        if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
            /*
             * We allocated new blocks which will result in
             * i_data's format changing.  Force the migrate
             * to fail by clearing migrate flags
             */
            ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
        }

        /*
         * Update reserved blocks/metadata blocks after successful
         * block allocation which had been deferred till now. We don't
         * support fallocate for non extent files. So we can update
         * reserve space here.
         */
        if ((retval > 0) &&
            (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
            ext4_da_update_reserve_space(inode, retval, 1);
    }
    if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
        ext4_clear_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);

        /* If we have successfully mapped the delayed allocated blocks,
         * set the BH_Da_Mapped bit on them. Its important to do this
         * under the protection of i_data_sem.
         */
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
            set_buffers_da_mapped(inode, map);
    }

    up_write((&EXT4_I(inode)->i_data_sem));
    if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
        int ret = check_block_validity(inode, map);
        if (ret != 0)
            return ret;
    }
    return retval;
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

static int _ext4_get_block(struct inode *inode, sector_t iblock,
               struct buffer_head *bh, int flags)
{
    handle_t *handle = ext4_journal_current_handle();
    struct ext4_map_blocks map;
    int ret = 0, started = 0;
    int dio_credits;

    map.m_lblk = iblock;
    map.m_len = bh->b_size >> inode->i_blkbits;

    if (flags && !handle) {
        /* Direct IO write... */
        if (map.m_len > DIO_MAX_BLOCKS)
            map.m_len = DIO_MAX_BLOCKS;
        dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
        handle = ext4_journal_start(inode, dio_credits);
        if (IS_ERR(handle)) {
            ret = PTR_ERR(handle);
            return ret;
        }
        started = 1;
    }

    ret = ext4_map_blocks(handle, inode, &map, flags);
    if (ret > 0) {
        map_bh(bh, inode->i_sb, map.m_pblk);
        bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
        bh->b_size = inode->i_sb->s_blocksize * map.m_len;
        ret = 0;
    }
    if (started)
        ext4_journal_stop(handle);
    return ret;
}

int ext4_get_block(struct inode *inode, sector_t iblock,
           struct buffer_head *bh, int create)
{
    return _ext4_get_block(inode, iblock, bh,
                   create ? EXT4_GET_BLOCKS_CREATE : 0);
}

/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                ext4_lblk_t block, int create, int *errp)
{
    struct ext4_map_blocks map;
    struct buffer_head *bh;
    int fatal = 0, err;

    J_ASSERT(handle != NULL || create == 0);

    map.m_lblk = block;
    map.m_len = 1;
    err = ext4_map_blocks(handle, inode, &map,
                  create ? EXT4_GET_BLOCKS_CREATE : 0);

    /* ensure we send some value back into *errp */
    *errp = 0;

    if (err < 0)
        *errp = err;
    if (err <= 0)
        return NULL;

    bh = sb_getblk(inode->i_sb, map.m_pblk);
    if (!bh) {
        *errp = -EIO;
        return NULL;
    }
    if (map.m_flags & EXT4_MAP_NEW) {
        J_ASSERT(create != 0);
        J_ASSERT(handle != NULL);

        /*
         * Now that we do not always journal data, we should
         * keep in mind whether this should always journal the
         * new buffer as metadata.  For now, regular file
         * writes use ext4_get_block instead, so it's not a
         * problem.
         */
        lock_buffer(bh);
        BUFFER_TRACE(bh, "call get_create_access");
        fatal = ext4_journal_get_create_access(handle, bh);
        if (!fatal && !buffer_uptodate(bh)) {
            memset(bh->b_data, 0, inode->i_sb->s_blocksize);
            set_buffer_uptodate(bh);
        }
        unlock_buffer(bh);
        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, inode, bh);
        if (!fatal)
            fatal = err;
    } else {
        BUFFER_TRACE(bh, "not a new buffer");
    }
    if (fatal) {
        *errp = fatal;
        brelse(bh);
        bh = NULL;
    }
    return bh;
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                   ext4_lblk_t block, int create, int *err)
{
    struct buffer_head *bh;

    bh = ext4_getblk(handle, inode, block, create, err);
    if (!bh)
        return bh;
    if (buffer_uptodate(bh))
        return bh;
    ll_rw_block(READ | REQ_META | REQ_PRIO, 1, &bh);
    wait_on_buffer(bh);
    if (buffer_uptodate(bh))
        return bh;
    put_bh(bh);
    *err = -EIO;
    return NULL;
}

static int walk_page_buffers(handle_t *handle,
                 struct buffer_head *head,
                 unsigned from,
                 unsigned to,
                 int *partial,
                 int (*fn)(handle_t *handle,
                       struct buffer_head *bh))
{
    struct buffer_head *bh;
    unsigned block_start, block_end;
    unsigned blocksize = head->b_size;
    int err, ret = 0;
    struct buffer_head *next;

    for (bh = head, block_start = 0;
         ret == 0 && (bh != head || !block_start);
         block_start = block_end, bh = next) {
        next = bh->b_this_page;
        block_end = block_start + blocksize;
        if (block_end <= from || block_start >= to) {
            if (partial && !buffer_uptodate(bh))
                *partial = 1;
            continue;
        }
        err = (*fn)(handle, bh);
        if (!ret)
            ret = err;
    }
    return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage() ->
 * block_write_full_page(). In that case, we *know* that ext4_writepage()
 * has generated enough buffer credits to do the whole page.  So we won't
 * block on the journal in that case, which is good, because the caller may
 * be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
static int do_journal_get_write_access(handle_t *handle,
                       struct buffer_head *bh)
{
    int dirty = buffer_dirty(bh);
    int ret;

    if (!buffer_mapped(bh) || buffer_freed(bh))
        return 0;
    /*
     * __block_write_begin() could have dirtied some buffers. Clean
     * the dirty bit as jbd2_journal_get_write_access() could complain
     * otherwise about fs integrity issues. Setting of the dirty bit
     * by __block_write_begin() isn't a real problem here as we clear
     * the bit before releasing a page lock and thus writeback cannot
     * ever write the buffer.
     */
    if (dirty)
        clear_buffer_dirty(bh);
    ret = ext4_journal_get_write_access(handle, bh);
    if (!ret && dirty)
        ret = ext4_handle_dirty_metadata(handle, NULL, bh);
    return ret;
}

static int ext4_get_block_write(struct inode *inode, sector_t iblock,
           struct buffer_head *bh_result, int create);
static int ext4_write_begin(struct file *file, struct address_space *mapping,
                loff_t pos, unsigned len, unsigned flags,
                struct page **pagep, void **fsdata)
{
    struct inode *inode = mapping->host;
    int ret, needed_blocks;
    handle_t *handle;
    int retries = 0;
    struct page *page;
    pgoff_t index;
    unsigned from, to;

    trace_ext4_write_begin(inode, pos, len, flags);
    /*
     * Reserve one block more for addition to orphan list in case
     * we allocate blocks but write fails for some reason
     */
    needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
    index = pos >> PAGE_CACHE_SHIFT;
    from = pos & (PAGE_CACHE_SIZE - 1);
    to = from + len;

retry:
    handle = ext4_journal_start(inode, needed_blocks);
    if (IS_ERR(handle)) {
        ret = PTR_ERR(handle);
        goto out;
    }

    /* We cannot recurse into the filesystem as the transaction is already
     * started */
    flags |= AOP_FLAG_NOFS;

    page = grab_cache_page_write_begin(mapping, index, flags);
    if (!page) {
        ext4_journal_stop(handle);
        ret = -ENOMEM;
        goto out;
    }
    *pagep = page;

    if (ext4_should_dioread_nolock(inode))
        ret = __block_write_begin(page, pos, len, ext4_get_block_write);
    else
        ret = __block_write_begin(page, pos, len, ext4_get_block);

    if (!ret && ext4_should_journal_data(inode)) {
        ret = walk_page_buffers(handle, page_buffers(page),
                from, to, NULL, do_journal_get_write_access);
    }

    if (ret) {
        unlock_page(page);
        page_cache_release(page);
        /*
         * __block_write_begin may have instantiated a few blocks
         * outside i_size.  Trim these off again. Don't need
         * i_size_read because we hold i_mutex.
         *
         * Add inode to orphan list in case we crash before
         * truncate finishes
         */
        if (pos + len > inode->i_size && ext4_can_truncate(inode))
            ext4_orphan_add(handle, inode);

        ext4_journal_stop(handle);
        if (pos + len > inode->i_size) {
            ext4_truncate_failed_write(inode);
            /*
             * If truncate failed early the inode might
             * still be on the orphan list; we need to
             * make sure the inode is removed from the
             * orphan list in that case.
             */
            if (inode->i_nlink)
                ext4_orphan_del(NULL, inode);
        }
    }

    if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
        goto retry;
out:
    return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
    if (!buffer_mapped(bh) || buffer_freed(bh))
        return 0;
    set_buffer_uptodate(bh);
    return ext4_handle_dirty_metadata(handle, NULL, bh);
}

static int ext4_generic_write_end(struct file *file,
                  struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned copied,
                  struct page *page, void *fsdata)
{
    int i_size_changed = 0;
    struct inode *inode = mapping->host;
    handle_t *handle = ext4_journal_current_handle();

    copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);

    /*
     * No need to use i_size_read() here, the i_size
     * cannot change under us because we hold i_mutex.
     *
     * But it's important to update i_size while still holding page lock:
     * page writeout could otherwise come in and zero beyond i_size.
     */
    if (pos + copied > inode->i_size) {
        i_size_write(inode, pos + copied);
        i_size_changed = 1;
    }

    if (pos + copied >  EXT4_I(inode)->i_disksize) {
        /* We need to mark inode dirty even if
         * new_i_size is less that inode->i_size
         * bu greater than i_disksize.(hint delalloc)
         */
        ext4_update_i_disksize(inode, (pos + copied));
        i_size_changed = 1;
    }
    unlock_page(page);
    page_cache_release(page);

    /*
     * Don't mark the inode dirty under page lock. First, it unnecessarily
     * makes the holding time of page lock longer. Second, it forces lock
     * ordering of page lock and transaction start for journaling
     * filesystems.
     */
    if (i_size_changed)
        ext4_mark_inode_dirty(handle, inode);

    return copied;
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_ordered_write_end(struct file *file,
                  struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned copied,
                  struct page *page, void *fsdata)
{
    handle_t *handle = ext4_journal_current_handle();
    struct inode *inode = mapping->host;
    int ret = 0, ret2;

    trace_ext4_ordered_write_end(inode, pos, len, copied);
    ret = ext4_jbd2_file_inode(handle, inode);

    if (ret == 0) {
        ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                            page, fsdata);
        copied = ret2;
        if (pos + len > inode->i_size && ext4_can_truncate(inode))
            /* if we have allocated more blocks and copied
             * less. We will have blocks allocated outside
             * inode->i_size. So truncate them
             */
            ext4_orphan_add(handle, inode);
        if (ret2 < 0)
            ret = ret2;
    } else {
        unlock_page(page);
        page_cache_release(page);
    }

    ret2 = ext4_journal_stop(handle);
    if (!ret)
        ret = ret2;

    if (pos + len > inode->i_size) {
        ext4_truncate_failed_write(inode);
        /*
         * If truncate failed early the inode might still be
         * on the orphan list; we need to make sure the inode
         * is removed from the orphan list in that case.
         */
        if (inode->i_nlink)
            ext4_orphan_del(NULL, inode);
    }


    return ret ? ret : copied;
}

static int ext4_writeback_write_end(struct file *file,
                    struct address_space *mapping,
                    loff_t pos, unsigned len, unsigned copied,
                    struct page *page, void *fsdata)
{
    handle_t *handle = ext4_journal_current_handle();
    struct inode *inode = mapping->host;
    int ret = 0, ret2;

    trace_ext4_writeback_write_end(inode, pos, len, copied);
    ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
                            page, fsdata);
    copied = ret2;
    if (pos + len > inode->i_size && ext4_can_truncate(inode))
        /* if we have allocated more blocks and copied
         * less. We will have blocks allocated outside
         * inode->i_size. So truncate them
         */
        ext4_orphan_add(handle, inode);

    if (ret2 < 0)
        ret = ret2;

    ret2 = ext4_journal_stop(handle);
    if (!ret)
        ret = ret2;

    if (pos + len > inode->i_size) {
        ext4_truncate_failed_write(inode);
        /*
         * If truncate failed early the inode might still be
         * on the orphan list; we need to make sure the inode
         * is removed from the orphan list in that case.
         */
        if (inode->i_nlink)
            ext4_orphan_del(NULL, inode);
    }

    return ret ? ret : copied;
}

static int ext4_journalled_write_end(struct file *file,
                     struct address_space *mapping,
                     loff_t pos, unsigned len, unsigned copied,
                     struct page *page, void *fsdata)
{
    handle_t *handle = ext4_journal_current_handle();
    struct inode *inode = mapping->host;
    int ret = 0, ret2;
    int partial = 0;
    unsigned from, to;
    loff_t new_i_size;

    trace_ext4_journalled_write_end(inode, pos, len, copied);
    from = pos & (PAGE_CACHE_SIZE - 1);
    to = from + len;

    BUG_ON(!ext4_handle_valid(handle));

    if (copied < len) {
        if (!PageUptodate(page))
            copied = 0;
        page_zero_new_buffers(page, from+copied, to);
    }

    ret = walk_page_buffers(handle, page_buffers(page), from,
                to, &partial, write_end_fn);
    if (!partial)
        SetPageUptodate(page);
    new_i_size = pos + copied;
    if (new_i_size > inode->i_size)
        i_size_write(inode, pos+copied);
    ext4_set_inode_state(inode, EXT4_STATE_JDATA);
    EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
    if (new_i_size > EXT4_I(inode)->i_disksize) {
        ext4_update_i_disksize(inode, new_i_size);
        ret2 = ext4_mark_inode_dirty(handle, inode);
        if (!ret)
            ret = ret2;
    }

    unlock_page(page);
    page_cache_release(page);
    if (pos + len > inode->i_size && ext4_can_truncate(inode))
        /* if we have allocated more blocks and copied
         * less. We will have blocks allocated outside
         * inode->i_size. So truncate them
         */
        ext4_orphan_add(handle, inode);

    ret2 = ext4_journal_stop(handle);
    if (!ret)
        ret = ret2;
    if (pos + len > inode->i_size) {
        ext4_truncate_failed_write(inode);
        /*
         * If truncate failed early the inode might still be
         * on the orphan list; we need to make sure the inode
         * is removed from the orphan list in that case.
         */
        if (inode->i_nlink)
            ext4_orphan_del(NULL, inode);
    }

    return ret ? ret : copied;
}

/*
 * Reserve a single cluster located at lblock
 */
static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
{
    int retries = 0;
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    struct ext4_inode_info *ei = EXT4_I(inode);
    unsigned int md_needed;
    int ret;
    ext4_lblk_t save_last_lblock;
    int save_len;

    /*
     * We will charge metadata quota at writeout time; this saves
     * us from metadata over-estimation, though we may go over by
     * a small amount in the end.  Here we just reserve for data.
     */
    ret = dquot_reserve_block(inode, EXT4_C2B(sbi, 1));
    if (ret)
        return ret;

    /*
     * recalculate the amount of metadata blocks to reserve
     * in order to allocate nrblocks
     * worse case is one extent per block
     */
repeat:
    spin_lock(&ei->i_block_reservation_lock);
    /*
     * ext4_calc_metadata_amount() has side effects, which we have
     * to be prepared undo if we fail to claim space.
     */
    save_len = ei->i_da_metadata_calc_len;
    save_last_lblock = ei->i_da_metadata_calc_last_lblock;
    md_needed = EXT4_NUM_B2C(sbi,
                 ext4_calc_metadata_amount(inode, lblock));
    trace_ext4_da_reserve_space(inode, md_needed);

    /*
     * We do still charge estimated metadata to the sb though;
     * we cannot afford to run out of free blocks.
     */
    if (ext4_claim_free_clusters(sbi, md_needed + 1, 0)) {
        ei->i_da_metadata_calc_len = save_len;
        ei->i_da_metadata_calc_last_lblock = save_last_lblock;
        spin_unlock(&ei->i_block_reservation_lock);
        if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
            yield();
            goto repeat;
        }
        dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
        return -ENOSPC;
    }
    ei->i_reserved_data_blocks++;
    ei->i_reserved_meta_blocks += md_needed;
    spin_unlock(&ei->i_block_reservation_lock);

    return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    struct ext4_inode_info *ei = EXT4_I(inode);

    if (!to_free)
        return;     /* Nothing to release, exit */

    spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

    trace_ext4_da_release_space(inode, to_free);
    if (unlikely(to_free > ei->i_reserved_data_blocks)) {
        /*
         * if there aren't enough reserved blocks, then the
         * counter is messed up somewhere.  Since this
         * function is called from invalidate page, it's
         * harmless to return without any action.
         */
        ext4_msg(inode->i_sb, KERN_NOTICE, "ext4_da_release_space: "
             "ino %lu, to_free %d with only %d reserved "
             "data blocks", inode->i_ino, to_free,
             ei->i_reserved_data_blocks);
        WARN_ON(1);
        to_free = ei->i_reserved_data_blocks;
    }
    ei->i_reserved_data_blocks -= to_free;

    if (ei->i_reserved_data_blocks == 0) {
        /*
         * We can release all of the reserved metadata blocks
         * only when we have written all of the delayed
         * allocation blocks.
         * Note that in case of bigalloc, i_reserved_meta_blocks,
         * i_reserved_data_blocks, etc. refer to number of clusters.
         */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                   ei->i_reserved_meta_blocks);
        ei->i_reserved_meta_blocks = 0;
        ei->i_da_metadata_calc_len = 0;
    }

    /* update fs dirty data blocks counter */
    percpu_counter_sub(&sbi->s_dirtyclusters_counter, to_free);

    spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

    dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
}

static void ext4_da_page_release_reservation(struct page *page,
                         unsigned long offset)
{
    int to_release = 0;
    struct buffer_head *head, *bh;
    unsigned int curr_off = 0;
    struct inode *inode = page->mapping->host;
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    int num_clusters;

    head = page_buffers(page);
    bh = head;
    do {
        unsigned int next_off = curr_off + bh->b_size;

        if ((offset <= curr_off) && (buffer_delay(bh))) {
            to_release++;
            clear_buffer_delay(bh);
            clear_buffer_da_mapped(bh);
        }
        curr_off = next_off;
    } while ((bh = bh->b_this_page) != head);

    /* If we have released all the blocks belonging to a cluster, then we
     * need to release the reserved space for that cluster. */
    num_clusters = EXT4_NUM_B2C(sbi, to_release);
    while (num_clusters > 0) {
        ext4_fsblk_t lblk;
        lblk = (page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits)) +
            ((num_clusters - 1) << sbi->s_cluster_bits);
        if (sbi->s_cluster_ratio == 1 ||
            !ext4_find_delalloc_cluster(inode, lblk, 1))
            ext4_da_release_space(inode, 1);

        num_clusters--;
    }
}

/*
 * Delayed allocation stuff
 */

/*
 * mpage_da_submit_io - walks through extent of pages and try to write
 * them with writepage() call back
 *
 * @mpd->inode: inode
 * @mpd->first_page: first page of the extent
 * @mpd->next_page: page after the last page of the extent
 *
 * By the time mpage_da_submit_io() is called we expect all blocks
 * to be allocated. this may be wrong if allocation failed.
 *
 * As pages are already locked by write_cache_pages(), we can't use it
 */
static int mpage_da_submit_io(struct mpage_da_data *mpd,
                  struct ext4_map_blocks *map)
{
    struct pagevec pvec;
    unsigned long index, end;
    int ret = 0, err, nr_pages, i;
    struct inode *inode = mpd->inode;
    struct address_space *mapping = inode->i_mapping;
    loff_t size = i_size_read(inode);
    unsigned int len, block_start;
    struct buffer_head *bh, *page_bufs = NULL;
    int journal_data = ext4_should_journal_data(inode);
    sector_t pblock = 0, cur_logical = 0;
    struct ext4_io_submit io_submit;

    BUG_ON(mpd->next_page <= mpd->first_page);
    memset(&io_submit, 0, sizeof(io_submit));
    /*
     * We need to start from the first_page to the next_page - 1
     * to make sure we also write the mapped dirty buffer_heads.
     * If we look at mpd->b_blocknr we would only be looking
     * at the currently mapped buffer_heads.
     */
    index = mpd->first_page;
    end = mpd->next_page - 1;

    pagevec_init(&pvec, 0);
    while (index <= end) {
        nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
        if (nr_pages == 0)
            break;
        for (i = 0; i < nr_pages; i++) {
            int commit_write = 0, skip_page = 0;
            struct page *page = pvec.pages[i];

            index = page->index;
            if (index > end)
                break;

            if (index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
            else
                len = PAGE_CACHE_SIZE;
            if (map) {
                cur_logical = index << (PAGE_CACHE_SHIFT -
                            inode->i_blkbits);
                pblock = map->m_pblk + (cur_logical -
                            map->m_lblk);
            }
            index++;

            BUG_ON(!PageLocked(page));
            BUG_ON(PageWriteback(page));

            /*
             * If the page does not have buffers (for
             * whatever reason), try to create them using
             * __block_write_begin.  If this fails,
             * skip the page and move on.
             */
            if (!page_has_buffers(page)) {
                if (__block_write_begin(page, 0, len,
                        noalloc_get_block_write)) {
                skip_page:
                    unlock_page(page);
                    continue;
                }
                commit_write = 1;
            }

            bh = page_bufs = page_buffers(page);
            block_start = 0;
            do {
                if (!bh)
                    goto skip_page;
                if (map && (cur_logical >= map->m_lblk) &&
                    (cur_logical <= (map->m_lblk +
                             (map->m_len - 1)))) {
                    if (buffer_delay(bh)) {
                        clear_buffer_delay(bh);
                        bh->b_blocknr = pblock;
                    }
                    if (buffer_da_mapped(bh))
                        clear_buffer_da_mapped(bh);
                    if (buffer_unwritten(bh) ||
                        buffer_mapped(bh))
                        BUG_ON(bh->b_blocknr != pblock);
                    if (map->m_flags & EXT4_MAP_UNINIT)
                        set_buffer_uninit(bh);
                    clear_buffer_unwritten(bh);
                }

                /*
                 * skip page if block allocation undone and
                 * block is dirty
                 */
                if (ext4_bh_delay_or_unwritten(NULL, bh))
                    skip_page = 1;
                bh = bh->b_this_page;
                block_start += bh->b_size;
                cur_logical++;
                pblock++;
            } while (bh != page_bufs);

            if (skip_page)
                goto skip_page;

            if (commit_write)
                /* mark the buffer_heads as dirty & uptodate */
                block_commit_write(page, 0, len);

            clear_page_dirty_for_io(page);
            /*
             * Delalloc doesn't support data journalling,
             * but eventually maybe we'll lift this
             * restriction.
             */
            if (unlikely(journal_data && PageChecked(page)))
                err = __ext4_journalled_writepage(page, len);
            else if (test_opt(inode->i_sb, MBLK_IO_SUBMIT))
                err = ext4_bio_write_page(&io_submit, page,
                              len, mpd->wbc);
            else if (buffer_uninit(page_bufs)) {
                ext4_set_bh_endio(page_bufs, inode);
                err = block_write_full_page_endio(page,
                    noalloc_get_block_write,
                    mpd->wbc, ext4_end_io_buffer_write);
            } else
                err = block_write_full_page(page,
                    noalloc_get_block_write, mpd->wbc);

            if (!err)
                mpd->pages_written++;
            /*
             * In error case, we have to continue because
             * remaining pages are still locked
             */
            if (ret == 0)
                ret = err;
        }
        pagevec_release(&pvec);
    }
    ext4_io_submit(&io_submit);
    return ret;
}

static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd)
{
    int nr_pages, i;
    pgoff_t index, end;
    struct pagevec pvec;
    struct inode *inode = mpd->inode;
    struct address_space *mapping = inode->i_mapping;

    index = mpd->first_page;
    end   = mpd->next_page - 1;
    while (index <= end) {
        nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
        if (nr_pages == 0)
            break;
        for (i = 0; i < nr_pages; i++) {
            struct page *page = pvec.pages[i];
            if (page->index > end)
                break;
            BUG_ON(!PageLocked(page));
            BUG_ON(PageWriteback(page));
            block_invalidatepage(page, 0);
            ClearPageUptodate(page);
            unlock_page(page);
        }
        index = pvec.pages[nr_pages - 1]->index + 1;
        pagevec_release(&pvec);
    }
    return;
}

static void ext4_print_free_blocks(struct inode *inode)
{
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    struct super_block *sb = inode->i_sb;

    ext4_msg(sb, KERN_CRIT, "Total free blocks count %lld",
           EXT4_C2B(EXT4_SB(inode->i_sb),
            ext4_count_free_clusters(inode->i_sb)));
    ext4_msg(sb, KERN_CRIT, "Free/Dirty block details");
    ext4_msg(sb, KERN_CRIT, "free_blocks=%lld",
           (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
        percpu_counter_sum(&sbi->s_freeclusters_counter)));
    ext4_msg(sb, KERN_CRIT, "dirty_blocks=%lld",
           (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
        percpu_counter_sum(&sbi->s_dirtyclusters_counter)));
    ext4_msg(sb, KERN_CRIT, "Block reservation details");
    ext4_msg(sb, KERN_CRIT, "i_reserved_data_blocks=%u",
         EXT4_I(inode)->i_reserved_data_blocks);
    ext4_msg(sb, KERN_CRIT, "i_reserved_meta_blocks=%u",
           EXT4_I(inode)->i_reserved_meta_blocks);
    return;
}

/*
 * mpage_da_map_and_submit - go through given space, map them
 *       if necessary, and then submit them for I/O
 *
 * @mpd - bh describing space
 *
 * The function skips space we know is already mapped to disk blocks.
 *
 */
static void mpage_da_map_and_submit(struct mpage_da_data *mpd)
{
    int err, blks, get_blocks_flags;
    struct ext4_map_blocks map, *mapp = NULL;
    sector_t next = mpd->b_blocknr;
    unsigned max_blocks = mpd->b_size >> mpd->inode->i_blkbits;
    loff_t disksize = EXT4_I(mpd->inode)->i_disksize;
    handle_t *handle = NULL;

    /*
     * If the blocks are mapped already, or we couldn't accumulate
     * any blocks, then proceed immediately to the submission stage.
     */
    if ((mpd->b_size == 0) ||
        ((mpd->b_state  & (1 << BH_Mapped)) &&
         !(mpd->b_state & (1 << BH_Delay)) &&
         !(mpd->b_state & (1 << BH_Unwritten))))
        goto submit_io;

    handle = ext4_journal_current_handle();
    BUG_ON(!handle);

    /*
     * Call ext4_map_blocks() to allocate any delayed allocation
     * blocks, or to convert an uninitialized extent to be
     * initialized (in the case where we have written into
     * one or more preallocated blocks).
     *
     * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE to
     * indicate that we are on the delayed allocation path.  This
     * affects functions in many different parts of the allocation
     * call path.  This flag exists primarily because we don't
     * want to change *many* call functions, so ext4_map_blocks()
     * will set the EXT4_STATE_DELALLOC_RESERVED flag once the
     * inode's allocation semaphore is taken.
     *
     * If the blocks in questions were delalloc blocks, set
     * EXT4_GET_BLOCKS_DELALLOC_RESERVE so the delalloc accounting
     * variables are updated after the blocks have been allocated.
     */
    map.m_lblk = next;
    map.m_len = max_blocks;
    get_blocks_flags = EXT4_GET_BLOCKS_CREATE;
    if (ext4_should_dioread_nolock(mpd->inode))
        get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
    if (mpd->b_state & (1 << BH_Delay))
        get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;

    blks = ext4_map_blocks(handle, mpd->inode, &map, get_blocks_flags);
    if (blks < 0) {
        struct super_block *sb = mpd->inode->i_sb;

        err = blks;
        /*
         * If get block returns EAGAIN or ENOSPC and there
         * appears to be free blocks we will just let
         * mpage_da_submit_io() unlock all of the pages.
         */
        if (err == -EAGAIN)
            goto submit_io;

        if (err == -ENOSPC && ext4_count_free_clusters(sb)) {
            mpd->retval = err;
            goto submit_io;
        }

        /*
         * get block failure will cause us to loop in
         * writepages, because a_ops->writepage won't be able
         * to make progress. The page will be redirtied by
         * writepage and writepages will again try to write
         * the same.
         */
        if (!(EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED)) {
            ext4_msg(sb, KERN_CRIT,
                 "delayed block allocation failed for inode %lu "
                 "at logical offset %llu with max blocks %zd "
                 "with error %d", mpd->inode->i_ino,
                 (unsigned long long) next,
                 mpd->b_size >> mpd->inode->i_blkbits, err);
            ext4_msg(sb, KERN_CRIT,
                "This should not happen!! Data will be lost\n");
            if (err == -ENOSPC)
                ext4_print_free_blocks(mpd->inode);
        }
        /* invalidate all the pages */
        ext4_da_block_invalidatepages(mpd);

        /* Mark this page range as having been completed */
        mpd->io_done = 1;
        return;
    }
    BUG_ON(blks == 0);

    mapp = &map;
    if (map.m_flags & EXT4_MAP_NEW) {
        struct block_device *bdev = mpd->inode->i_sb->s_bdev;
        int i;

        for (i = 0; i < map.m_len; i++)
            unmap_underlying_metadata(bdev, map.m_pblk + i);

        if (ext4_should_order_data(mpd->inode)) {
            err = ext4_jbd2_file_inode(handle, mpd->inode);
            if (err) {
                /* Only if the journal is aborted */
                mpd->retval = err;
                goto submit_io;
            }
        }
    }

    /*
     * Update on-disk size along with block allocation.
     */
    disksize = ((loff_t) next + blks) << mpd->inode->i_blkbits;
    if (disksize > i_size_read(mpd->inode))
        disksize = i_size_read(mpd->inode);
    if (disksize > EXT4_I(mpd->inode)->i_disksize) {
        ext4_update_i_disksize(mpd->inode, disksize);
        err = ext4_mark_inode_dirty(handle, mpd->inode);
        if (err)
            ext4_error(mpd->inode->i_sb,
                   "Failed to mark inode %lu dirty",
                   mpd->inode->i_ino);
    }

submit_io:
    mpage_da_submit_io(mpd, mapp);
    mpd->io_done = 1;
}

#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | \
        (1 << BH_Delay) | (1 << BH_Unwritten))

/*
 * mpage_add_bh_to_extent - try to add one more block to extent of blocks
 *
 * @mpd->lbh - extent of blocks
 * @logical - logical number of the block in the file
 * @bh - bh of the block (used to access block's state)
 *
 * the function is used to collect contig. blocks in same state
 */
static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
                   sector_t logical, size_t b_size,
                   unsigned long b_state)
{
    sector_t next;
    int nrblocks = mpd->b_size >> mpd->inode->i_blkbits;

    /*
     * XXX Don't go larger than mballoc is willing to allocate
     * This is a stopgap solution.  We eventually need to fold
     * mpage_da_submit_io() into this function and then call
     * ext4_map_blocks() multiple times in a loop
     */
    if (nrblocks >= 8*1024*1024/mpd->inode->i_sb->s_blocksize)
        goto flush_it;

    /* check if thereserved journal credits might overflow */
    if (!(ext4_test_inode_flag(mpd->inode, EXT4_INODE_EXTENTS))) {
        if (nrblocks >= EXT4_MAX_TRANS_DATA) {
            /*
             * With non-extent format we are limited by the journal
             * credit available.  Total credit needed to insert
             * nrblocks contiguous blocks is dependent on the
             * nrblocks.  So limit nrblocks.
             */
            goto flush_it;
        } else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
                EXT4_MAX_TRANS_DATA) {
            /*
             * Adding the new buffer_head would make it cross the
             * allowed limit for which we have journal credit
             * reserved. So limit the new bh->b_size
             */
            b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
                        mpd->inode->i_blkbits;
            /* we will do mpage_da_submit_io in the next loop */
        }
    }
    /*
     * First block in the extent
     */
    if (mpd->b_size == 0) {
        mpd->b_blocknr = logical;
        mpd->b_size = b_size;
        mpd->b_state = b_state & BH_FLAGS;
        return;
    }

    next = mpd->b_blocknr + nrblocks;
    /*
     * Can we merge the block to our big extent?
     */
    if (logical == next && (b_state & BH_FLAGS) == mpd->b_state) {
        mpd->b_size += b_size;
        return;
    }

flush_it:
    /*
     * We couldn't merge the block to our extent, so we
     * need to flush current  extent and start new one
     */
    mpage_da_map_and_submit(mpd);
    return;
}

static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
    return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}

/*
 * This function is grabs code from the very beginning of
 * ext4_map_blocks, but assumes that the caller is from delayed write
 * time. This function looks up the requested blocks and sets the
 * buffer delay bit under the protection of i_data_sem.
 */
static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
                  struct ext4_map_blocks *map,
                  struct buffer_head *bh)
{
    int retval;
    sector_t invalid_block = ~((sector_t) 0xffff);

    if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
        invalid_block = ~0;

    map->m_flags = 0;
    ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
          "logical block %lu\n", inode->i_ino, map->m_len,
          (unsigned long) map->m_lblk);
    /*
     * Try to see if we can get the block without requesting a new
     * file system block.
     */
    down_read((&EXT4_I(inode)->i_data_sem));
    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
        retval = ext4_ext_map_blocks(NULL, inode, map, 0);
    else
        retval = ext4_ind_map_blocks(NULL, inode, map, 0);

    if (retval == 0) {
        /*
         * XXX: __block_prepare_write() unmaps passed block,
         * is it OK?
         */
        /* If the block was allocated from previously allocated cluster,
         * then we dont need to reserve it again. */
        if (!(map->m_flags & EXT4_MAP_FROM_CLUSTER)) {
            retval = ext4_da_reserve_space(inode, iblock);
            if (retval)
                /* not enough space to reserve */
                goto out_unlock;
        }

        /* Clear EXT4_MAP_FROM_CLUSTER flag since its purpose is served
         * and it should not appear on the bh->b_state.
         */
        map->m_flags &= ~EXT4_MAP_FROM_CLUSTER;

        map_bh(bh, inode->i_sb, invalid_block);
        set_buffer_new(bh);
        set_buffer_delay(bh);
    }

out_unlock:
    up_read((&EXT4_I(inode)->i_data_sem));

    return retval;
}

/*
 * This is a special get_blocks_t callback which is used by
 * ext4_da_write_begin().  It will either return mapped block or
 * reserve space for a single block.
 *
 * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
 * We also have b_blocknr = -1 and b_bdev initialized properly
 *
 * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
 * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
 * initialized properly.
 */
static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                  struct buffer_head *bh, int create)
{
    struct ext4_map_blocks map;
    int ret = 0;

    BUG_ON(create == 0);
    BUG_ON(bh->b_size != inode->i_sb->s_blocksize);

    map.m_lblk = iblock;
    map.m_len = 1;

    /*
     * first, we need to know whether the block is allocated already
     * preallocated blocks are unmapped but should treated
     * the same as allocated blocks.
     */
    ret = ext4_da_map_blocks(inode, iblock, &map, bh);
    if (ret <= 0)
        return ret;

    map_bh(bh, inode->i_sb, map.m_pblk);
    bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;

    if (buffer_unwritten(bh)) {
        /* A delayed write to unwritten bh should be marked
         * new and mapped.  Mapped ensures that we don't do
         * get_block multiple times when we write to the same
         * offset and new ensures that we do proper zero out
         * for partial write.
         */
        set_buffer_new(bh);
        set_buffer_mapped(bh);
    }
    return 0;
}

/*
 * This function is used as a standard get_block_t calback function
 * when there is no desire to allocate any blocks.  It is used as a
 * callback function for block_write_begin() and block_write_full_page().
 * These functions should only try to map a single block at a time.
 *
 * Since this function doesn't do block allocations even if the caller
 * requests it by passing in create=1, it is critically important that
 * any caller checks to make sure that any buffer heads are returned
 * by this function are either all already mapped or marked for
 * delayed allocation before calling  block_write_full_page().  Otherwise,
 * b_blocknr could be left unitialized, and the page write functions will
 * be taken by surprise.
 */
static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
    BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
    return _ext4_get_block(inode, iblock, bh_result, 0);
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
    get_bh(bh);
    return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
    put_bh(bh);
    return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                       unsigned int len)
{
    struct address_space *mapping = page->mapping;
    struct inode *inode = mapping->host;
    struct buffer_head *page_bufs;
    handle_t *handle = NULL;
    int ret = 0;
    int err;

    ClearPageChecked(page);
    page_bufs = page_buffers(page);
    BUG_ON(!page_bufs);
    walk_page_buffers(handle, page_bufs, 0, len, NULL, bget_one);
    /* As soon as we unlock the page, it can go away, but we have
     * references to buffers so we are safe */
    unlock_page(page);

    handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
    if (IS_ERR(handle)) {
        ret = PTR_ERR(handle);
        goto out;
    }

    BUG_ON(!ext4_handle_valid(handle));

    ret = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                do_journal_get_write_access);

    err = walk_page_buffers(handle, page_bufs, 0, len, NULL,
                write_end_fn);
    if (ret == 0)
        ret = err;
    EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
    err = ext4_journal_stop(handle);
    if (!ret)
        ret = err;

    walk_page_buffers(handle, page_bufs, 0, len, NULL, bput_one);
    ext4_set_inode_state(inode, EXT4_STATE_JDATA);
out:
    return ret;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), no one guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * This function can get called via...
 *   - ext4_da_writepages after taking page lock (have journal handle)
 *   - journal_submit_inode_data_buffers (no journal handle)
 *   - shrink_page_list via the kswapd/direct reclaim (no journal handle)
 *   - grab_page_cache when doing write_begin (have journal handle)
 *
 * We don't do any block allocation in this function. If we have page with
 * multiple blocks we need to write those buffer_heads that are mapped. This
 * is important for mmaped based write. So if we do with blocksize 1K
 * truncate(f, 1024);
 * a = mmap(f, 0, 4096);
 * a[0] = 'a';
 * truncate(f, 4096);
 * we have in the page first buffer_head mapped via page_mkwrite call back
 * but other buffer_heads would be unmapped but dirty (dirty done via the
 * do_wp_page). So writepage should write the first block. If we modify
 * the mmap area beyond 1024 we will again get a page_fault and the
 * page_mkwrite callback will do the block allocation and mark the
 * buffer_heads mapped.
 *
 * We redirty the page if we have any buffer_heads that is either delay or
 * unwritten in the page.
 *
 * We can get recursively called as show below.
 *
 *  ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *      ext4_writepage()
 *
 * But since we don't do any block allocation we should not deadlock.
 * Page also have the dirty flag cleared so we don't get recurive page_lock.
 */
static int ext4_writepage(struct page *page,
              struct writeback_control *wbc)
{
    int ret = 0, commit_write = 0;
    loff_t size;
    unsigned int len;
    struct buffer_head *page_bufs = NULL;
    struct inode *inode = page->mapping->host;

    trace_ext4_writepage(page);
    size = i_size_read(inode);
    if (page->index == size >> PAGE_CACHE_SHIFT)
        len = size & ~PAGE_CACHE_MASK;
    else
        len = PAGE_CACHE_SIZE;

    /*
     * If the page does not have buffers (for whatever reason),
     * try to create them using __block_write_begin.  If this
     * fails, redirty the page and move on.
     */
    if (!page_has_buffers(page)) {
        if (__block_write_begin(page, 0, len,
                    noalloc_get_block_write)) {
        redirty_page:
            redirty_page_for_writepage(wbc, page);
            unlock_page(page);
            return 0;
        }
        commit_write = 1;
    }
    page_bufs = page_buffers(page);
    if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                  ext4_bh_delay_or_unwritten)) {
        /*
         * We don't want to do block allocation, so redirty
         * the page and return.  We may reach here when we do
         * a journal commit via journal_submit_inode_data_buffers.
         * We can also reach here via shrink_page_list but it
         * should never be for direct reclaim so warn if that
         * happens
         */
        WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
                                PF_MEMALLOC);
        goto redirty_page;
    }
    if (commit_write)
        /* now mark the buffer_heads as dirty and uptodate */
        block_commit_write(page, 0, len);

    if (PageChecked(page) && ext4_should_journal_data(inode))
        /*
         * It's mmapped pagecache.  Add buffers and journal it.  There
         * doesn't seem much point in redirtying the page here.
         */
        return __ext4_journalled_writepage(page, len);

    if (buffer_uninit(page_bufs)) {
        ext4_set_bh_endio(page_bufs, inode);
        ret = block_write_full_page_endio(page, noalloc_get_block_write,
                        wbc, ext4_end_io_buffer_write);
    } else
        ret = block_write_full_page(page, noalloc_get_block_write,
                        wbc);

    return ret;
}

/*
 * This is called via ext4_da_writepages() to
 * calculate the total number of credits to reserve to fit
 * a single extent allocation into a single transaction,
 * ext4_da_writpeages() will loop calling this before
 * the block allocation.
 */

static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
    int max_blocks = EXT4_I(inode)->i_reserved_data_blocks;

    /*
     * With non-extent format the journal credit needed to
     * insert nrblocks contiguous block is dependent on
     * number of contiguous block. So we will limit
     * number of contiguous block to a sane value
     */
    if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) &&
        (max_blocks > EXT4_MAX_TRANS_DATA))
        max_blocks = EXT4_MAX_TRANS_DATA;

    return ext4_chunk_trans_blocks(inode, max_blocks);
}

/*
 * write_cache_pages_da - walk the list of dirty pages of the given
 * address space and accumulate pages that need writing, and call
 * mpage_da_map_and_submit to map a single contiguous memory region
 * and then write them.
 */
static int write_cache_pages_da(struct address_space *mapping,
                struct writeback_control *wbc,
                struct mpage_da_data *mpd,
                pgoff_t *done_index)
{
    struct buffer_head  *bh, *head;
    struct inode        *inode = mapping->host;
    struct pagevec      pvec;
    unsigned int        nr_pages;
    sector_t        logical;
    pgoff_t         index, end;
    long            nr_to_write = wbc->nr_to_write;
    int         i, tag, ret = 0;

    memset(mpd, 0, sizeof(struct mpage_da_data));
    mpd->wbc = wbc;
    mpd->inode = inode;
    pagevec_init(&pvec, 0);
    index = wbc->range_start >> PAGE_CACHE_SHIFT;
    end = wbc->range_end >> PAGE_CACHE_SHIFT;

    if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
        tag = PAGECACHE_TAG_TOWRITE;
    else
        tag = PAGECACHE_TAG_DIRTY;

    *done_index = index;
    while (index <= end) {
        nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                  min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
        if (nr_pages == 0)
            return 0;

        for (i = 0; i < nr_pages; i++) {
            struct page *page = pvec.pages[i];

            /*
             * At this point, the page may be truncated or
             * invalidated (changing page->mapping to NULL), or
             * even swizzled back from swapper_space to tmpfs file
             * mapping. However, page->index will not change
             * because we have a reference on the page.
             */
            if (page->index > end)
                goto out;

            *done_index = page->index + 1;

            /*
             * If we can't merge this page, and we have
             * accumulated an contiguous region, write it
             */
            if ((mpd->next_page != page->index) &&
                (mpd->next_page != mpd->first_page)) {
                mpage_da_map_and_submit(mpd);
                goto ret_extent_tail;
            }

            lock_page(page);

            /*
             * If the page is no longer dirty, or its
             * mapping no longer corresponds to inode we
             * are writing (which means it has been
             * truncated or invalidated), or the page is
             * already under writeback and we are not
             * doing a data integrity writeback, skip the page
             */
            if (!PageDirty(page) ||
                (PageWriteback(page) &&
                 (wbc->sync_mode == WB_SYNC_NONE)) ||
                unlikely(page->mapping != mapping)) {
                unlock_page(page);
                continue;
            }

            wait_on_page_writeback(page);
            BUG_ON(PageWriteback(page));

            if (mpd->next_page != page->index)
                mpd->first_page = page->index;
            mpd->next_page = page->index + 1;
            logical = (sector_t) page->index <<
                (PAGE_CACHE_SHIFT - inode->i_blkbits);

            if (!page_has_buffers(page)) {
                mpage_add_bh_to_extent(mpd, logical,
                               PAGE_CACHE_SIZE,
                               (1 << BH_Dirty) | (1 << BH_Uptodate));
                if (mpd->io_done)
                    goto ret_extent_tail;
            } else {
                /*
                 * Page with regular buffer heads,
                 * just add all dirty ones
                 */
                head = page_buffers(page);
                bh = head;
                do {
                    BUG_ON(buffer_locked(bh));
                    /*
                     * We need to try to allocate
                     * unmapped blocks in the same page.
                     * Otherwise we won't make progress
                     * with the page in ext4_writepage
                     */
                    if (ext4_bh_delay_or_unwritten(NULL, bh)) {
                        mpage_add_bh_to_extent(mpd, logical,
                                       bh->b_size,
                                       bh->b_state);
                        if (mpd->io_done)
                            goto ret_extent_tail;
                    } else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
                        /*
                         * mapped dirty buffer. We need
                         * to update the b_state
                         * because we look at b_state
                         * in mpage_da_map_blocks.  We
                         * don't update b_size because
                         * if we find an unmapped
                         * buffer_head later we need to
                         * use the b_state flag of that
                         * buffer_head.
                         */
                        if (mpd->b_size == 0)
                            mpd->b_state = bh->b_state & BH_FLAGS;
                    }
                    logical++;
                } while ((bh = bh->b_this_page) != head);
            }

            if (nr_to_write > 0) {
                nr_to_write--;
                if (nr_to_write == 0 &&
                    wbc->sync_mode == WB_SYNC_NONE)
                    /*
                     * We stop writing back only if we are
                     * not doing integrity sync. In case of
                     * integrity sync we have to keep going
                     * because someone may be concurrently
                     * dirtying pages, and we might have
                     * synced a lot of newly appeared dirty
                     * pages, but have not synced all of the
                     * old dirty pages.
                     */
                    goto out;
            }
        }
        pagevec_release(&pvec);
        cond_resched();
    }
    return 0;
ret_extent_tail:
    ret = MPAGE_DA_EXTENT_TAIL;
out:
    pagevec_release(&pvec);
    cond_resched();
    return ret;
}


static int ext4_da_writepages(struct address_space *mapping,
                  struct writeback_control *wbc)
{
    pgoff_t index;
    int range_whole = 0;
    handle_t *handle = NULL;
    struct mpage_da_data mpd;
    struct inode *inode = mapping->host;
    int pages_written = 0;
    unsigned int max_pages;
    int range_cyclic, cycled = 1, io_done = 0;
    int needed_blocks, ret = 0;
    long desired_nr_to_write, nr_to_writebump = 0;
    loff_t range_start = wbc->range_start;
    struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
    pgoff_t done_index = 0;
    pgoff_t end;
    struct blk_plug plug;

    trace_ext4_da_writepages(inode, wbc);

    /*
     * No pages to write? This is mainly a kludge to avoid starting
     * a transaction for special inodes like journal inode on last iput()
     * because that could violate lock ordering on umount
     */
    if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
        return 0;

    /*
     * If the filesystem has aborted, it is read-only, so return
     * right away instead of dumping stack traces later on that
     * will obscure the real source of the problem.  We test
     * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
     * the latter could be true if the filesystem is mounted
     * read-only, and in that case, ext4_da_writepages should
     * *never* be called, so if that ever happens, we would want
     * the stack trace.
     */
    if (unlikely(sbi->s_mount_flags & EXT4_MF_FS_ABORTED))
        return -EROFS;

    if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
        range_whole = 1;

    range_cyclic = wbc->range_cyclic;
    if (wbc->range_cyclic) {
        index = mapping->writeback_index;
        if (index)
            cycled = 0;
        wbc->range_start = index << PAGE_CACHE_SHIFT;
        wbc->range_end  = LLONG_MAX;
        wbc->range_cyclic = 0;
        end = -1;
    } else {
        index = wbc->range_start >> PAGE_CACHE_SHIFT;
        end = wbc->range_end >> PAGE_CACHE_SHIFT;
    }

    /*
     * This works around two forms of stupidity.  The first is in
     * the writeback code, which caps the maximum number of pages
     * written to be 1024 pages.  This is wrong on multiple
     * levels; different architectues have a different page size,
     * which changes the maximum amount of data which gets
     * written.  Secondly, 4 megabytes is way too small.  XFS
     * forces this value to be 16 megabytes by multiplying
     * nr_to_write parameter by four, and then relies on its
     * allocator to allocate larger extents to make them
     * contiguous.  Unfortunately this brings us to the second
     * stupidity, which is that ext4's mballoc code only allocates
     * at most 2048 blocks.  So we force contiguous writes up to
     * the number of dirty blocks in the inode, or
     * sbi->max_writeback_mb_bump whichever is smaller.
     */
    max_pages = sbi->s_max_writeback_mb_bump << (20 - PAGE_CACHE_SHIFT);
    if (!range_cyclic && range_whole) {
        if (wbc->nr_to_write == LONG_MAX)
            desired_nr_to_write = wbc->nr_to_write;
        else
            desired_nr_to_write = wbc->nr_to_write * 8;
    } else
        desired_nr_to_write = ext4_num_dirty_pages(inode, index,
                               max_pages);
    if (desired_nr_to_write > max_pages)
        desired_nr_to_write = max_pages;

    if (wbc->nr_to_write < desired_nr_to_write) {
        nr_to_writebump = desired_nr_to_write - wbc->nr_to_write;
        wbc->nr_to_write = desired_nr_to_write;
    }

retry:
    if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
        tag_pages_for_writeback(mapping, index, end);

    blk_start_plug(&plug);
    while (!ret && wbc->nr_to_write > 0) {

        /*
         * we  insert one extent at a time. So we need
         * credit needed for single extent allocation.
         * journalled mode is currently not supported
         * by delalloc
         */
        BUG_ON(ext4_should_journal_data(inode));
        needed_blocks = ext4_da_writepages_trans_blocks(inode);

        /* start a new transaction*/
        handle = ext4_journal_start(inode, needed_blocks);
        if (IS_ERR(handle)) {
            ret = PTR_ERR(handle);
            ext4_msg(inode->i_sb, KERN_CRIT, "%s: jbd2_start: "
                   "%ld pages, ino %lu; err %d", __func__,
                wbc->nr_to_write, inode->i_ino, ret);
            blk_finish_plug(&plug);
            goto out_writepages;
        }

        /*
         * Now call write_cache_pages_da() to find the next
         * contiguous region of logical blocks that need
         * blocks to be allocated by ext4 and submit them.
         */
        ret = write_cache_pages_da(mapping, wbc, &mpd, &done_index);
        /*
         * If we have a contiguous extent of pages and we
         * haven't done the I/O yet, map the blocks and submit
         * them for I/O.
         */
        if (!mpd.io_done && mpd.next_page != mpd.first_page) {
            mpage_da_map_and_submit(&mpd);
            ret = MPAGE_DA_EXTENT_TAIL;
        }
        trace_ext4_da_write_pages(inode, &mpd);
        wbc->nr_to_write -= mpd.pages_written;

        ext4_journal_stop(handle);

        if ((mpd.retval == -ENOSPC) && sbi->s_journal) {
            /* commit the transaction which would
             * free blocks released in the transaction
             * and try again
             */
            jbd2_journal_force_commit_nested(sbi->s_journal);
            ret = 0;
        } else if (ret == MPAGE_DA_EXTENT_TAIL) {
            /*
             * Got one extent now try with rest of the pages.
             * If mpd.retval is set -EIO, journal is aborted.
             * So we don't need to write any more.
             */
            pages_written += mpd.pages_written;
            ret = mpd.retval;
            io_done = 1;
        } else if (wbc->nr_to_write)
            /*
             * There is no more writeout needed
             * or we requested for a noblocking writeout
             * and we found the device congested
             */
            break;
    }
    blk_finish_plug(&plug);
    if (!io_done && !cycled) {
        cycled = 1;
        index = 0;
        wbc->range_start = index << PAGE_CACHE_SHIFT;
        wbc->range_end  = mapping->writeback_index - 1;
        goto retry;
    }

    /* Update index */
    wbc->range_cyclic = range_cyclic;
    if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
        /*
         * set the writeback_index so that range_cyclic
         * mode will write it back later
         */
        mapping->writeback_index = done_index;

out_writepages:
    wbc->nr_to_write -= nr_to_writebump;
    wbc->range_start = range_start;
    trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);
    return ret;
}

#define FALL_BACK_TO_NONDELALLOC 1
static int ext4_nonda_switch(struct super_block *sb)
{
    s64 free_blocks, dirty_blocks;
    struct ext4_sb_info *sbi = EXT4_SB(sb);

    /*
     * switch to non delalloc mode if we are running low
     * on free block. The free block accounting via percpu
     * counters can get slightly wrong with percpu_counter_batch getting
     * accumulated on each CPU without updating global counters
     * Delalloc need an accurate free block accounting. So switch
     * to non delalloc when we are near to error range.
     */
    free_blocks  = EXT4_C2B(sbi,
        percpu_counter_read_positive(&sbi->s_freeclusters_counter));
    dirty_blocks = percpu_counter_read_positive(&sbi->s_dirtyclusters_counter);
    /*
     * Start pushing delalloc when 1/2 of free blocks are dirty.
     */
    if (dirty_blocks && (free_blocks < 2 * dirty_blocks) &&
        !writeback_in_progress(sb->s_bdi) &&
        down_read_trylock(&sb->s_umount)) {
        writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);
        up_read(&sb->s_umount);
    }

    if (2 * free_blocks < 3 * dirty_blocks ||
        free_blocks < (dirty_blocks + EXT4_FREECLUSTERS_WATERMARK)) {
        /*
         * free block count is less than 150% of dirty blocks
         * or free blocks is less than watermark
         */
        return 1;
    }
    return 0;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
                   loff_t pos, unsigned len, unsigned flags,
                   struct page **pagep, void **fsdata)
{
    int ret, retries = 0;
    struct page *page;
    pgoff_t index;
    struct inode *inode = mapping->host;
    handle_t *handle;

    index = pos >> PAGE_CACHE_SHIFT;

    if (ext4_nonda_switch(inode->i_sb)) {
        *fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
        return ext4_write_begin(file, mapping, pos,
                    len, flags, pagep, fsdata);
    }
    *fsdata = (void *)0;
    trace_ext4_da_write_begin(inode, pos, len, flags);
retry:
    /*
     * With delayed allocation, we don't log the i_disksize update
     * if there is delayed block allocation. But we still need
     * to journalling the i_disksize update if writes to the end
     * of file which has an already mapped buffer.
     */
    handle = ext4_journal_start(inode, 1);
    if (IS_ERR(handle)) {
        ret = PTR_ERR(handle);
        goto out;
    }
    /* We cannot recurse into the filesystem as the transaction is already
     * started */
    flags |= AOP_FLAG_NOFS;

    page = grab_cache_page_write_begin(mapping, index, flags);
    if (!page) {
        ext4_journal_stop(handle);
        ret = -ENOMEM;
        goto out;
    }
    *pagep = page;

    ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
    if (ret < 0) {
        unlock_page(page);
        ext4_journal_stop(handle);
        page_cache_release(page);
        /*
         * block_write_begin may have instantiated a few blocks
         * outside i_size.  Trim these off again. Don't need
         * i_size_read because we hold i_mutex.
         */
        if (pos + len > inode->i_size)
            ext4_truncate_failed_write(inode);
    }

    if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
        goto retry;
out:
    return ret;
}

/*
 * Check if we should update i_disksize
 * when write to the end of file but not require block allocation
 */
static int ext4_da_should_update_i_disksize(struct page *page,
                        unsigned long offset)
{
    struct buffer_head *bh;
    struct inode *inode = page->mapping->host;
    unsigned int idx;
    int i;

    bh = page_buffers(page);
    idx = offset >> inode->i_blkbits;

    for (i = 0; i < idx; i++)
        bh = bh->b_this_page;

    if (!buffer_mapped(bh) || (buffer_delay(bh)) || buffer_unwritten(bh))
        return 0;
    return 1;
}

static int ext4_da_write_end(struct file *file,
                 struct address_space *mapping,
                 loff_t pos, unsigned len, unsigned copied,
                 struct page *page, void *fsdata)
{
    struct inode *inode = mapping->host;
    int ret = 0, ret2;
    handle_t *handle = ext4_journal_current_handle();
    loff_t new_i_size;
    unsigned long start, end;
    int write_mode = (int)(unsigned long)fsdata;

    if (write_mode == FALL_BACK_TO_NONDELALLOC) {
        switch (ext4_inode_journal_mode(inode)) {
        case EXT4_INODE_ORDERED_DATA_MODE:
            return ext4_ordered_write_end(file, mapping, pos,
                    len, copied, page, fsdata);
        case EXT4_INODE_WRITEBACK_DATA_MODE:
            return ext4_writeback_write_end(file, mapping, pos,
                    len, copied, page, fsdata);
        default:
            BUG();
        }
    }

    trace_ext4_da_write_end(inode, pos, len, copied);
    start = pos & (PAGE_CACHE_SIZE - 1);
    end = start + copied - 1;

    /*
     * generic_write_end() will run mark_inode_dirty() if i_size
     * changes.  So let's piggyback the i_disksize mark_inode_dirty
     * into that.
     */

    new_i_size = pos + copied;
    if (copied && new_i_size > EXT4_I(inode)->i_disksize) {
        if (ext4_da_should_update_i_disksize(page, end)) {
            down_write(&EXT4_I(inode)->i_data_sem);
            if (new_i_size > EXT4_I(inode)->i_disksize) {
                /*
                 * Updating i_disksize when extending file
                 * without needing block allocation
                 */
                if (ext4_should_order_data(inode))
                    ret = ext4_jbd2_file_inode(handle,
                                   inode);

                EXT4_I(inode)->i_disksize = new_i_size;
            }
            up_write(&EXT4_I(inode)->i_data_sem);
            /* We need to mark inode dirty even if
             * new_i_size is less that inode->i_size
             * bu greater than i_disksize.(hint delalloc)
             */
            ext4_mark_inode_dirty(handle, inode);
        }
    }
    ret2 = generic_write_end(file, mapping, pos, len, copied,
                            page, fsdata);
    copied = ret2;
    if (ret2 < 0)
        ret = ret2;
    ret2 = ext4_journal_stop(handle);
    if (!ret)
        ret = ret2;

    return ret ? ret : copied;
}

static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
{
    /*
     * Drop reserved blocks
     */
    BUG_ON(!PageLocked(page));
    if (!page_has_buffers(page))
        goto out;

    ext4_da_page_release_reservation(page, offset);

out:
    ext4_invalidatepage(page, offset);

    return;
}

/*
 * Force all delayed allocation blocks to be allocated for a given inode.
 */
int ext4_alloc_da_blocks(struct inode *inode)
{
    trace_ext4_alloc_da_blocks(inode);

    if (!EXT4_I(inode)->i_reserved_data_blocks &&
        !EXT4_I(inode)->i_reserved_meta_blocks)
        return 0;

    /*
     * We do something simple for now.  The filemap_flush() will
     * also start triggering a write of the data blocks, which is
     * not strictly speaking necessary (and for users of
     * laptop_mode, not even desirable).  However, to do otherwise
     * would require replicating code paths in:
     *
     * ext4_da_writepages() ->
     *    write_cache_pages() ---> (via passed in callback function)
     *        __mpage_da_writepage() -->
     *           mpage_add_bh_to_extent()
     *           mpage_da_map_blocks()
     *
     * The problem is that write_cache_pages(), located in
     * mm/page-writeback.c, marks pages clean in preparation for
     * doing I/O, which is not desirable if we're not planning on
     * doing I/O at all.
     *
     * We could call write_cache_pages(), and then redirty all of
     * the pages by calling redirty_page_for_writepage() but that
     * would be ugly in the extreme.  So instead we would need to
     * replicate parts of the code in the above functions,
     * simplifying them because we wouldn't actually intend to
     * write out the pages, but rather only collect contiguous
     * logical block extents, call the multi-block allocator, and
     * then update the buffer heads with the block allocations.
     *
     * For now, though, we'll cheat by calling filemap_flush(),
     * which will map the blocks, and start the I/O, but not
     * actually wait for the I/O to complete.
     */
    return filemap_flush(inode->i_mapping);
}

/*
 * bmap() is special.  It gets used by applications such as lilo and by
 * the swapper to find the on-disk block of a specific piece of data.
 *
 * Naturally, this is dangerous if the block concerned is still in the
 * journal.  If somebody makes a swapfile on an ext4 data-journaling
 * filesystem and enables swap, then they may get a nasty shock when the
 * data getting swapped to that swapfile suddenly gets overwritten by
 * the original zero's written out previously to the journal and
 * awaiting writeback in the kernel's buffer cache.
 *
 * So, if we see any bmap calls here on a modified, data-journaled file,
 * take extra steps to flush any blocks which might be in the cache.
 */
static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
{
    struct inode *inode = mapping->host;
    journal_t *journal;
    int err;

    if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
            test_opt(inode->i_sb, DELALLOC)) {
        /*
         * With delalloc we want to sync the file
         * so that we can make sure we allocate
         * blocks for file
         */
        filemap_write_and_wait(mapping);
    }

    if (EXT4_JOURNAL(inode) &&
        ext4_test_inode_state(inode, EXT4_STATE_JDATA)) {
        /*
         * This is a REALLY heavyweight approach, but the use of
         * bmap on dirty files is expected to be extremely rare:
         * only if we run lilo or swapon on a freshly made file
         * do we expect this to happen.
         *
         * (bmap requires CAP_SYS_RAWIO so this does not
         * represent an unprivileged user DOS attack --- we'd be
         * in trouble if mortal users could trigger this path at
         * will.)
         *
         * NB. EXT4_STATE_JDATA is not set on files other than
         * regular files.  If somebody wants to bmap a directory
         * or symlink and gets confused because the buffer
         * hasn't yet been flushed to disk, they deserve
         * everything they get.
         */

        ext4_clear_inode_state(inode, EXT4_STATE_JDATA);
        journal = EXT4_JOURNAL(inode);
        jbd2_journal_lock_updates(journal);
        err = jbd2_journal_flush(journal);
        jbd2_journal_unlock_updates(journal);

        if (err)
            return 0;
    }

    return generic_block_bmap(mapping, block, ext4_get_block);
}

static int ext4_readpage(struct file *file, struct page *page)
{
    trace_ext4_readpage(page);
    return mpage_readpage(page, ext4_get_block);
}

static int
ext4_readpages(struct file *file, struct address_space *mapping,
        struct list_head *pages, unsigned nr_pages)
{
    return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
}

static void ext4_invalidatepage_free_endio(struct page *page, unsigned long offset)
{
    struct buffer_head *head, *bh;
    unsigned int curr_off = 0;

    if (!page_has_buffers(page))
        return;
    head = bh = page_buffers(page);
    do {
        if (offset <= curr_off && test_clear_buffer_uninit(bh)
                    && bh->b_private) {
            ext4_free_io_end(bh->b_private);
            bh->b_private = NULL;
            bh->b_end_io = NULL;
        }
        curr_off = curr_off + bh->b_size;
        bh = bh->b_this_page;
    } while (bh != head);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset)
{
    journal_t *journal = EXT4_JOURNAL(page->mapping->host);

    trace_ext4_invalidatepage(page, offset);

    /*
     * free any io_end structure allocated for buffers to be discarded
     */
    if (ext4_should_dioread_nolock(page->mapping->host))
        ext4_invalidatepage_free_endio(page, offset);
    /*
     * If it's a full truncate we just forget about the pending dirtying
     */
    if (offset == 0)
        ClearPageChecked(page);

    if (journal)
        jbd2_journal_invalidatepage(journal, page, offset);
    else
        block_invalidatepage(page, offset);
}

static int ext4_releasepage(struct page *page, gfp_t wait)
{
    journal_t *journal = EXT4_JOURNAL(page->mapping->host);

    trace_ext4_releasepage(page);

    WARN_ON(PageChecked(page));
    if (!page_has_buffers(page))
        return 0;
    if (journal)
        return jbd2_journal_try_to_free_buffers(journal, page, wait);
    else
        return try_to_free_buffers(page);
}

/*
 * ext4_get_block used when preparing for a DIO write or buffer write.
 * We allocate an uinitialized extent if blocks haven't been allocated.
 * The extent will be converted to initialized after the IO is complete.
 */
static int ext4_get_block_write(struct inode *inode, sector_t iblock,
           struct buffer_head *bh_result, int create)
{
    ext4_debug("ext4_get_block_write: inode %lu, create flag %d\n",
           inode->i_ino, create);
    return _ext4_get_block(inode, iblock, bh_result,
                   EXT4_GET_BLOCKS_IO_CREATE_EXT);
}

static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
           struct buffer_head *bh_result, int flags)
{
    handle_t *handle = ext4_journal_current_handle();
    struct ext4_map_blocks map;
    int ret = 0;

    ext4_debug("ext4_get_block_write_nolock: inode %lu, flag %d\n",
           inode->i_ino, flags);

    flags = EXT4_GET_BLOCKS_NO_LOCK;

    map.m_lblk = iblock;
    map.m_len = bh_result->b_size >> inode->i_blkbits;

    ret = ext4_map_blocks(handle, inode, &map, flags);
    if (ret > 0) {
        map_bh(bh_result, inode->i_sb, map.m_pblk);
        bh_result->b_state = (bh_result->b_state & ~EXT4_MAP_FLAGS) |
                    map.m_flags;
        bh_result->b_size = inode->i_sb->s_blocksize * map.m_len;
        ret = 0;
    }
    return ret;
}

static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
                ssize_t size, void *private, int ret,
                bool is_async)
{
    struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
        ext4_io_end_t *io_end = iocb->private;

    /* if not async direct IO or dio with 0 bytes write, just return */
    if (!io_end || !size)
        goto out;

    ext_debug("ext4_end_io_dio(): io_end 0x%p "
          "for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
          iocb->private, io_end->inode->i_ino, iocb, offset,
          size);

    iocb->private = NULL;

    /* if not aio dio with unwritten extents, just free io and return */
    if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
        ext4_free_io_end(io_end);
out:
        if (is_async)
            aio_complete(iocb, ret, 0);
        inode_dio_done(inode);
        return;
    }

    io_end->offset = offset;
    io_end->size = size;
    if (is_async) {
        io_end->iocb = iocb;
        io_end->result = ret;
    }

    ext4_add_complete_io(io_end);
}

static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
{
    ext4_io_end_t *io_end = bh->b_private;
    struct inode *inode;

    if (!test_clear_buffer_uninit(bh) || !io_end)
        goto out;

    if (!(io_end->inode->i_sb->s_flags & MS_ACTIVE)) {
        ext4_msg(io_end->inode->i_sb, KERN_INFO,
             "sb umounted, discard end_io request for inode %lu",
             io_end->inode->i_ino);
        ext4_free_io_end(io_end);
        goto out;
    }

    /*
     * It may be over-defensive here to check EXT4_IO_END_UNWRITTEN now,
     * but being more careful is always safe for the future change.
     */
    inode = io_end->inode;
    ext4_set_io_unwritten_flag(inode, io_end);
    ext4_add_complete_io(io_end);
out:
    bh->b_private = NULL;
    bh->b_end_io = NULL;
    clear_buffer_uninit(bh);
    end_buffer_async_write(bh, uptodate);
}

static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode)
{
    ext4_io_end_t *io_end;
    struct page *page = bh->b_page;
    loff_t offset = (sector_t)page->index << PAGE_CACHE_SHIFT;
    size_t size = bh->b_size;

retry:
    io_end = ext4_init_io_end(inode, GFP_ATOMIC);
    if (!io_end) {
        pr_warn_ratelimited("%s: allocation fail\n", __func__);
        schedule();
        goto retry;
    }
    io_end->offset = offset;
    io_end->size = size;
    /*
     * We need to hold a reference to the page to make sure it
     * doesn't get evicted before ext4_end_io_work() has a chance
     * to convert the extent from written to unwritten.
     */
    io_end->page = page;
    get_page(io_end->page);

    bh->b_private = io_end;
    bh->b_end_io = ext4_end_io_buffer_write;
    return 0;
}

/*
 * For ext4 extent files, ext4 will do direct-io write to holes,
 * preallocated extents, and those write extend the file, no need to
 * fall back to buffered IO.
 *
 * For holes, we fallocate those blocks, mark them as uninitialized
 * If those blocks were preallocated, we mark sure they are splited, but
 * still keep the range to write as uninitialized.
 *
 * The unwrritten extents will be converted to written when DIO is completed.
 * For async direct IO, since the IO may still pending when return, we
 * set up an end_io call back function, which will do the conversion
 * when async direct IO completed.
 *
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 */
static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
                  const struct iovec *iov, loff_t offset,
                  unsigned long nr_segs)
{
    struct file *file = iocb->ki_filp;
    struct inode *inode = file->f_mapping->host;
    ssize_t ret;
    size_t count = iov_length(iov, nr_segs);

    loff_t final_size = offset + count;
    if (rw == WRITE && final_size <= inode->i_size) {
        int overwrite = 0;

        BUG_ON(iocb->private == NULL);

        /* If we do a overwrite dio, i_mutex locking can be released */
        overwrite = *((int *)iocb->private);

        if (overwrite) {
            atomic_inc(&inode->i_dio_count);
            down_read(&EXT4_I(inode)->i_data_sem);
            mutex_unlock(&inode->i_mutex);
        }

        /*
         * We could direct write to holes and fallocate.
         *
         * Allocated blocks to fill the hole are marked as uninitialized
         * to prevent parallel buffered read to expose the stale data
         * before DIO complete the data IO.
         *
         * As to previously fallocated extents, ext4 get_block
         * will just simply mark the buffer mapped but still
         * keep the extents uninitialized.
         *
         * for non AIO case, we will convert those unwritten extents
         * to written after return back from blockdev_direct_IO.
         *
         * for async DIO, the conversion needs to be defered when
         * the IO is completed. The ext4 end_io callback function
         * will be called to take care of the conversion work.
         * Here for async case, we allocate an io_end structure to
         * hook to the iocb.
         */
        iocb->private = NULL;
        ext4_inode_aio_set(inode, NULL);
        if (!is_sync_kiocb(iocb)) {
            ext4_io_end_t *io_end =
                ext4_init_io_end(inode, GFP_NOFS);
            if (!io_end) {
                ret = -ENOMEM;
                goto retake_lock;
            }
            io_end->flag |= EXT4_IO_END_DIRECT;
            iocb->private = io_end;
            /*
             * we save the io structure for current async
             * direct IO, so that later ext4_map_blocks()
             * could flag the io structure whether there
             * is a unwritten extents needs to be converted
             * when IO is completed.
             */
            ext4_inode_aio_set(inode, io_end);
        }

        if (overwrite)
            ret = __blockdev_direct_IO(rw, iocb, inode,
                         inode->i_sb->s_bdev, iov,
                         offset, nr_segs,
                         ext4_get_block_write_nolock,
                         ext4_end_io_dio,
                         NULL,
                         0);
        else
            ret = __blockdev_direct_IO(rw, iocb, inode,
                         inode->i_sb->s_bdev, iov,
                         offset, nr_segs,
                         ext4_get_block_write,
                         ext4_end_io_dio,
                         NULL,
                         DIO_LOCKING);
        if (iocb->private)
            ext4_inode_aio_set(inode, NULL);
        /*
         * The io_end structure takes a reference to the inode,
         * that structure needs to be destroyed and the
         * reference to the inode need to be dropped, when IO is
         * complete, even with 0 byte write, or failed.
         *
         * In the successful AIO DIO case, the io_end structure will be
         * desctroyed and the reference to the inode will be dropped
         * after the end_io call back function is called.
         *
         * In the case there is 0 byte write, or error case, since
         * VFS direct IO won't invoke the end_io call back function,
         * we need to free the end_io structure here.
         */
        if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
            ext4_free_io_end(iocb->private);
            iocb->private = NULL;
        } else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
                        EXT4_STATE_DIO_UNWRITTEN)) {
            int err;
            /*
             * for non AIO case, since the IO is already
             * completed, we could do the conversion right here
             */
            err = ext4_convert_unwritten_extents(inode,
                                 offset, ret);
            if (err < 0)
                ret = err;
            ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
        }

    retake_lock:
        /* take i_mutex locking again if we do a ovewrite dio */
        if (overwrite) {
            inode_dio_done(inode);
            up_read(&EXT4_I(inode)->i_data_sem);
            mutex_lock(&inode->i_mutex);
        }

        return ret;
    }

    /* for write the the end of file case, we fall back to old way */
    return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
}

static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
                  const struct iovec *iov, loff_t offset,
                  unsigned long nr_segs)
{
    struct file *file = iocb->ki_filp;
    struct inode *inode = file->f_mapping->host;
    ssize_t ret;

    /*
     * If we are doing data journalling we don't support O_DIRECT
     */
    if (ext4_should_journal_data(inode))
        return 0;

    trace_ext4_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw);
    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
        ret = ext4_ext_direct_IO(rw, iocb, iov, offset, nr_segs);
    else
        ret = ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
    trace_ext4_direct_IO_exit(inode, offset,
                iov_length(iov, nr_segs), rw, ret);
    return ret;
}

/*
 * Pages can be marked dirty completely asynchronously from ext4's journalling
 * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
 * much here because ->set_page_dirty is called under VFS locks.  The page is
 * not necessarily locked.
 *
 * We cannot just dirty the page and leave attached buffers clean, because the
 * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
 * or jbddirty because all the journalling code will explode.
 *
 * So what we do is to mark the page "pending dirty" and next time writepage
 * is called, propagate that into the buffers appropriately.
 */
static int ext4_journalled_set_page_dirty(struct page *page)
{
    SetPageChecked(page);
    return __set_page_dirty_nobuffers(page);
}

static const struct address_space_operations ext4_ordered_aops = {
    .readpage       = ext4_readpage,
    .readpages      = ext4_readpages,
    .writepage      = ext4_writepage,
    .write_begin        = ext4_write_begin,
    .write_end      = ext4_ordered_write_end,
    .bmap           = ext4_bmap,
    .invalidatepage     = ext4_invalidatepage,
    .releasepage        = ext4_releasepage,
    .direct_IO      = ext4_direct_IO,
    .migratepage        = buffer_migrate_page,
    .is_partially_uptodate  = block_is_partially_uptodate,
    .error_remove_page  = generic_error_remove_page,
};

static const struct address_space_operations ext4_writeback_aops = {
    .readpage       = ext4_readpage,
    .readpages      = ext4_readpages,
    .writepage      = ext4_writepage,
    .write_begin        = ext4_write_begin,
    .write_end      = ext4_writeback_write_end,
    .bmap           = ext4_bmap,
    .invalidatepage     = ext4_invalidatepage,
    .releasepage        = ext4_releasepage,
    .direct_IO      = ext4_direct_IO,
    .migratepage        = buffer_migrate_page,
    .is_partially_uptodate  = block_is_partially_uptodate,
    .error_remove_page  = generic_error_remove_page,
};

static const struct address_space_operations ext4_journalled_aops = {
    .readpage       = ext4_readpage,
    .readpages      = ext4_readpages,
    .writepage      = ext4_writepage,
    .write_begin        = ext4_write_begin,
    .write_end      = ext4_journalled_write_end,
    .set_page_dirty     = ext4_journalled_set_page_dirty,
    .bmap           = ext4_bmap,
    .invalidatepage     = ext4_invalidatepage,
    .releasepage        = ext4_releasepage,
    .direct_IO      = ext4_direct_IO,
    .is_partially_uptodate  = block_is_partially_uptodate,
    .error_remove_page  = generic_error_remove_page,
};

static const struct address_space_operations ext4_da_aops = {
    .readpage       = ext4_readpage,
    .readpages      = ext4_readpages,
    .writepage      = ext4_writepage,
    .writepages     = ext4_da_writepages,
    .write_begin        = ext4_da_write_begin,
    .write_end      = ext4_da_write_end,
    .bmap           = ext4_bmap,
    .invalidatepage     = ext4_da_invalidatepage,
    .releasepage        = ext4_releasepage,
    .direct_IO      = ext4_direct_IO,
    .migratepage        = buffer_migrate_page,
    .is_partially_uptodate  = block_is_partially_uptodate,
    .error_remove_page  = generic_error_remove_page,
};

void ext4_set_aops(struct inode *inode)
{
    switch (ext4_inode_journal_mode(inode)) {
    case EXT4_INODE_ORDERED_DATA_MODE:
        if (test_opt(inode->i_sb, DELALLOC))
            inode->i_mapping->a_ops = &ext4_da_aops;
        else
            inode->i_mapping->a_ops = &ext4_ordered_aops;
        break;
    case EXT4_INODE_WRITEBACK_DATA_MODE:
        if (test_opt(inode->i_sb, DELALLOC))
            inode->i_mapping->a_ops = &ext4_da_aops;
        else
            inode->i_mapping->a_ops = &ext4_writeback_aops;
        break;
    case EXT4_INODE_JOURNAL_DATA_MODE:
        inode->i_mapping->a_ops = &ext4_journalled_aops;
        break;
    default:
        BUG();
    }
}


/*
 * ext4_discard_partial_page_buffers()
 * Wrapper function for ext4_discard_partial_page_buffers_no_lock.
 * This function finds and locks the page containing the offset
 * "from" and passes it to ext4_discard_partial_page_buffers_no_lock.
 * Calling functions that already have the page locked should call
 * ext4_discard_partial_page_buffers_no_lock directly.
 */
int ext4_discard_partial_page_buffers(handle_t *handle,
        struct address_space *mapping, loff_t from,
        loff_t length, int flags)
{
    struct inode *inode = mapping->host;
    struct page *page;
    int err = 0;

    page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
                   mapping_gfp_mask(mapping) & ~__GFP_FS);
    if (!page)
        return -ENOMEM;

    err = ext4_discard_partial_page_buffers_no_lock(handle, inode, page,
        from, length, flags);

    unlock_page(page);
    page_cache_release(page);
    return err;
}

/*
 * ext4_discard_partial_page_buffers_no_lock()
 * Zeros a page range of length 'length' starting from offset 'from'.
 * Buffer heads that correspond to the block aligned regions of the
 * zeroed range will be unmapped.  Unblock aligned regions
 * will have the corresponding buffer head mapped if needed so that
 * that region of the page can be updated with the partial zero out.
 *
 * This function assumes that the page has already been  locked.  The
 * The range to be discarded must be contained with in the given page.
 * If the specified range exceeds the end of the page it will be shortened
 * to the end of the page that corresponds to 'from'.  This function is
 * appropriate for updating a page and it buffer heads to be unmapped and
 * zeroed for blocks that have been either released, or are going to be
 * released.
 *
 * handle: The journal handle
 * inode:  The files inode
 * page:   A locked page that contains the offset "from"
 * from:   The starting byte offset (from the beginning of the file)
 *         to begin discarding
 * len:    The length of bytes to discard
 * flags:  Optional flags that may be used:
 *
 *         EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED
 *         Only zero the regions of the page whose buffer heads
 *         have already been unmapped.  This flag is appropriate
 *         for updating the contents of a page whose blocks may
 *         have already been released, and we only want to zero
 *         out the regions that correspond to those released blocks.
 *
 * Returns zero on success or negative on failure.
 */
static int ext4_discard_partial_page_buffers_no_lock(handle_t *handle,
        struct inode *inode, struct page *page, loff_t from,
        loff_t length, int flags)
{
    ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
    unsigned int offset = from & (PAGE_CACHE_SIZE-1);
    unsigned int blocksize, max, pos;
    ext4_lblk_t iblock;
    struct buffer_head *bh;
    int err = 0;

    blocksize = inode->i_sb->s_blocksize;
    max = PAGE_CACHE_SIZE - offset;

    if (index != page->index)
        return -EINVAL;

    /*
     * correct length if it does not fall between
     * 'from' and the end of the page
     */
    if (length > max || length < 0)
        length = max;

    iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

    if (!page_has_buffers(page))
        create_empty_buffers(page, blocksize, 0);

    /* Find the buffer that contains "offset" */
    bh = page_buffers(page);
    pos = blocksize;
    while (offset >= pos) {
        bh = bh->b_this_page;
        iblock++;
        pos += blocksize;
    }

    pos = offset;
    while (pos < offset + length) {
        unsigned int end_of_block, range_to_discard;

        err = 0;

        /* The length of space left to zero and unmap */
        range_to_discard = offset + length - pos;

        /* The length of space until the end of the block */
        end_of_block = blocksize - (pos & (blocksize-1));

        /*
         * Do not unmap or zero past end of block
         * for this buffer head
         */
        if (range_to_discard > end_of_block)
            range_to_discard = end_of_block;


        /*
         * Skip this buffer head if we are only zeroing unampped
         * regions of the page
         */
        if (flags & EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED &&
            buffer_mapped(bh))
                goto next;

        /* If the range is block aligned, unmap */
        if (range_to_discard == blocksize) {
            clear_buffer_dirty(bh);
            bh->b_bdev = NULL;
            clear_buffer_mapped(bh);
            clear_buffer_req(bh);
            clear_buffer_new(bh);
            clear_buffer_delay(bh);
            clear_buffer_unwritten(bh);
            clear_buffer_uptodate(bh);
            zero_user(page, pos, range_to_discard);
            BUFFER_TRACE(bh, "Buffer discarded");
            goto next;
        }

        /*
         * If this block is not completely contained in the range
         * to be discarded, then it is not going to be released. Because
         * we need to keep this block, we need to make sure this part
         * of the page is uptodate before we modify it by writeing
         * partial zeros on it.
         */
        if (!buffer_mapped(bh)) {
            /*
             * Buffer head must be mapped before we can read
             * from the block
             */
            BUFFER_TRACE(bh, "unmapped");
            ext4_get_block(inode, iblock, bh, 0);
            /* unmapped? It's a hole - nothing to do */
            if (!buffer_mapped(bh)) {
                BUFFER_TRACE(bh, "still unmapped");
                goto next;
            }
        }

        /* Ok, it's mapped. Make sure it's up-to-date */
        if (PageUptodate(page))
            set_buffer_uptodate(bh);

        if (!buffer_uptodate(bh)) {
            err = -EIO;
            ll_rw_block(READ, 1, &bh);
            wait_on_buffer(bh);
            /* Uhhuh. Read error. Complain and punt.*/
            if (!buffer_uptodate(bh))
                goto next;
        }

        if (ext4_should_journal_data(inode)) {
            BUFFER_TRACE(bh, "get write access");
            err = ext4_journal_get_write_access(handle, bh);
            if (err)
                goto next;
        }

        zero_user(page, pos, range_to_discard);

        err = 0;
        if (ext4_should_journal_data(inode)) {
            err = ext4_handle_dirty_metadata(handle, inode, bh);
        } else
            mark_buffer_dirty(bh);

        BUFFER_TRACE(bh, "Partial buffer zeroed");
next:
        bh = bh->b_this_page;
        iblock++;
        pos += range_to_discard;
    }

    return err;
}

int ext4_can_truncate(struct inode *inode)
{
    if (S_ISREG(inode->i_mode))
        return 1;
    if (S_ISDIR(inode->i_mode))
        return 1;
    if (S_ISLNK(inode->i_mode))
        return !ext4_inode_is_fast_symlink(inode);
    return 0;
}

/*
 * ext4_punch_hole: punches a hole in a file by releaseing the blocks
 * associated with the given offset and length
 *
 * @inode:  File inode
 * @offset: The offset where the hole will begin
 * @len:    The length of the hole
 *
 * Returns: 0 on success or negative on failure
 */

int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    if (!S_ISREG(inode->i_mode))
        return -EOPNOTSUPP;

    if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
        /* TODO: Add support for non extent hole punching */
        return -EOPNOTSUPP;
    }

    if (EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) {
        /* TODO: Add support for bigalloc file systems */
        return -EOPNOTSUPP;
    }

    return ext4_ext_punch_hole(file, offset, length);
}

/*
 * ext4_truncate()
 *
 * We block out ext4_get_block() block instantiations across the entire
 * transaction, and VFS/VM ensures that ext4_truncate() cannot run
 * simultaneously on behalf of the same inode.
 *
 * As we work through the truncate and commit bits of it to the journal there
 * is one core, guiding principle: the file's tree must always be consistent on
 * disk.  We must be able to restart the truncate after a crash.
 *
 * The file's tree may be transiently inconsistent in memory (although it
 * probably isn't), but whenever we close off and commit a journal transaction,
 * the contents of (the filesystem + the journal) must be consistent and
 * restartable.  It's pretty simple, really: bottom up, right to left (although
 * left-to-right works OK too).
 *
 * Note that at recovery time, journal replay occurs *before* the restart of
 * truncate against the orphan inode list.
 *
 * The committed inode has the new, desired i_size (which is the same as
 * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
 * that this inode's truncate did not complete and it will again call
 * ext4_truncate() to have another go.  So there will be instantiated blocks
 * to the right of the truncation point in a crashed ext4 filesystem.  But
 * that's fine - as long as they are linked from the inode, the post-crash
 * ext4_truncate() run will find them and release them.
 */
void ext4_truncate(struct inode *inode)
{
    trace_ext4_truncate_enter(inode);

    if (!ext4_can_truncate(inode))
        return;

    ext4_clear_inode_flag(inode, EXT4_INODE_EOFBLOCKS);

    if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
        ext4_set_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE);

    if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
        ext4_ext_truncate(inode);
    else
        ext4_ind_truncate(inode);

    trace_ext4_truncate_exit(inode);
}

/*
 * ext4_get_inode_loc returns with an extra refcount against the inode's
 * underlying buffer_head on success. If 'in_mem' is true, we have all
 * data in memory that is needed to recreate the on-disk version of this
 * inode.
 */
static int __ext4_get_inode_loc(struct inode *inode,
                struct ext4_iloc *iloc, int in_mem)
{
    struct ext4_group_desc  *gdp;
    struct buffer_head  *bh;
    struct super_block  *sb = inode->i_sb;
    ext4_fsblk_t        block;
    int         inodes_per_block, inode_offset;

    iloc->bh = NULL;
    if (!ext4_valid_inum(sb, inode->i_ino))
        return -EIO;

    iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
    gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
    if (!gdp)
        return -EIO;

    /*
     * Figure out the offset within the block group inode table
     */
    inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
    inode_offset = ((inode->i_ino - 1) %
            EXT4_INODES_PER_GROUP(sb));
    block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
    iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);

    bh = sb_getblk(sb, block);
    if (!bh) {
        EXT4_ERROR_INODE_BLOCK(inode, block,
                       "unable to read itable block");
        return -EIO;
    }
    if (!buffer_uptodate(bh)) {
        lock_buffer(bh);

        /*
         * If the buffer has the write error flag, we have failed
         * to write out another inode in the same block.  In this
         * case, we don't have to read the block because we may
         * read the old inode data successfully.
         */
        if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
            set_buffer_uptodate(bh);

        if (buffer_uptodate(bh)) {
            /* someone brought it uptodate while we waited */
            unlock_buffer(bh);
            goto has_buffer;
        }

        /*
         * If we have all information of the inode in memory and this
         * is the only valid inode in the block, we need not read the
         * block.
         */
        if (in_mem) {
            struct buffer_head *bitmap_bh;
            int i, start;

            start = inode_offset & ~(inodes_per_block - 1);

            /* Is the inode bitmap in cache? */
            bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
            if (!bitmap_bh)
                goto make_io;

            /*
             * If the inode bitmap isn't in cache then the
             * optimisation may end up performing two reads instead
             * of one, so skip it.
             */
            if (!buffer_uptodate(bitmap_bh)) {
                brelse(bitmap_bh);
                goto make_io;
            }
            for (i = start; i < start + inodes_per_block; i++) {
                if (i == inode_offset)
                    continue;
                if (ext4_test_bit(i, bitmap_bh->b_data))
                    break;
            }
            brelse(bitmap_bh);
            if (i == start + inodes_per_block) {
                /* all other inodes are free, so skip I/O */
                memset(bh->b_data, 0, bh->b_size);
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
                goto has_buffer;
            }
        }

make_io:
        /*
         * If we need to do any I/O, try to pre-readahead extra
         * blocks from the inode table.
         */
        if (EXT4_SB(sb)->s_inode_readahead_blks) {
            ext4_fsblk_t b, end, table;
            unsigned num;

            table = ext4_inode_table(sb, gdp);
            /* s_inode_readahead_blks is always a power of 2 */
            b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
            if (table > b)
                b = table;
            end = b + EXT4_SB(sb)->s_inode_readahead_blks;
            num = EXT4_INODES_PER_GROUP(sb);
            if (ext4_has_group_desc_csum(sb))
                num -= ext4_itable_unused_count(sb, gdp);
            table += num / inodes_per_block;
            if (end > table)
                end = table;
            while (b <= end)
                sb_breadahead(sb, b++);
        }

        /*
         * There are other valid inodes in the buffer, this inode
         * has in-inode xattrs, or we don't have this inode in memory.
         * Read the block from disk.
         */
        trace_ext4_load_inode(inode);
        get_bh(bh);
        bh->b_end_io = end_buffer_read_sync;
        submit_bh(READ | REQ_META | REQ_PRIO, bh);
        wait_on_buffer(bh);
        if (!buffer_uptodate(bh)) {
            EXT4_ERROR_INODE_BLOCK(inode, block,
                           "unable to read itable block");
            brelse(bh);
            return -EIO;
        }
    }
has_buffer:
    iloc->bh = bh;
    return 0;
}

int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
{
    /* We have all inode data except xattrs in memory here. */
    return __ext4_get_inode_loc(inode, iloc,
        !ext4_test_inode_state(inode, EXT4_STATE_XATTR));
}

void ext4_set_inode_flags(struct inode *inode)
{
    unsigned int flags = EXT4_I(inode)->i_flags;

    inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
    if (flags & EXT4_SYNC_FL)
        inode->i_flags |= S_SYNC;
    if (flags & EXT4_APPEND_FL)
        inode->i_flags |= S_APPEND;
    if (flags & EXT4_IMMUTABLE_FL)
        inode->i_flags |= S_IMMUTABLE;
    if (flags & EXT4_NOATIME_FL)
        inode->i_flags |= S_NOATIME;
    if (flags & EXT4_DIRSYNC_FL)
        inode->i_flags |= S_DIRSYNC;
}

/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
void ext4_get_inode_flags(struct ext4_inode_info *ei)
{
    unsigned int vfs_fl;
    unsigned long old_fl, new_fl;

    do {
        vfs_fl = ei->vfs_inode.i_flags;
        old_fl = ei->i_flags;
        new_fl = old_fl & ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
                EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|
                EXT4_DIRSYNC_FL);
        if (vfs_fl & S_SYNC)
            new_fl |= EXT4_SYNC_FL;
        if (vfs_fl & S_APPEND)
            new_fl |= EXT4_APPEND_FL;
        if (vfs_fl & S_IMMUTABLE)
            new_fl |= EXT4_IMMUTABLE_FL;
        if (vfs_fl & S_NOATIME)
            new_fl |= EXT4_NOATIME_FL;
        if (vfs_fl & S_DIRSYNC)
            new_fl |= EXT4_DIRSYNC_FL;
    } while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl);
}

static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
                  struct ext4_inode_info *ei)
{
    blkcnt_t i_blocks ;
    struct inode *inode = &(ei->vfs_inode);
    struct super_block *sb = inode->i_sb;

    if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
        /* we are using combined 48 bit field */
        i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
                    le32_to_cpu(raw_inode->i_blocks_lo);
        if (ext4_test_inode_flag(inode, EXT4_INODE_HUGE_FILE)) {
            /* i_blocks represent file system block size */
            return i_blocks  << (inode->i_blkbits - 9);
        } else {
            return i_blocks;
        }
    } else {
        return le32_to_cpu(raw_inode->i_blocks_lo);
    }
}

struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
{
    struct ext4_iloc iloc;
    struct ext4_inode *raw_inode;
    struct ext4_inode_info *ei;
    struct inode *inode;
    journal_t *journal = EXT4_SB(sb)->s_journal;
    long ret;
    int block;
    uid_t i_uid;
    gid_t i_gid;

    inode = iget_locked(sb, ino);
    if (!inode)
        return ERR_PTR(-ENOMEM);
    if (!(inode->i_state & I_NEW))
        return inode;

    ei = EXT4_I(inode);
    iloc.bh = NULL;

    ret = __ext4_get_inode_loc(inode, &iloc, 0);
    if (ret < 0)
        goto bad_inode;
    raw_inode = ext4_raw_inode(&iloc);

    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
        ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
        if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
            EXT4_INODE_SIZE(inode->i_sb)) {
            EXT4_ERROR_INODE(inode, "bad extra_isize (%u != %u)",
                EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize,
                EXT4_INODE_SIZE(inode->i_sb));
            ret = -EIO;
            goto bad_inode;
        }
    } else
        ei->i_extra_isize = 0;

    /* Precompute checksum seed for inode metadata */
    if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
            EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        __u32 csum;
        __le32 inum = cpu_to_le32(inode->i_ino);
        __le32 gen = raw_inode->i_generation;
        csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)&inum,
                   sizeof(inum));
        ei->i_csum_seed = ext4_chksum(sbi, csum, (__u8 *)&gen,
                          sizeof(gen));
    }

    if (!ext4_inode_csum_verify(inode, raw_inode, ei)) {
        EXT4_ERROR_INODE(inode, "checksum invalid");
        ret = -EIO;
        goto bad_inode;
    }

    inode->i_mode = le16_to_cpu(raw_inode->i_mode);
    i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
    i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
    if (!(test_opt(inode->i_sb, NO_UID32))) {
        i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
        i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
    }
    i_uid_write(inode, i_uid);
    i_gid_write(inode, i_gid);
    set_nlink(inode, le16_to_cpu(raw_inode->i_links_count));

    ext4_clear_state_flags(ei); /* Only relevant on 32-bit archs */
    ei->i_dir_start_lookup = 0;
    ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
    /* We now have enough fields to check if the inode was active or not.
     * This is needed because nfsd might try to access dead inodes
     * the test is that same one that e2fsck uses
     * NeilBrown 1999oct15
     */
    if (inode->i_nlink == 0) {
        if (inode->i_mode == 0 ||
            !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
            /* this inode is deleted */
            ret = -ESTALE;
            goto bad_inode;
        }
        /* The only unlinked inodes we let through here have
         * valid i_mode and are being read by the orphan
         * recovery code: that's fine, we're about to complete
         * the process of deleting those. */
    }
    ei->i_flags = le32_to_cpu(raw_inode->i_flags);
    inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
    ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
    if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_64BIT))
        ei->i_file_acl |=
            ((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
    inode->i_size = ext4_isize(raw_inode);
    ei->i_disksize = inode->i_size;
#ifdef CONFIG_QUOTA
    ei->i_reserved_quota = 0;
#endif
    inode->i_generation = le32_to_cpu(raw_inode->i_generation);
    ei->i_block_group = iloc.block_group;
    ei->i_last_alloc_group = ~0;
    /*
     * NOTE! The in-memory inode i_data array is in little-endian order
     * even on big-endian machines: we do NOT byteswap the block numbers!
     */
    for (block = 0; block < EXT4_N_BLOCKS; block++)
        ei->i_data[block] = raw_inode->i_block[block];
    INIT_LIST_HEAD(&ei->i_orphan);

    /*
     * Set transaction id's of transactions that have to be committed
     * to finish f[data]sync. We set them to currently running transaction
     * as we cannot be sure that the inode or some of its metadata isn't
     * part of the transaction - the inode could have been reclaimed and
     * now it is reread from disk.
     */
    if (journal) {
        transaction_t *transaction;
        tid_t tid;

        read_lock(&journal->j_state_lock);
        if (journal->j_running_transaction)
            transaction = journal->j_running_transaction;
        else
            transaction = journal->j_committing_transaction;
        if (transaction)
            tid = transaction->t_tid;
        else
            tid = journal->j_commit_sequence;
        read_unlock(&journal->j_state_lock);
        ei->i_sync_tid = tid;
        ei->i_datasync_tid = tid;
    }

    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
        if (ei->i_extra_isize == 0) {
            /* The extra space is currently unused. Use it. */
            ei->i_extra_isize = sizeof(struct ext4_inode) -
                        EXT4_GOOD_OLD_INODE_SIZE;
        } else {
            __le32 *magic = (void *)raw_inode +
                    EXT4_GOOD_OLD_INODE_SIZE +
                    ei->i_extra_isize;
            if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC))
                ext4_set_inode_state(inode, EXT4_STATE_XATTR);
        }
    }

    EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
    EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
    EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
    EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);

    inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
        if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
            inode->i_version |=
            (__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
    }

    ret = 0;
    if (ei->i_file_acl &&
        !ext4_data_block_valid(EXT4_SB(sb), ei->i_file_acl, 1)) {
        EXT4_ERROR_INODE(inode, "bad extended attribute block %llu",
                 ei->i_file_acl);
        ret = -EIO;
        goto bad_inode;
    } else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
        if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
            (S_ISLNK(inode->i_mode) &&
             !ext4_inode_is_fast_symlink(inode)))
            /* Validate extent which is part of inode */
            ret = ext4_ext_check_inode(inode);
    } else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
           (S_ISLNK(inode->i_mode) &&
            !ext4_inode_is_fast_symlink(inode))) {
        /* Validate block references which are part of inode */
        ret = ext4_ind_check_inode(inode);
    }
    if (ret)
        goto bad_inode;

    if (S_ISREG(inode->i_mode)) {
        inode->i_op = &ext4_file_inode_operations;
        inode->i_fop = &ext4_file_operations;
        ext4_set_aops(inode);
    } else if (S_ISDIR(inode->i_mode)) {
        inode->i_op = &ext4_dir_inode_operations;
        inode->i_fop = &ext4_dir_operations;
    } else if (S_ISLNK(inode->i_mode)) {
        if (ext4_inode_is_fast_symlink(inode)) {
            inode->i_op = &ext4_fast_symlink_inode_operations;
            nd_terminate_link(ei->i_data, inode->i_size,
                sizeof(ei->i_data) - 1);
        } else {
            inode->i_op = &ext4_symlink_inode_operations;
            ext4_set_aops(inode);
        }
    } else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
          S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
        inode->i_op = &ext4_special_inode_operations;
        if (raw_inode->i_block[0])
            init_special_inode(inode, inode->i_mode,
               old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
        else
            init_special_inode(inode, inode->i_mode,
               new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
    } else {
        ret = -EIO;
        EXT4_ERROR_INODE(inode, "bogus i_mode (%o)", inode->i_mode);
        goto bad_inode;
    }
    brelse(iloc.bh);
    ext4_set_inode_flags(inode);
    unlock_new_inode(inode);
    return inode;

bad_inode:
    brelse(iloc.bh);
    iget_failed(inode);
    return ERR_PTR(ret);
}

static int ext4_inode_blocks_set(handle_t *handle,
                struct ext4_inode *raw_inode,
                struct ext4_inode_info *ei)
{
    struct inode *inode = &(ei->vfs_inode);
    u64 i_blocks = inode->i_blocks;
    struct super_block *sb = inode->i_sb;

    if (i_blocks <= ~0U) {
        /*
         * i_blocks can be represented in a 32 bit variable
         * as multiple of 512 bytes
         */
        raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
        raw_inode->i_blocks_high = 0;
        ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
        return 0;
    }
    if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE))
        return -EFBIG;

    if (i_blocks <= 0xffffffffffffULL) {
        /*
         * i_blocks can be represented in a 48 bit variable
         * as multiple of 512 bytes
         */
        raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
        raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
        ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
    } else {
        ext4_set_inode_flag(inode, EXT4_INODE_HUGE_FILE);
        /* i_block is stored in file system block size */
        i_blocks = i_blocks >> (inode->i_blkbits - 9);
        raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
        raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
    }
    return 0;
}

/*
 * Post the struct inode info into an on-disk inode location in the
 * buffer-cache.  This gobbles the caller's reference to the
 * buffer_head in the inode location struct.
 *
 * The caller must have write access to iloc->bh.
 */
static int ext4_do_update_inode(handle_t *handle,
                struct inode *inode,
                struct ext4_iloc *iloc)
{
    struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
    struct ext4_inode_info *ei = EXT4_I(inode);
    struct buffer_head *bh = iloc->bh;
    int err = 0, rc, block;
    int need_datasync = 0;
    uid_t i_uid;
    gid_t i_gid;

    /* For fields not not tracking in the in-memory inode,
     * initialise them to zero for new inodes. */
    if (ext4_test_inode_state(inode, EXT4_STATE_NEW))
        memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);

    ext4_get_inode_flags(ei);
    raw_inode->i_mode = cpu_to_le16(inode->i_mode);
    i_uid = i_uid_read(inode);
    i_gid = i_gid_read(inode);
    if (!(test_opt(inode->i_sb, NO_UID32))) {
        raw_inode->i_uid_low = cpu_to_le16(low_16_bits(i_uid));
        raw_inode->i_gid_low = cpu_to_le16(low_16_bits(i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
        if (!ei->i_dtime) {
            raw_inode->i_uid_high =
                cpu_to_le16(high_16_bits(i_uid));
            raw_inode->i_gid_high =
                cpu_to_le16(high_16_bits(i_gid));
        } else {
            raw_inode->i_uid_high = 0;
            raw_inode->i_gid_high = 0;
        }
    } else {
        raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(i_uid));
        raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(i_gid));
        raw_inode->i_uid_high = 0;
        raw_inode->i_gid_high = 0;
    }
    raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);

    EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
    EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
    EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
    EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);

    if (ext4_inode_blocks_set(handle, raw_inode, ei))
        goto out_brelse;
    raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
    raw_inode->i_flags = cpu_to_le32(ei->i_flags & 0xFFFFFFFF);
    if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
        cpu_to_le32(EXT4_OS_HURD))
        raw_inode->i_file_acl_high =
            cpu_to_le16(ei->i_file_acl >> 32);
    raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
    if (ei->i_disksize != ext4_isize(raw_inode)) {
        ext4_isize_set(raw_inode, ei->i_disksize);
        need_datasync = 1;
    }
    if (ei->i_disksize > 0x7fffffffULL) {
        struct super_block *sb = inode->i_sb;
        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
                EXT4_SB(sb)->s_es->s_rev_level ==
                cpu_to_le32(EXT4_GOOD_OLD_REV)) {
            /* If this is the first large file
             * created, add a flag to the superblock.
             */
            err = ext4_journal_get_write_access(handle,
                    EXT4_SB(sb)->s_sbh);
            if (err)
                goto out_brelse;
            ext4_update_dynamic_rev(sb);
            EXT4_SET_RO_COMPAT_FEATURE(sb,
                    EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
            ext4_handle_sync(handle);
            err = ext4_handle_dirty_super(handle, sb);
        }
    }
    raw_inode->i_generation = cpu_to_le32(inode->i_generation);
    if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
        if (old_valid_dev(inode->i_rdev)) {
            raw_inode->i_block[0] =
                cpu_to_le32(old_encode_dev(inode->i_rdev));
            raw_inode->i_block[1] = 0;
        } else {
            raw_inode->i_block[0] = 0;
            raw_inode->i_block[1] =
                cpu_to_le32(new_encode_dev(inode->i_rdev));
            raw_inode->i_block[2] = 0;
        }
    } else
        for (block = 0; block < EXT4_N_BLOCKS; block++)
            raw_inode->i_block[block] = ei->i_data[block];

    raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
    if (ei->i_extra_isize) {
        if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
            raw_inode->i_version_hi =
            cpu_to_le32(inode->i_version >> 32);
        raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
    }

    ext4_inode_csum_set(inode, raw_inode, ei);

    BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
    rc = ext4_handle_dirty_metadata(handle, NULL, bh);
    if (!err)
        err = rc;
    ext4_clear_inode_state(inode, EXT4_STATE_NEW);

    ext4_update_inode_fsync_trans(handle, inode, need_datasync);
out_brelse:
    brelse(bh);
    ext4_std_error(inode->i_sb, err);
    return err;
}

/*
 * ext4_write_inode()
 *
 * We are called from a few places:
 *
 * - Within generic_file_write() for O_SYNC files.
 *   Here, there will be no transaction running. We wait for any running
 *   transaction to commit.
 *
 * - Within sys_sync(), kupdate and such.
 *   We wait on commit, if tol to.
 *
 * - Within prune_icache() (PF_MEMALLOC == true)
 *   Here we simply return.  We can't afford to block kswapd on the
 *   journal commit.
 *
 * In all cases it is actually safe for us to return without doing anything,
 * because the inode has been copied into a raw inode buffer in
 * ext4_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
 * knfsd.
 *
 * Note that we are absolutely dependent upon all inode dirtiers doing the
 * right thing: they *must* call mark_inode_dirty() after dirtying info in
 * which we are interested.
 *
 * It would be a bug for them to not do this.  The code:
 *
 *  mark_inode_dirty(inode)
 *  stuff();
 *  inode->i_size = expr;
 *
 * is in error because a kswapd-driven write_inode() could occur while
 * `stuff()' is running, and the new i_size will be lost.  Plus the inode
 * will no longer be on the superblock's dirty inode list.
 */
int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
{
    int err;

    if (current->flags & PF_MEMALLOC)
        return 0;

    if (EXT4_SB(inode->i_sb)->s_journal) {
        if (ext4_journal_current_handle()) {
            jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
            dump_stack();
            return -EIO;
        }

        if (wbc->sync_mode != WB_SYNC_ALL)
            return 0;

        err = ext4_force_commit(inode->i_sb);
    } else {
        struct ext4_iloc iloc;

        err = __ext4_get_inode_loc(inode, &iloc, 0);
        if (err)
            return err;
        if (wbc->sync_mode == WB_SYNC_ALL)
            sync_dirty_buffer(iloc.bh);
        if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) {
            EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr,
                     "IO error syncing inode");
            err = -EIO;
        }
        brelse(iloc.bh);
    }
    return err;
}

/*
 * ext4_setattr()
 *
 * Called from notify_change.
 *
 * We want to trap VFS attempts to truncate the file as soon as
 * possible.  In particular, we want to make sure that when the VFS
 * shrinks i_size, we put the inode on the orphan list and modify
 * i_disksize immediately, so that during the subsequent flushing of
 * dirty pages and freeing of disk blocks, we can guarantee that any
 * commit will leave the blocks being flushed in an unused state on
 * disk.  (On recovery, the inode will get truncated and the blocks will
 * be freed, so we have a strong guarantee that no future commit will
 * leave these blocks visible to the user.)
 *
 * Another thing we have to assure is that if we are in ordered mode
 * and inode is still attached to the committing transaction, we must
 * we start writeout of all the dirty pages which are being truncated.
 * This way we are sure that all the data written in the previous
 * transaction are already on disk (truncate waits for pages under
 * writeback).
 *
 * Called with inode->i_mutex down.
 */
int ext4_setattr(struct dentry *dentry, struct iattr *attr)
{
    struct inode *inode = dentry->d_inode;
    int error, rc = 0;
    int orphan = 0;
    const unsigned int ia_valid = attr->ia_valid;

    error = inode_change_ok(inode, attr);
    if (error)
        return error;

    if (is_quota_modification(inode, attr))
        dquot_initialize(inode);
    if ((ia_valid & ATTR_UID && !uid_eq(attr->ia_uid, inode->i_uid)) ||
        (ia_valid & ATTR_GID && !gid_eq(attr->ia_gid, inode->i_gid))) {
        handle_t *handle;

        /* (user+group)*(old+new) structure, inode write (sb,
         * inode block, ? - but truncate inode update has it) */
        handle = ext4_journal_start(inode, (EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb)+
                    EXT4_MAXQUOTAS_DEL_BLOCKS(inode->i_sb))+3);
        if (IS_ERR(handle)) {
            error = PTR_ERR(handle);
            goto err_out;
        }
        error = dquot_transfer(inode, attr);
        if (error) {
            ext4_journal_stop(handle);
            return error;
        }
        /* Update corresponding info in inode so that everything is in
         * one transaction */
        if (attr->ia_valid & ATTR_UID)
            inode->i_uid = attr->ia_uid;
        if (attr->ia_valid & ATTR_GID)
            inode->i_gid = attr->ia_gid;
        error = ext4_mark_inode_dirty(handle, inode);
        ext4_journal_stop(handle);
    }

    if (attr->ia_valid & ATTR_SIZE) {

        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
            struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

            if (attr->ia_size > sbi->s_bitmap_maxbytes)
                return -EFBIG;
        }
    }

    if (S_ISREG(inode->i_mode) &&
        attr->ia_valid & ATTR_SIZE &&
        (attr->ia_size < inode->i_size)) {
        handle_t *handle;

        handle = ext4_journal_start(inode, 3);
        if (IS_ERR(handle)) {
            error = PTR_ERR(handle);
            goto err_out;
        }
        if (ext4_handle_valid(handle)) {
            error = ext4_orphan_add(handle, inode);
            orphan = 1;
        }
        EXT4_I(inode)->i_disksize = attr->ia_size;
        rc = ext4_mark_inode_dirty(handle, inode);
        if (!error)
            error = rc;
        ext4_journal_stop(handle);

        if (ext4_should_order_data(inode)) {
            error = ext4_begin_ordered_truncate(inode,
                                attr->ia_size);
            if (error) {
                /* Do as much error cleanup as possible */
                handle = ext4_journal_start(inode, 3);
                if (IS_ERR(handle)) {
                    ext4_orphan_del(NULL, inode);
                    goto err_out;
                }
                ext4_orphan_del(handle, inode);
                orphan = 0;
                ext4_journal_stop(handle);
                goto err_out;
            }
        }
    }

    if (attr->ia_valid & ATTR_SIZE) {
        if (attr->ia_size != i_size_read(inode)) {
            truncate_setsize(inode, attr->ia_size);
            /* Inode size will be reduced, wait for dio in flight.
             * Temporarily disable dioread_nolock to prevent
             * livelock. */
            if (orphan) {
                ext4_inode_block_unlocked_dio(inode);
                inode_dio_wait(inode);
                ext4_inode_resume_unlocked_dio(inode);
            }
        }
        ext4_truncate(inode);
    }

    if (!rc) {
        setattr_copy(inode, attr);
        mark_inode_dirty(inode);
    }

    /*
     * If the call to ext4_truncate failed to get a transaction handle at
     * all, we need to clean up the in-core orphan list manually.
     */
    if (orphan && inode->i_nlink)
        ext4_orphan_del(NULL, inode);

    if (!rc && (ia_valid & ATTR_MODE))
        rc = ext4_acl_chmod(inode);

err_out:
    ext4_std_error(inode->i_sb, error);
    if (!error)
        error = rc;
    return error;
}

int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
         struct kstat *stat)
{
    struct inode *inode;
    unsigned long delalloc_blocks;

    inode = dentry->d_inode;
    generic_fillattr(inode, stat);

    /*
     * We can't update i_blocks if the block allocation is delayed
     * otherwise in the case of system crash before the real block
     * allocation is done, we will have i_blocks inconsistent with
     * on-disk file blocks.
     * We always keep i_blocks updated together with real
     * allocation. But to not confuse with user, stat
     * will return the blocks that include the delayed allocation
     * blocks for this file.
     */
    delalloc_blocks = EXT4_C2B(EXT4_SB(inode->i_sb),
                EXT4_I(inode)->i_reserved_data_blocks);

    stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
    return 0;
}

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
    if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
        return ext4_ind_trans_blocks(inode, nrblocks, chunk);
    return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
}

/*
 * Account for index blocks, block groups bitmaps and block group
 * descriptor blocks if modify datablocks and index blocks
 * worse case, the indexs blocks spread over different block groups
 *
 * If datablocks are discontiguous, they are possible to spread over
 * different block groups too. If they are contiguous, with flexbg,
 * they could still across block group boundary.
 *
 * Also account for superblock, inode, quota and xattr blocks
 */
static int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
    ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
    int gdpblocks;
    int idxblocks;
    int ret = 0;

    /*
     * How many index blocks need to touch to modify nrblocks?
     * The "Chunk" flag indicating whether the nrblocks is
     * physically contiguous on disk
     *
     * For Direct IO and fallocate, they calls get_block to allocate
     * one single extent at a time, so they could set the "Chunk" flag
     */
    idxblocks = ext4_index_trans_blocks(inode, nrblocks, chunk);

    ret = idxblocks;

    /*
     * Now let's see how many group bitmaps and group descriptors need
     * to account
     */
    groups = idxblocks;
    if (chunk)
        groups += 1;
    else
        groups += nrblocks;

    gdpblocks = groups;
    if (groups > ngroups)
        groups = ngroups;
    if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
        gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;

    /* bitmaps and block group descriptor blocks */
    ret += groups + gdpblocks;

    /* Blocks for super block, inode, quota and xattr blocks */
    ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);

    return ret;
}

/*
 * Calculate the total number of credits to reserve to fit
 * the modification of a single pages into a single transaction,
 * which may include multiple chunks of block allocations.
 *
 * This could be called via ext4_write_begin()
 *
 * We need to consider the worse case, when
 * one new block per extent.
 */
int ext4_writepage_trans_blocks(struct inode *inode)
{
    int bpp = ext4_journal_blocks_per_page(inode);
    int ret;

    ret = ext4_meta_trans_blocks(inode, bpp, 0);

    /* Account for data blocks for journalled mode */
    if (ext4_should_journal_data(inode))
        ret += bpp;
    return ret;
}

/*
 * Calculate the journal credits for a chunk of data modification.
 *
 * This is called from DIO, fallocate or whoever calling
 * ext4_map_blocks() to map/allocate a chunk of contiguous disk blocks.
 *
 * journal buffers for data blocks are not included here, as DIO
 * and fallocate do no need to journal data buffers.
 */
int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
{
    return ext4_meta_trans_blocks(inode, nrblocks, 1);
}

/*
 * The caller must have previously called ext4_reserve_inode_write().
 * Give this, we know that the caller already has write access to iloc->bh.
 */
int ext4_mark_iloc_dirty(handle_t *handle,
             struct inode *inode, struct ext4_iloc *iloc)
{
    int err = 0;

    if (IS_I_VERSION(inode))
        inode_inc_iversion(inode);

    /* the do_update_inode consumes one bh->b_count */
    get_bh(iloc->bh);

    /* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
    err = ext4_do_update_inode(handle, inode, iloc);
    put_bh(iloc->bh);
    return err;
}

/*
 * On success, We end up with an outstanding reference count against
 * iloc->bh.  This _must_ be cleaned up later.
 */

int
ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
             struct ext4_iloc *iloc)
{
    int err;

    err = ext4_get_inode_loc(inode, iloc);
    if (!err) {
        BUFFER_TRACE(iloc->bh, "get_write_access");
        err = ext4_journal_get_write_access(handle, iloc->bh);
        if (err) {
            brelse(iloc->bh);
            iloc->bh = NULL;
        }
    }
    ext4_std_error(inode->i_sb, err);
    return err;
}

/*
 * Expand an inode by new_extra_isize bytes.
 * Returns 0 on success or negative error number on failure.
 */
static int ext4_expand_extra_isize(struct inode *inode,
                   unsigned int new_extra_isize,
                   struct ext4_iloc iloc,
                   handle_t *handle)
{
    struct ext4_inode *raw_inode;
    struct ext4_xattr_ibody_header *header;

    if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
        return 0;

    raw_inode = ext4_raw_inode(&iloc);

    header = IHDR(inode, raw_inode);

    /* No extended attributes present */
    if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR) ||
        header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
        memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
            new_extra_isize);
        EXT4_I(inode)->i_extra_isize = new_extra_isize;
        return 0;
    }

    /* try to expand with EAs present */
    return ext4_expand_extra_isize_ea(inode, new_extra_isize,
                      raw_inode, handle);
}

/*
 * What we do here is to mark the in-core inode as clean with respect to inode
 * dirtiness (it may still be data-dirty).
 * This means that the in-core inode may be reaped by prune_icache
 * without having to perform any I/O.  This is a very good thing,
 * because *any* task may call prune_icache - even ones which
 * have a transaction open against a different journal.
 *
 * Is this cheating?  Not really.  Sure, we haven't written the
 * inode out, but prune_icache isn't a user-visible syncing function.
 * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
 * we start and wait on commits.
 */
int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
{
    struct ext4_iloc iloc;
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    static unsigned int mnt_count;
    int err, ret;

    might_sleep();
    trace_ext4_mark_inode_dirty(inode, _RET_IP_);
    err = ext4_reserve_inode_write(handle, inode, &iloc);
    if (ext4_handle_valid(handle) &&
        EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
        !ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
        /*
         * We need extra buffer credits since we may write into EA block
         * with this same handle. If journal_extend fails, then it will
         * only result in a minor loss of functionality for that inode.
         * If this is felt to be critical, then e2fsck should be run to
         * force a large enough s_min_extra_isize.
         */
        if ((jbd2_journal_extend(handle,
                 EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
            ret = ext4_expand_extra_isize(inode,
                              sbi->s_want_extra_isize,
                              iloc, handle);
            if (ret) {
                ext4_set_inode_state(inode,
                             EXT4_STATE_NO_EXPAND);
                if (mnt_count !=
                    le16_to_cpu(sbi->s_es->s_mnt_count)) {
                    ext4_warning(inode->i_sb,
                    "Unable to expand inode %lu. Delete"
                    " some EAs or run e2fsck.",
                    inode->i_ino);
                    mnt_count =
                      le16_to_cpu(sbi->s_es->s_mnt_count);
                }
            }
        }
    }
    if (!err)
        err = ext4_mark_iloc_dirty(handle, inode, &iloc);
    return err;
}

/*
 * ext4_dirty_inode() is called from __mark_inode_dirty()
 *
 * We're really interested in the case where a file is being extended.
 * i_size has been changed by generic_commit_write() and we thus need
 * to include the updated inode in the current transaction.
 *
 * Also, dquot_alloc_block() will always dirty the inode when blocks
 * are allocated to the file.
 *
 * If the inode is marked synchronous, we don't honour that here - doing
 * so would cause a commit on atime updates, which we don't bother doing.
 * We handle synchronous inodes at the highest possible level.
 */
void ext4_dirty_inode(struct inode *inode, int flags)
{
    handle_t *handle;

    handle = ext4_journal_start(inode, 2);
    if (IS_ERR(handle))
        goto out;

    ext4_mark_inode_dirty(handle, inode);

    ext4_journal_stop(handle);
out:
    return;
}

#if 0
/*
 * Bind an inode's backing buffer_head into this transaction, to prevent
 * it from being flushed to disk early.  Unlike
 * ext4_reserve_inode_write, this leaves behind no bh reference and
 * returns no iloc structure, so the caller needs to repeat the iloc
 * lookup to mark the inode dirty later.
 */
static int ext4_pin_inode(handle_t *handle, struct inode *inode)
{
    struct ext4_iloc iloc;

    int err = 0;
    if (handle) {
        err = ext4_get_inode_loc(inode, &iloc);
        if (!err) {
            BUFFER_TRACE(iloc.bh, "get_write_access");
            err = jbd2_journal_get_write_access(handle, iloc.bh);
            if (!err)
                err = ext4_handle_dirty_metadata(handle,
                                 NULL,
                                 iloc.bh);
            brelse(iloc.bh);
        }
    }
    ext4_std_error(inode->i_sb, err);
    return err;
}
#endif

int ext4_change_inode_journal_flag(struct inode *inode, int val)
{
    journal_t *journal;
    handle_t *handle;
    int err;

    /*
     * We have to be very careful here: changing a data block's
     * journaling status dynamically is dangerous.  If we write a
     * data block to the journal, change the status and then delete
     * that block, we risk forgetting to revoke the old log record
     * from the journal and so a subsequent replay can corrupt data.
     * So, first we make sure that the journal is empty and that
     * nobody is changing anything.
     */

    journal = EXT4_JOURNAL(inode);
    if (!journal)
        return 0;
    if (is_journal_aborted(journal))
        return -EROFS;
    /* We have to allocate physical blocks for delalloc blocks
     * before flushing journal. otherwise delalloc blocks can not
     * be allocated any more. even more truncate on delalloc blocks
     * could trigger BUG by flushing delalloc blocks in journal.
     * There is no delalloc block in non-journal data mode.
     */
    if (val && test_opt(inode->i_sb, DELALLOC)) {
        err = ext4_alloc_da_blocks(inode);
        if (err < 0)
            return err;
    }

    /* Wait for all existing dio workers */
    ext4_inode_block_unlocked_dio(inode);
    inode_dio_wait(inode);

    jbd2_journal_lock_updates(journal);

    /*
     * OK, there are no updates running now, and all cached data is
     * synced to disk.  We are now in a completely consistent state
     * which doesn't have anything in the journal, and we know that
     * no filesystem updates are running, so it is safe to modify
     * the inode's in-core data-journaling state flag now.
     */

    if (val)
        ext4_set_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
    else {
        jbd2_journal_flush(journal);
        ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
    }
    ext4_set_aops(inode);

    jbd2_journal_unlock_updates(journal);
    ext4_inode_resume_unlocked_dio(inode);

    /* Finally we can mark the inode as dirty. */

    handle = ext4_journal_start(inode, 1);
    if (IS_ERR(handle))
        return PTR_ERR(handle);

    err = ext4_mark_inode_dirty(handle, inode);
    ext4_handle_sync(handle);
    ext4_journal_stop(handle);
    ext4_std_error(inode->i_sb, err);

    return err;
}

static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
{
    return !buffer_mapped(bh);
}

int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
    struct page *page = vmf->page;
    loff_t size;
    unsigned long len;
    int ret;
    struct file *file = vma->vm_file;
    struct inode *inode = file->f_path.dentry->d_inode;
    struct address_space *mapping = inode->i_mapping;
    handle_t *handle;
    get_block_t *get_block;
    int retries = 0;

    sb_start_pagefault(inode->i_sb);
    file_update_time(vma->vm_file);
    /* Delalloc case is easy... */
    if (test_opt(inode->i_sb, DELALLOC) &&
        !ext4_should_journal_data(inode) &&
        !ext4_nonda_switch(inode->i_sb)) {
        do {
            ret = __block_page_mkwrite(vma, vmf,
                           ext4_da_get_block_prep);
        } while (ret == -ENOSPC &&
               ext4_should_retry_alloc(inode->i_sb, &retries));
        goto out_ret;
    }

    lock_page(page);
    size = i_size_read(inode);
    /* Page got truncated from under us? */
    if (page->mapping != mapping || page_offset(page) > size) {
        unlock_page(page);
        ret = VM_FAULT_NOPAGE;
        goto out;
    }

    if (page->index == size >> PAGE_CACHE_SHIFT)
        len = size & ~PAGE_CACHE_MASK;
    else
        len = PAGE_CACHE_SIZE;
    /*
     * Return if we have all the buffers mapped. This avoids the need to do
     * journal_start/journal_stop which can block and take a long time
     */
    if (page_has_buffers(page)) {
        if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
                    ext4_bh_unmapped)) {
            /* Wait so that we don't change page under IO */
            wait_on_page_writeback(page);
            ret = VM_FAULT_LOCKED;
            goto out;
        }
    }
    unlock_page(page);
    /* OK, we need to fill the hole... */
    if (ext4_should_dioread_nolock(inode))
        get_block = ext4_get_block_write;
    else
        get_block = ext4_get_block;
retry_alloc:
    handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
    if (IS_ERR(handle)) {
        ret = VM_FAULT_SIGBUS;
        goto out;
    }
    ret = __block_page_mkwrite(vma, vmf, get_block);
    if (!ret && ext4_should_journal_data(inode)) {
        if (walk_page_buffers(handle, page_buffers(page), 0,
              PAGE_CACHE_SIZE, NULL, do_journal_get_write_access)) {
            unlock_page(page);
            ret = VM_FAULT_SIGBUS;
            ext4_journal_stop(handle);
            goto out;
        }
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
    }
    ext4_journal_stop(handle);
    if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
        goto retry_alloc;
out_ret:
    ret = block_page_mkwrite_return(ret);
out:
    sb_end_pagefault(inode->i_sb);
    return ret;
}