file.c

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/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Authors: Artem Bityutskiy (Битюцкий Артём)
 *          Adrian Hunter
 */

/*
 * This file implements VFS file and inode operations for regular files, device
 * nodes and symlinks as well as address space operations.
 *
 * UBIFS uses 2 page flags: @PG_private and @PG_checked. @PG_private is set if
 * the page is dirty and is used for optimization purposes - dirty pages are
 * not budgeted so the flag shows that 'ubifs_write_end()' should not release
 * the budget for this page. The @PG_checked flag is set if full budgeting is
 * required for the page e.g., when it corresponds to a file hole or it is
 * beyond the file size. The budgeting is done in 'ubifs_write_begin()', because
 * it is OK to fail in this function, and the budget is released in
 * 'ubifs_write_end()'. So the @PG_private and @PG_checked flags carry
 * information about how the page was budgeted, to make it possible to release
 * the budget properly.
 *
 * A thing to keep in mind: inode @i_mutex is locked in most VFS operations we
 * implement. However, this is not true for 'ubifs_writepage()', which may be
 * called with @i_mutex unlocked. For example, when flusher thread is doing
 * background write-back, it calls 'ubifs_writepage()' with unlocked @i_mutex.
 * At "normal" work-paths the @i_mutex is locked in 'ubifs_writepage()', e.g.
 * in the "sys_write -> alloc_pages -> direct reclaim path". So, in
 * 'ubifs_writepage()' we are only guaranteed that the page is locked.
 *
 * Similarly, @i_mutex is not always locked in 'ubifs_readpage()', e.g., the
 * read-ahead path does not lock it ("sys_read -> generic_file_aio_read ->
 * ondemand_readahead -> readpage"). In case of readahead, @I_SYNC flag is not
 * set as well. However, UBIFS disables readahead.
 */

#include "ubifs.h"
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/slab.h>

static int read_block(struct inode *inode, void *addr, unsigned int block,
              struct ubifs_data_node *dn)
{
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    int err, len, out_len;
    union ubifs_key key;
    unsigned int dlen;

    data_key_init(c, &key, inode->i_ino, block);
    err = ubifs_tnc_lookup(c, &key, dn);
    if (err) {
        if (err == -ENOENT)
            /* Not found, so it must be a hole */
            memset(addr, 0, UBIFS_BLOCK_SIZE);
        return err;
    }

    ubifs_assert(le64_to_cpu(dn->ch.sqnum) >
             ubifs_inode(inode)->creat_sqnum);
    len = le32_to_cpu(dn->size);
    if (len <= 0 || len > UBIFS_BLOCK_SIZE)
        goto dump;

    dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;
    out_len = UBIFS_BLOCK_SIZE;
    err = ubifs_decompress(&dn->data, dlen, addr, &out_len,
                   le16_to_cpu(dn->compr_type));
    if (err || len != out_len)
        goto dump;

    /*
     * Data length can be less than a full block, even for blocks that are
     * not the last in the file (e.g., as a result of making a hole and
     * appending data). Ensure that the remainder is zeroed out.
     */
    if (len < UBIFS_BLOCK_SIZE)
        memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);

    return 0;

dump:
    ubifs_err("bad data node (block %u, inode %lu)",
          block, inode->i_ino);
    ubifs_dump_node(c, dn);
    return -EINVAL;
}

static int do_readpage(struct page *page)
{
    void *addr;
    int err = 0, i;
    unsigned int block, beyond;
    struct ubifs_data_node *dn;
    struct inode *inode = page->mapping->host;
    loff_t i_size = i_size_read(inode);

    dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
        inode->i_ino, page->index, i_size, page->flags);
    ubifs_assert(!PageChecked(page));
    ubifs_assert(!PagePrivate(page));

    addr = kmap(page);

    block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
    beyond = (i_size + UBIFS_BLOCK_SIZE - 1) >> UBIFS_BLOCK_SHIFT;
    if (block >= beyond) {
        /* Reading beyond inode */
        SetPageChecked(page);
        memset(addr, 0, PAGE_CACHE_SIZE);
        goto out;
    }

    dn = kmalloc(UBIFS_MAX_DATA_NODE_SZ, GFP_NOFS);
    if (!dn) {
        err = -ENOMEM;
        goto error;
    }

    i = 0;
    while (1) {
        int ret;

        if (block >= beyond) {
            /* Reading beyond inode */
            err = -ENOENT;
            memset(addr, 0, UBIFS_BLOCK_SIZE);
        } else {
            ret = read_block(inode, addr, block, dn);
            if (ret) {
                err = ret;
                if (err != -ENOENT)
                    break;
            } else if (block + 1 == beyond) {
                int dlen = le32_to_cpu(dn->size);
                int ilen = i_size & (UBIFS_BLOCK_SIZE - 1);

                if (ilen && ilen < dlen)
                    memset(addr + ilen, 0, dlen - ilen);
            }
        }
        if (++i >= UBIFS_BLOCKS_PER_PAGE)
            break;
        block += 1;
        addr += UBIFS_BLOCK_SIZE;
    }
    if (err) {
        if (err == -ENOENT) {
            /* Not found, so it must be a hole */
            SetPageChecked(page);
            dbg_gen("hole");
            goto out_free;
        }
        ubifs_err("cannot read page %lu of inode %lu, error %d",
              page->index, inode->i_ino, err);
        goto error;
    }

out_free:
    kfree(dn);
out:
    SetPageUptodate(page);
    ClearPageError(page);
    flush_dcache_page(page);
    kunmap(page);
    return 0;

error:
    kfree(dn);
    ClearPageUptodate(page);
    SetPageError(page);
    flush_dcache_page(page);
    kunmap(page);
    return err;
}

static void release_new_page_budget(struct ubifs_info *c)
{
    struct ubifs_budget_req req = { .recalculate = 1, .new_page = 1 };

    ubifs_release_budget(c, &req);
}

static void release_existing_page_budget(struct ubifs_info *c)
{
    struct ubifs_budget_req req = { .dd_growth = c->bi.page_budget};

    ubifs_release_budget(c, &req);
}

static int write_begin_slow(struct address_space *mapping,
                loff_t pos, unsigned len, struct page **pagep,
                unsigned flags)
{
    struct inode *inode = mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    pgoff_t index = pos >> PAGE_CACHE_SHIFT;
    struct ubifs_budget_req req = { .new_page = 1 };
    int uninitialized_var(err), appending = !!(pos + len > inode->i_size);
    struct page *page;

    dbg_gen("ino %lu, pos %llu, len %u, i_size %lld",
        inode->i_ino, pos, len, inode->i_size);

    /*
     * At the slow path we have to budget before locking the page, because
     * budgeting may force write-back, which would wait on locked pages and
     * deadlock if we had the page locked. At this point we do not know
     * anything about the page, so assume that this is a new page which is
     * written to a hole. This corresponds to largest budget. Later the
     * budget will be amended if this is not true.
     */
    if (appending)
        /* We are appending data, budget for inode change */
        req.dirtied_ino = 1;

    err = ubifs_budget_space(c, &req);
    if (unlikely(err))
        return err;

    page = grab_cache_page_write_begin(mapping, index, flags);
    if (unlikely(!page)) {
        ubifs_release_budget(c, &req);
        return -ENOMEM;
    }

    if (!PageUptodate(page)) {
        if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)
            SetPageChecked(page);
        else {
            err = do_readpage(page);
            if (err) {
                unlock_page(page);
                page_cache_release(page);
                return err;
            }
        }

        SetPageUptodate(page);
        ClearPageError(page);
    }

    if (PagePrivate(page))
        /*
         * The page is dirty, which means it was budgeted twice:
         *   o first time the budget was allocated by the task which
         *     made the page dirty and set the PG_private flag;
         *   o and then we budgeted for it for the second time at the
         *     very beginning of this function.
         *
         * So what we have to do is to release the page budget we
         * allocated.
         */
        release_new_page_budget(c);
    else if (!PageChecked(page))
        /*
         * We are changing a page which already exists on the media.
         * This means that changing the page does not make the amount
         * of indexing information larger, and this part of the budget
         * which we have already acquired may be released.
         */
        ubifs_convert_page_budget(c);

    if (appending) {
        struct ubifs_inode *ui = ubifs_inode(inode);

        /*
         * 'ubifs_write_end()' is optimized from the fast-path part of
         * 'ubifs_write_begin()' and expects the @ui_mutex to be locked
         * if data is appended.
         */
        mutex_lock(&ui->ui_mutex);
        if (ui->dirty)
            /*
             * The inode is dirty already, so we may free the
             * budget we allocated.
             */
            ubifs_release_dirty_inode_budget(c, ui);
    }

    *pagep = page;
    return 0;
}

static int allocate_budget(struct ubifs_info *c, struct page *page,
               struct ubifs_inode *ui, int appending)
{
    struct ubifs_budget_req req = { .fast = 1 };

    if (PagePrivate(page)) {
        if (!appending)
            /*
             * The page is dirty and we are not appending, which
             * means no budget is needed at all.
             */
            return 0;

        mutex_lock(&ui->ui_mutex);
        if (ui->dirty)
            /*
             * The page is dirty and we are appending, so the inode
             * has to be marked as dirty. However, it is already
             * dirty, so we do not need any budget. We may return,
             * but @ui->ui_mutex hast to be left locked because we
             * should prevent write-back from flushing the inode
             * and freeing the budget. The lock will be released in
             * 'ubifs_write_end()'.
             */
            return 0;

        /*
         * The page is dirty, we are appending, the inode is clean, so
         * we need to budget the inode change.
         */
        req.dirtied_ino = 1;
    } else {
        if (PageChecked(page))
            /*
             * The page corresponds to a hole and does not
             * exist on the media. So changing it makes
             * make the amount of indexing information
             * larger, and we have to budget for a new
             * page.
             */
            req.new_page = 1;
        else
            /*
             * Not a hole, the change will not add any new
             * indexing information, budget for page
             * change.
             */
            req.dirtied_page = 1;

        if (appending) {
            mutex_lock(&ui->ui_mutex);
            if (!ui->dirty)
                /*
                 * The inode is clean but we will have to mark
                 * it as dirty because we are appending. This
                 * needs a budget.
                 */
                req.dirtied_ino = 1;
        }
    }

    return ubifs_budget_space(c, &req);
}

/*
 * This function is called when a page of data is going to be written. Since
 * the page of data will not necessarily go to the flash straight away, UBIFS
 * has to reserve space on the media for it, which is done by means of
 * budgeting.
 *
 * This is the hot-path of the file-system and we are trying to optimize it as
 * much as possible. For this reasons it is split on 2 parts - slow and fast.
 *
 * There many budgeting cases:
 *     o a new page is appended - we have to budget for a new page and for
 *       changing the inode; however, if the inode is already dirty, there is
 *       no need to budget for it;
 *     o an existing clean page is changed - we have budget for it; if the page
 *       does not exist on the media (a hole), we have to budget for a new
 *       page; otherwise, we may budget for changing an existing page; the
 *       difference between these cases is that changing an existing page does
 *       not introduce anything new to the FS indexing information, so it does
 *       not grow, and smaller budget is acquired in this case;
 *     o an existing dirty page is changed - no need to budget at all, because
 *       the page budget has been acquired by earlier, when the page has been
 *       marked dirty.
 *
 * UBIFS budgeting sub-system may force write-back if it thinks there is no
 * space to reserve. This imposes some locking restrictions and makes it
 * impossible to take into account the above cases, and makes it impossible to
 * optimize budgeting.
 *
 * The solution for this is that the fast path of 'ubifs_write_begin()' assumes
 * there is a plenty of flash space and the budget will be acquired quickly,
 * without forcing write-back. The slow path does not make this assumption.
 */
static int ubifs_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;
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    struct ubifs_inode *ui = ubifs_inode(inode);
    pgoff_t index = pos >> PAGE_CACHE_SHIFT;
    int uninitialized_var(err), appending = !!(pos + len > inode->i_size);
    int skipped_read = 0;
    struct page *page;

    ubifs_assert(ubifs_inode(inode)->ui_size == inode->i_size);
    ubifs_assert(!c->ro_media && !c->ro_mount);

    if (unlikely(c->ro_error))
        return -EROFS;

    /* Try out the fast-path part first */
    page = grab_cache_page_write_begin(mapping, index, flags);
    if (unlikely(!page))
        return -ENOMEM;

    if (!PageUptodate(page)) {
        /* The page is not loaded from the flash */
        if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE) {
            /*
             * We change whole page so no need to load it. But we
             * do not know whether this page exists on the media or
             * not, so we assume the latter because it requires
             * larger budget. The assumption is that it is better
             * to budget a bit more than to read the page from the
             * media. Thus, we are setting the @PG_checked flag
             * here.
             */
            SetPageChecked(page);
            skipped_read = 1;
        } else {
            err = do_readpage(page);
            if (err) {
                unlock_page(page);
                page_cache_release(page);
                return err;
            }
        }

        SetPageUptodate(page);
        ClearPageError(page);
    }

    err = allocate_budget(c, page, ui, appending);
    if (unlikely(err)) {
        ubifs_assert(err == -ENOSPC);
        /*
         * If we skipped reading the page because we were going to
         * write all of it, then it is not up to date.
         */
        if (skipped_read) {
            ClearPageChecked(page);
            ClearPageUptodate(page);
        }
        /*
         * Budgeting failed which means it would have to force
         * write-back but didn't, because we set the @fast flag in the
         * request. Write-back cannot be done now, while we have the
         * page locked, because it would deadlock. Unlock and free
         * everything and fall-back to slow-path.
         */
        if (appending) {
            ubifs_assert(mutex_is_locked(&ui->ui_mutex));
            mutex_unlock(&ui->ui_mutex);
        }
        unlock_page(page);
        page_cache_release(page);

        return write_begin_slow(mapping, pos, len, pagep, flags);
    }

    /*
     * Whee, we acquired budgeting quickly - without involving
     * garbage-collection, committing or forcing write-back. We return
     * with @ui->ui_mutex locked if we are appending pages, and unlocked
     * otherwise. This is an optimization (slightly hacky though).
     */
    *pagep = page;
    return 0;

}

static void cancel_budget(struct ubifs_info *c, struct page *page,
              struct ubifs_inode *ui, int appending)
{
    if (appending) {
        if (!ui->dirty)
            ubifs_release_dirty_inode_budget(c, ui);
        mutex_unlock(&ui->ui_mutex);
    }
    if (!PagePrivate(page)) {
        if (PageChecked(page))
            release_new_page_budget(c);
        else
            release_existing_page_budget(c);
    }
}

static int ubifs_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;
    struct ubifs_inode *ui = ubifs_inode(inode);
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    loff_t end_pos = pos + len;
    int appending = !!(end_pos > inode->i_size);

    dbg_gen("ino %lu, pos %llu, pg %lu, len %u, copied %d, i_size %lld",
        inode->i_ino, pos, page->index, len, copied, inode->i_size);

    if (unlikely(copied < len && len == PAGE_CACHE_SIZE)) {
        /*
         * VFS copied less data to the page that it intended and
         * declared in its '->write_begin()' call via the @len
         * argument. If the page was not up-to-date, and @len was
         * @PAGE_CACHE_SIZE, the 'ubifs_write_begin()' function did
         * not load it from the media (for optimization reasons). This
         * means that part of the page contains garbage. So read the
         * page now.
         */
        dbg_gen("copied %d instead of %d, read page and repeat",
            copied, len);
        cancel_budget(c, page, ui, appending);
        ClearPageChecked(page);

        /*
         * Return 0 to force VFS to repeat the whole operation, or the
         * error code if 'do_readpage()' fails.
         */
        copied = do_readpage(page);
        goto out;
    }

    if (!PagePrivate(page)) {
        SetPagePrivate(page);
        atomic_long_inc(&c->dirty_pg_cnt);
        __set_page_dirty_nobuffers(page);
    }

    if (appending) {
        i_size_write(inode, end_pos);
        ui->ui_size = end_pos;
        /*
         * Note, we do not set @I_DIRTY_PAGES (which means that the
         * inode has dirty pages), this has been done in
         * '__set_page_dirty_nobuffers()'.
         */
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        ubifs_assert(mutex_is_locked(&ui->ui_mutex));
        mutex_unlock(&ui->ui_mutex);
    }

out:
    unlock_page(page);
    page_cache_release(page);
    return copied;
}

static int populate_page(struct ubifs_info *c, struct page *page,
             struct bu_info *bu, int *n)
{
    int i = 0, nn = *n, offs = bu->zbranch[0].offs, hole = 0, read = 0;
    struct inode *inode = page->mapping->host;
    loff_t i_size = i_size_read(inode);
    unsigned int page_block;
    void *addr, *zaddr;
    pgoff_t end_index;

    dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
        inode->i_ino, page->index, i_size, page->flags);

    addr = zaddr = kmap(page);

    end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;
    if (!i_size || page->index > end_index) {
        hole = 1;
        memset(addr, 0, PAGE_CACHE_SIZE);
        goto out_hole;
    }

    page_block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
    while (1) {
        int err, len, out_len, dlen;

        if (nn >= bu->cnt) {
            hole = 1;
            memset(addr, 0, UBIFS_BLOCK_SIZE);
        } else if (key_block(c, &bu->zbranch[nn].key) == page_block) {
            struct ubifs_data_node *dn;

            dn = bu->buf + (bu->zbranch[nn].offs - offs);

            ubifs_assert(le64_to_cpu(dn->ch.sqnum) >
                     ubifs_inode(inode)->creat_sqnum);

            len = le32_to_cpu(dn->size);
            if (len <= 0 || len > UBIFS_BLOCK_SIZE)
                goto out_err;

            dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;
            out_len = UBIFS_BLOCK_SIZE;
            err = ubifs_decompress(&dn->data, dlen, addr, &out_len,
                           le16_to_cpu(dn->compr_type));
            if (err || len != out_len)
                goto out_err;

            if (len < UBIFS_BLOCK_SIZE)
                memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);

            nn += 1;
            read = (i << UBIFS_BLOCK_SHIFT) + len;
        } else if (key_block(c, &bu->zbranch[nn].key) < page_block) {
            nn += 1;
            continue;
        } else {
            hole = 1;
            memset(addr, 0, UBIFS_BLOCK_SIZE);
        }
        if (++i >= UBIFS_BLOCKS_PER_PAGE)
            break;
        addr += UBIFS_BLOCK_SIZE;
        page_block += 1;
    }

    if (end_index == page->index) {
        int len = i_size & (PAGE_CACHE_SIZE - 1);

        if (len && len < read)
            memset(zaddr + len, 0, read - len);
    }

out_hole:
    if (hole) {
        SetPageChecked(page);
        dbg_gen("hole");
    }

    SetPageUptodate(page);
    ClearPageError(page);
    flush_dcache_page(page);
    kunmap(page);
    *n = nn;
    return 0;

out_err:
    ClearPageUptodate(page);
    SetPageError(page);
    flush_dcache_page(page);
    kunmap(page);
    ubifs_err("bad data node (block %u, inode %lu)",
          page_block, inode->i_ino);
    return -EINVAL;
}

static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
                  struct page *page1)
{
    pgoff_t offset = page1->index, end_index;
    struct address_space *mapping = page1->mapping;
    struct inode *inode = mapping->host;
    struct ubifs_inode *ui = ubifs_inode(inode);
    int err, page_idx, page_cnt, ret = 0, n = 0;
    int allocate = bu->buf ? 0 : 1;
    loff_t isize;

    err = ubifs_tnc_get_bu_keys(c, bu);
    if (err)
        goto out_warn;

    if (bu->eof) {
        /* Turn off bulk-read at the end of the file */
        ui->read_in_a_row = 1;
        ui->bulk_read = 0;
    }

    page_cnt = bu->blk_cnt >> UBIFS_BLOCKS_PER_PAGE_SHIFT;
    if (!page_cnt) {
        /*
         * This happens when there are multiple blocks per page and the
         * blocks for the first page we are looking for, are not
         * together. If all the pages were like this, bulk-read would
         * reduce performance, so we turn it off for a while.
         */
        goto out_bu_off;
    }

    if (bu->cnt) {
        if (allocate) {
            /*
             * Allocate bulk-read buffer depending on how many data
             * nodes we are going to read.
             */
            bu->buf_len = bu->zbranch[bu->cnt - 1].offs +
                      bu->zbranch[bu->cnt - 1].len -
                      bu->zbranch[0].offs;
            ubifs_assert(bu->buf_len > 0);
            ubifs_assert(bu->buf_len <= c->leb_size);
            bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
            if (!bu->buf)
                goto out_bu_off;
        }

        err = ubifs_tnc_bulk_read(c, bu);
        if (err)
            goto out_warn;
    }

    err = populate_page(c, page1, bu, &n);
    if (err)
        goto out_warn;

    unlock_page(page1);
    ret = 1;

    isize = i_size_read(inode);
    if (isize == 0)
        goto out_free;
    end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);

    for (page_idx = 1; page_idx < page_cnt; page_idx++) {
        pgoff_t page_offset = offset + page_idx;
        struct page *page;

        if (page_offset > end_index)
            break;
        page = find_or_create_page(mapping, page_offset,
                       GFP_NOFS | __GFP_COLD);
        if (!page)
            break;
        if (!PageUptodate(page))
            err = populate_page(c, page, bu, &n);
        unlock_page(page);
        page_cache_release(page);
        if (err)
            break;
    }

    ui->last_page_read = offset + page_idx - 1;

out_free:
    if (allocate)
        kfree(bu->buf);
    return ret;

out_warn:
    ubifs_warn("ignoring error %d and skipping bulk-read", err);
    goto out_free;

out_bu_off:
    ui->read_in_a_row = ui->bulk_read = 0;
    goto out_free;
}

static int ubifs_bulk_read(struct page *page)
{
    struct inode *inode = page->mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    struct ubifs_inode *ui = ubifs_inode(inode);
    pgoff_t index = page->index, last_page_read = ui->last_page_read;
    struct bu_info *bu;
    int err = 0, allocated = 0;

    ui->last_page_read = index;
    if (!c->bulk_read)
        return 0;

    /*
     * Bulk-read is protected by @ui->ui_mutex, but it is an optimization,
     * so don't bother if we cannot lock the mutex.
     */
    if (!mutex_trylock(&ui->ui_mutex))
        return 0;

    if (index != last_page_read + 1) {
        /* Turn off bulk-read if we stop reading sequentially */
        ui->read_in_a_row = 1;
        if (ui->bulk_read)
            ui->bulk_read = 0;
        goto out_unlock;
    }

    if (!ui->bulk_read) {
        ui->read_in_a_row += 1;
        if (ui->read_in_a_row < 3)
            goto out_unlock;
        /* Three reads in a row, so switch on bulk-read */
        ui->bulk_read = 1;
    }

    /*
     * If possible, try to use pre-allocated bulk-read information, which
     * is protected by @c->bu_mutex.
     */
    if (mutex_trylock(&c->bu_mutex))
        bu = &c->bu;
    else {
        bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
        if (!bu)
            goto out_unlock;

        bu->buf = NULL;
        allocated = 1;
    }

    bu->buf_len = c->max_bu_buf_len;
    data_key_init(c, &bu->key, inode->i_ino,
              page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT);
    err = ubifs_do_bulk_read(c, bu, page);

    if (!allocated)
        mutex_unlock(&c->bu_mutex);
    else
        kfree(bu);

out_unlock:
    mutex_unlock(&ui->ui_mutex);
    return err;
}

static int ubifs_readpage(struct file *file, struct page *page)
{
    if (ubifs_bulk_read(page))
        return 0;
    do_readpage(page);
    unlock_page(page);
    return 0;
}

static int do_writepage(struct page *page, int len)
{
    int err = 0, i, blen;
    unsigned int block;
    void *addr;
    union ubifs_key key;
    struct inode *inode = page->mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;

#ifdef UBIFS_DEBUG
    spin_lock(&ui->ui_lock);
    ubifs_assert(page->index <= ui->synced_i_size << PAGE_CACHE_SIZE);
    spin_unlock(&ui->ui_lock);
#endif

    /* Update radix tree tags */
    set_page_writeback(page);

    addr = kmap(page);
    block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
    i = 0;
    while (len) {
        blen = min_t(int, len, UBIFS_BLOCK_SIZE);
        data_key_init(c, &key, inode->i_ino, block);
        err = ubifs_jnl_write_data(c, inode, &key, addr, blen);
        if (err)
            break;
        if (++i >= UBIFS_BLOCKS_PER_PAGE)
            break;
        block += 1;
        addr += blen;
        len -= blen;
    }
    if (err) {
        SetPageError(page);
        ubifs_err("cannot write page %lu of inode %lu, error %d",
              page->index, inode->i_ino, err);
        ubifs_ro_mode(c, err);
    }

    ubifs_assert(PagePrivate(page));
    if (PageChecked(page))
        release_new_page_budget(c);
    else
        release_existing_page_budget(c);

    atomic_long_dec(&c->dirty_pg_cnt);
    ClearPagePrivate(page);
    ClearPageChecked(page);

    kunmap(page);
    unlock_page(page);
    end_page_writeback(page);
    return err;
}

/*
 * When writing-back dirty inodes, VFS first writes-back pages belonging to the
 * inode, then the inode itself. For UBIFS this may cause a problem. Consider a
 * situation when a we have an inode with size 0, then a megabyte of data is
 * appended to the inode, then write-back starts and flushes some amount of the
 * dirty pages, the journal becomes full, commit happens and finishes, and then
 * an unclean reboot happens. When the file system is mounted next time, the
 * inode size would still be 0, but there would be many pages which are beyond
 * the inode size, they would be indexed and consume flash space. Because the
 * journal has been committed, the replay would not be able to detect this
 * situation and correct the inode size. This means UBIFS would have to scan
 * whole index and correct all inode sizes, which is long an unacceptable.
 *
 * To prevent situations like this, UBIFS writes pages back only if they are
 * within the last synchronized inode size, i.e. the size which has been
 * written to the flash media last time. Otherwise, UBIFS forces inode
 * write-back, thus making sure the on-flash inode contains current inode size,
 * and then keeps writing pages back.
 *
 * Some locking issues explanation. 'ubifs_writepage()' first is called with
 * the page locked, and it locks @ui_mutex. However, write-back does take inode
 * @i_mutex, which means other VFS operations may be run on this inode at the
 * same time. And the problematic one is truncation to smaller size, from where
 * we have to call 'truncate_setsize()', which first changes @inode->i_size,
 * then drops the truncated pages. And while dropping the pages, it takes the
 * page lock. This means that 'do_truncation()' cannot call 'truncate_setsize()'
 * with @ui_mutex locked, because it would deadlock with 'ubifs_writepage()'.
 * This means that @inode->i_size is changed while @ui_mutex is unlocked.
 *
 * XXX(truncate): with the new truncate sequence this is not true anymore,
 * and the calls to truncate_setsize can be move around freely.  They should
 * be moved to the very end of the truncate sequence.
 *
 * But in 'ubifs_writepage()' we have to guarantee that we do not write beyond
 * inode size. How do we do this if @inode->i_size may became smaller while we
 * are in the middle of 'ubifs_writepage()'? The UBIFS solution is the
 * @ui->ui_isize "shadow" field which UBIFS uses instead of @inode->i_size
 * internally and updates it under @ui_mutex.
 *
 * Q: why we do not worry that if we race with truncation, we may end up with a
 * situation when the inode is truncated while we are in the middle of
 * 'do_writepage()', so we do write beyond inode size?
 * A: If we are in the middle of 'do_writepage()', truncation would be locked
 * on the page lock and it would not write the truncated inode node to the
 * journal before we have finished.
 */
static int ubifs_writepage(struct page *page, struct writeback_control *wbc)
{
    struct inode *inode = page->mapping->host;
    struct ubifs_inode *ui = ubifs_inode(inode);
    loff_t i_size =  i_size_read(inode), synced_i_size;
    pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
    int err, len = i_size & (PAGE_CACHE_SIZE - 1);
    void *kaddr;

    dbg_gen("ino %lu, pg %lu, pg flags %#lx",
        inode->i_ino, page->index, page->flags);
    ubifs_assert(PagePrivate(page));

    /* Is the page fully outside @i_size? (truncate in progress) */
    if (page->index > end_index || (page->index == end_index && !len)) {
        err = 0;
        goto out_unlock;
    }

    spin_lock(&ui->ui_lock);
    synced_i_size = ui->synced_i_size;
    spin_unlock(&ui->ui_lock);

    /* Is the page fully inside @i_size? */
    if (page->index < end_index) {
        if (page->index >= synced_i_size >> PAGE_CACHE_SHIFT) {
            err = inode->i_sb->s_op->write_inode(inode, NULL);
            if (err)
                goto out_unlock;
            /*
             * The inode has been written, but the write-buffer has
             * not been synchronized, so in case of an unclean
             * reboot we may end up with some pages beyond inode
             * size, but they would be in the journal (because
             * commit flushes write buffers) and recovery would deal
             * with this.
             */
        }
        return do_writepage(page, PAGE_CACHE_SIZE);
    }

    /*
     * The page straddles @i_size. It must be zeroed out on each and every
     * writepage invocation because it may be mmapped. "A file is mapped
     * in multiples of the page size. For a file that is not a multiple of
     * the page size, the remaining memory is zeroed when mapped, and
     * writes to that region are not written out to the file."
     */
    kaddr = kmap_atomic(page);
    memset(kaddr + len, 0, PAGE_CACHE_SIZE - len);
    flush_dcache_page(page);
    kunmap_atomic(kaddr);

    if (i_size > synced_i_size) {
        err = inode->i_sb->s_op->write_inode(inode, NULL);
        if (err)
            goto out_unlock;
    }

    return do_writepage(page, len);

out_unlock:
    unlock_page(page);
    return err;
}

static void do_attr_changes(struct inode *inode, const struct iattr *attr)
{
    if (attr->ia_valid & ATTR_UID)
        inode->i_uid = attr->ia_uid;
    if (attr->ia_valid & ATTR_GID)
        inode->i_gid = attr->ia_gid;
    if (attr->ia_valid & ATTR_ATIME)
        inode->i_atime = timespec_trunc(attr->ia_atime,
                        inode->i_sb->s_time_gran);
    if (attr->ia_valid & ATTR_MTIME)
        inode->i_mtime = timespec_trunc(attr->ia_mtime,
                        inode->i_sb->s_time_gran);
    if (attr->ia_valid & ATTR_CTIME)
        inode->i_ctime = timespec_trunc(attr->ia_ctime,
                        inode->i_sb->s_time_gran);
    if (attr->ia_valid & ATTR_MODE) {
        umode_t mode = attr->ia_mode;

        if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
            mode &= ~S_ISGID;
        inode->i_mode = mode;
    }
}

static int do_truncation(struct ubifs_info *c, struct inode *inode,
             const struct iattr *attr)
{
    int err;
    struct ubifs_budget_req req;
    loff_t old_size = inode->i_size, new_size = attr->ia_size;
    int offset = new_size & (UBIFS_BLOCK_SIZE - 1), budgeted = 1;
    struct ubifs_inode *ui = ubifs_inode(inode);

    dbg_gen("ino %lu, size %lld -> %lld", inode->i_ino, old_size, new_size);
    memset(&req, 0, sizeof(struct ubifs_budget_req));

    /*
     * If this is truncation to a smaller size, and we do not truncate on a
     * block boundary, budget for changing one data block, because the last
     * block will be re-written.
     */
    if (new_size & (UBIFS_BLOCK_SIZE - 1))
        req.dirtied_page = 1;

    req.dirtied_ino = 1;
    /* A funny way to budget for truncation node */
    req.dirtied_ino_d = UBIFS_TRUN_NODE_SZ;
    err = ubifs_budget_space(c, &req);
    if (err) {
        /*
         * Treat truncations to zero as deletion and always allow them,
         * just like we do for '->unlink()'.
         */
        if (new_size || err != -ENOSPC)
            return err;
        budgeted = 0;
    }

    truncate_setsize(inode, new_size);

    if (offset) {
        pgoff_t index = new_size >> PAGE_CACHE_SHIFT;
        struct page *page;

        page = find_lock_page(inode->i_mapping, index);
        if (page) {
            if (PageDirty(page)) {
                /*
                 * 'ubifs_jnl_truncate()' will try to truncate
                 * the last data node, but it contains
                 * out-of-date data because the page is dirty.
                 * Write the page now, so that
                 * 'ubifs_jnl_truncate()' will see an already
                 * truncated (and up to date) data node.
                 */
                ubifs_assert(PagePrivate(page));

                clear_page_dirty_for_io(page);
                if (UBIFS_BLOCKS_PER_PAGE_SHIFT)
                    offset = new_size &
                         (PAGE_CACHE_SIZE - 1);
                err = do_writepage(page, offset);
                page_cache_release(page);
                if (err)
                    goto out_budg;
                /*
                 * We could now tell 'ubifs_jnl_truncate()' not
                 * to read the last block.
                 */
            } else {
                /*
                 * We could 'kmap()' the page and pass the data
                 * to 'ubifs_jnl_truncate()' to save it from
                 * having to read it.
                 */
                unlock_page(page);
                page_cache_release(page);
            }
        }
    }

    mutex_lock(&ui->ui_mutex);
    ui->ui_size = inode->i_size;
    /* Truncation changes inode [mc]time */
    inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
    /* Other attributes may be changed at the same time as well */
    do_attr_changes(inode, attr);
    err = ubifs_jnl_truncate(c, inode, old_size, new_size);
    mutex_unlock(&ui->ui_mutex);

out_budg:
    if (budgeted)
        ubifs_release_budget(c, &req);
    else {
        c->bi.nospace = c->bi.nospace_rp = 0;
        smp_wmb();
    }
    return err;
}

static int do_setattr(struct ubifs_info *c, struct inode *inode,
              const struct iattr *attr)
{
    int err, release;
    loff_t new_size = attr->ia_size;
    struct ubifs_inode *ui = ubifs_inode(inode);
    struct ubifs_budget_req req = { .dirtied_ino = 1,
                .dirtied_ino_d = ALIGN(ui->data_len, 8) };

    err = ubifs_budget_space(c, &req);
    if (err)
        return err;

    if (attr->ia_valid & ATTR_SIZE) {
        dbg_gen("size %lld -> %lld", inode->i_size, new_size);
        truncate_setsize(inode, new_size);
    }

    mutex_lock(&ui->ui_mutex);
    if (attr->ia_valid & ATTR_SIZE) {
        /* Truncation changes inode [mc]time */
        inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
        /* 'truncate_setsize()' changed @i_size, update @ui_size */
        ui->ui_size = inode->i_size;
    }

    do_attr_changes(inode, attr);

    release = ui->dirty;
    if (attr->ia_valid & ATTR_SIZE)
        /*
         * Inode length changed, so we have to make sure
         * @I_DIRTY_DATASYNC is set.
         */
         __mark_inode_dirty(inode, I_DIRTY_SYNC | I_DIRTY_DATASYNC);
    else
        mark_inode_dirty_sync(inode);
    mutex_unlock(&ui->ui_mutex);

    if (release)
        ubifs_release_budget(c, &req);
    if (IS_SYNC(inode))
        err = inode->i_sb->s_op->write_inode(inode, NULL);
    return err;
}

int ubifs_setattr(struct dentry *dentry, struct iattr *attr)
{
    int err;
    struct inode *inode = dentry->d_inode;
    struct ubifs_info *c = inode->i_sb->s_fs_info;

    dbg_gen("ino %lu, mode %#x, ia_valid %#x",
        inode->i_ino, inode->i_mode, attr->ia_valid);
    err = inode_change_ok(inode, attr);
    if (err)
        return err;

    err = dbg_check_synced_i_size(c, inode);
    if (err)
        return err;

    if ((attr->ia_valid & ATTR_SIZE) && attr->ia_size < inode->i_size)
        /* Truncation to a smaller size */
        err = do_truncation(c, inode, attr);
    else
        err = do_setattr(c, inode, attr);

    return err;
}

static void ubifs_invalidatepage(struct page *page, unsigned long offset)
{
    struct inode *inode = page->mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;

    ubifs_assert(PagePrivate(page));
    if (offset)
        /* Partial page remains dirty */
        return;

    if (PageChecked(page))
        release_new_page_budget(c);
    else
        release_existing_page_budget(c);

    atomic_long_dec(&c->dirty_pg_cnt);
    ClearPagePrivate(page);
    ClearPageChecked(page);
}

static void *ubifs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
    struct ubifs_inode *ui = ubifs_inode(dentry->d_inode);

    nd_set_link(nd, ui->data);
    return NULL;
}

int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
    struct inode *inode = file->f_mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    int err;

    dbg_gen("syncing inode %lu", inode->i_ino);

    if (c->ro_mount)
        /*
         * For some really strange reasons VFS does not filter out
         * 'fsync()' for R/O mounted file-systems as per 2.6.39.
         */
        return 0;

    err = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (err)
        return err;
    mutex_lock(&inode->i_mutex);

    /* Synchronize the inode unless this is a 'datasync()' call. */
    if (!datasync || (inode->i_state & I_DIRTY_DATASYNC)) {
        err = inode->i_sb->s_op->write_inode(inode, NULL);
        if (err)
            goto out;
    }

    /*
     * Nodes related to this inode may still sit in a write-buffer. Flush
     * them.
     */
    err = ubifs_sync_wbufs_by_inode(c, inode);
out:
    mutex_unlock(&inode->i_mutex);
    return err;
}

static inline int mctime_update_needed(const struct inode *inode,
                       const struct timespec *now)
{
    if (!timespec_equal(&inode->i_mtime, now) ||
        !timespec_equal(&inode->i_ctime, now))
        return 1;
    return 0;
}

static int update_mctime(struct ubifs_info *c, struct inode *inode)
{
    struct timespec now = ubifs_current_time(inode);
    struct ubifs_inode *ui = ubifs_inode(inode);

    if (mctime_update_needed(inode, &now)) {
        int err, release;
        struct ubifs_budget_req req = { .dirtied_ino = 1,
                .dirtied_ino_d = ALIGN(ui->data_len, 8) };

        err = ubifs_budget_space(c, &req);
        if (err)
            return err;

        mutex_lock(&ui->ui_mutex);
        inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
        release = ui->dirty;
        mark_inode_dirty_sync(inode);
        mutex_unlock(&ui->ui_mutex);
        if (release)
            ubifs_release_budget(c, &req);
    }

    return 0;
}

static ssize_t ubifs_aio_write(struct kiocb *iocb, const struct iovec *iov,
                   unsigned long nr_segs, loff_t pos)
{
    int err;
    struct inode *inode = iocb->ki_filp->f_mapping->host;
    struct ubifs_info *c = inode->i_sb->s_fs_info;

    err = update_mctime(c, inode);
    if (err)
        return err;

    return generic_file_aio_write(iocb, iov, nr_segs, pos);
}

static int ubifs_set_page_dirty(struct page *page)
{
    int ret;

    ret = __set_page_dirty_nobuffers(page);
    /*
     * An attempt to dirty a page without budgeting for it - should not
     * happen.
     */
    ubifs_assert(ret == 0);
    return ret;
}

static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags)
{
    /*
     * An attempt to release a dirty page without budgeting for it - should
     * not happen.
     */
    if (PageWriteback(page))
        return 0;
    ubifs_assert(PagePrivate(page));
    ubifs_assert(0);
    ClearPagePrivate(page);
    ClearPageChecked(page);
    return 1;
}

/*
 * mmap()d file has taken write protection fault and is being made writable.
 * UBIFS must ensure page is budgeted for.
 */
static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma,
                 struct vm_fault *vmf)
{
    struct page *page = vmf->page;
    struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
    struct ubifs_info *c = inode->i_sb->s_fs_info;
    struct timespec now = ubifs_current_time(inode);
    struct ubifs_budget_req req = { .new_page = 1 };
    int err, update_time;

    dbg_gen("ino %lu, pg %lu, i_size %lld", inode->i_ino, page->index,
        i_size_read(inode));
    ubifs_assert(!c->ro_media && !c->ro_mount);

    if (unlikely(c->ro_error))
        return VM_FAULT_SIGBUS; /* -EROFS */

    /*
     * We have not locked @page so far so we may budget for changing the
     * page. Note, we cannot do this after we locked the page, because
     * budgeting may cause write-back which would cause deadlock.
     *
     * At the moment we do not know whether the page is dirty or not, so we
     * assume that it is not and budget for a new page. We could look at
     * the @PG_private flag and figure this out, but we may race with write
     * back and the page state may change by the time we lock it, so this
     * would need additional care. We do not bother with this at the
     * moment, although it might be good idea to do. Instead, we allocate
     * budget for a new page and amend it later on if the page was in fact
     * dirty.
     *
     * The budgeting-related logic of this function is similar to what we
     * do in 'ubifs_write_begin()' and 'ubifs_write_end()'. Glance there
     * for more comments.
     */
    update_time = mctime_update_needed(inode, &now);
    if (update_time)
        /*
         * We have to change inode time stamp which requires extra
         * budgeting.
         */
        req.dirtied_ino = 1;

    err = ubifs_budget_space(c, &req);
    if (unlikely(err)) {
        if (err == -ENOSPC)
            ubifs_warn("out of space for mmapped file (inode number %lu)",
                   inode->i_ino);
        return VM_FAULT_SIGBUS;
    }

    lock_page(page);
    if (unlikely(page->mapping != inode->i_mapping ||
             page_offset(page) > i_size_read(inode))) {
        /* Page got truncated out from underneath us */
        err = -EINVAL;
        goto out_unlock;
    }

    if (PagePrivate(page))
        release_new_page_budget(c);
    else {
        if (!PageChecked(page))
            ubifs_convert_page_budget(c);
        SetPagePrivate(page);
        atomic_long_inc(&c->dirty_pg_cnt);
        __set_page_dirty_nobuffers(page);
    }

    if (update_time) {
        int release;
        struct ubifs_inode *ui = ubifs_inode(inode);

        mutex_lock(&ui->ui_mutex);
        inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
        release = ui->dirty;
        mark_inode_dirty_sync(inode);
        mutex_unlock(&ui->ui_mutex);
        if (release)
            ubifs_release_dirty_inode_budget(c, ui);
    }

    unlock_page(page);
    return 0;

out_unlock:
    unlock_page(page);
    ubifs_release_budget(c, &req);
    if (err)
        err = VM_FAULT_SIGBUS;
    return err;
}

static const struct vm_operations_struct ubifs_file_vm_ops = {
    .fault        = filemap_fault,
    .page_mkwrite = ubifs_vm_page_mkwrite,
    .remap_pages = generic_file_remap_pages,
};

static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
    int err;

    err = generic_file_mmap(file, vma);
    if (err)
        return err;
    vma->vm_ops = &ubifs_file_vm_ops;
    return 0;
}

const struct address_space_operations ubifs_file_address_operations = {
    .readpage       = ubifs_readpage,
    .writepage      = ubifs_writepage,
    .write_begin    = ubifs_write_begin,
    .write_end      = ubifs_write_end,
    .invalidatepage = ubifs_invalidatepage,
    .set_page_dirty = ubifs_set_page_dirty,
    .releasepage    = ubifs_releasepage,
};

const struct inode_operations ubifs_file_inode_operations = {
    .setattr     = ubifs_setattr,
    .getattr     = ubifs_getattr,
    .setxattr    = ubifs_setxattr,
    .getxattr    = ubifs_getxattr,
    .listxattr   = ubifs_listxattr,
    .removexattr = ubifs_removexattr,
};

const struct inode_operations ubifs_symlink_inode_operations = {
    .readlink    = generic_readlink,
    .follow_link = ubifs_follow_link,
    .setattr     = ubifs_setattr,
    .getattr     = ubifs_getattr,
};

const struct file_operations ubifs_file_operations = {
    .llseek         = generic_file_llseek,
    .read           = do_sync_read,
    .write          = do_sync_write,
    .aio_read       = generic_file_aio_read,
    .aio_write      = ubifs_aio_write,
    .mmap           = ubifs_file_mmap,
    .fsync          = ubifs_fsync,
    .unlocked_ioctl = ubifs_ioctl,
    .splice_read    = generic_file_splice_read,
    .splice_write   = generic_file_splice_write,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = ubifs_compat_ioctl,
#endif
};