journal.c

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/*
 * linux/fs/jbd/journal.c
 *
 * Written by Stephen C. Tweedie <[email protected]>, 1998
 *
 * Copyright 1998 Red Hat corp --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Generic filesystem journal-writing code; part of the ext2fs
 * journaling system.
 *
 * This file manages journals: areas of disk reserved for logging
 * transactional updates.  This includes the kernel journaling thread
 * which is responsible for scheduling updates to the log.
 *
 * We do not actually manage the physical storage of the journal in this
 * file: that is left to a per-journal policy function, which allows us
 * to store the journal within a filesystem-specified area for ext2
 * journaling (ext2 can use a reserved inode for storing the log).
 */

#include <linux/module.h>
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/freezer.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/poison.h>
#include <linux/proc_fs.h>
#include <linux/debugfs.h>
#include <linux/ratelimit.h>

#define CREATE_TRACE_POINTS
#include <trace/events/jbd.h>

#include <asm/uaccess.h>
#include <asm/page.h>

EXPORT_SYMBOL(journal_start);
EXPORT_SYMBOL(journal_restart);
EXPORT_SYMBOL(journal_extend);
EXPORT_SYMBOL(journal_stop);
EXPORT_SYMBOL(journal_lock_updates);
EXPORT_SYMBOL(journal_unlock_updates);
EXPORT_SYMBOL(journal_get_write_access);
EXPORT_SYMBOL(journal_get_create_access);
EXPORT_SYMBOL(journal_get_undo_access);
EXPORT_SYMBOL(journal_dirty_data);
EXPORT_SYMBOL(journal_dirty_metadata);
EXPORT_SYMBOL(journal_release_buffer);
EXPORT_SYMBOL(journal_forget);
#if 0
EXPORT_SYMBOL(journal_sync_buffer);
#endif
EXPORT_SYMBOL(journal_flush);
EXPORT_SYMBOL(journal_revoke);

EXPORT_SYMBOL(journal_init_dev);
EXPORT_SYMBOL(journal_init_inode);
EXPORT_SYMBOL(journal_update_format);
EXPORT_SYMBOL(journal_check_used_features);
EXPORT_SYMBOL(journal_check_available_features);
EXPORT_SYMBOL(journal_set_features);
EXPORT_SYMBOL(journal_create);
EXPORT_SYMBOL(journal_load);
EXPORT_SYMBOL(journal_destroy);
EXPORT_SYMBOL(journal_abort);
EXPORT_SYMBOL(journal_errno);
EXPORT_SYMBOL(journal_ack_err);
EXPORT_SYMBOL(journal_clear_err);
EXPORT_SYMBOL(log_wait_commit);
EXPORT_SYMBOL(log_start_commit);
EXPORT_SYMBOL(journal_start_commit);
EXPORT_SYMBOL(journal_force_commit_nested);
EXPORT_SYMBOL(journal_wipe);
EXPORT_SYMBOL(journal_blocks_per_page);
EXPORT_SYMBOL(journal_invalidatepage);
EXPORT_SYMBOL(journal_try_to_free_buffers);
EXPORT_SYMBOL(journal_force_commit);

static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
static void __journal_abort_soft (journal_t *journal, int errno);
static const char *journal_dev_name(journal_t *journal, char *buffer);

/*
 * Helper function used to manage commit timeouts
 */

static void commit_timeout(unsigned long __data)
{
    struct task_struct * p = (struct task_struct *) __data;

    wake_up_process(p);
}

/*
 * kjournald: The main thread function used to manage a logging device
 * journal.
 *
 * This kernel thread is responsible for two things:
 *
 * 1) COMMIT:  Every so often we need to commit the current state of the
 *    filesystem to disk.  The journal thread is responsible for writing
 *    all of the metadata buffers to disk.
 *
 * 2) CHECKPOINT: We cannot reuse a used section of the log file until all
 *    of the data in that part of the log has been rewritten elsewhere on
 *    the disk.  Flushing these old buffers to reclaim space in the log is
 *    known as checkpointing, and this thread is responsible for that job.
 */

static int kjournald(void *arg)
{
    journal_t *journal = arg;
    transaction_t *transaction;

    /*
     * Set up an interval timer which can be used to trigger a commit wakeup
     * after the commit interval expires
     */
    setup_timer(&journal->j_commit_timer, commit_timeout,
            (unsigned long)current);

    set_freezable();

    /* Record that the journal thread is running */
    journal->j_task = current;
    wake_up(&journal->j_wait_done_commit);

    printk(KERN_INFO "kjournald starting.  Commit interval %ld seconds\n",
            journal->j_commit_interval / HZ);

    /*
     * And now, wait forever for commit wakeup events.
     */
    spin_lock(&journal->j_state_lock);

loop:
    if (journal->j_flags & JFS_UNMOUNT)
        goto end_loop;

    jbd_debug(1, "commit_sequence=%d, commit_request=%d\n",
        journal->j_commit_sequence, journal->j_commit_request);

    if (journal->j_commit_sequence != journal->j_commit_request) {
        jbd_debug(1, "OK, requests differ\n");
        spin_unlock(&journal->j_state_lock);
        del_timer_sync(&journal->j_commit_timer);
        journal_commit_transaction(journal);
        spin_lock(&journal->j_state_lock);
        goto loop;
    }

    wake_up(&journal->j_wait_done_commit);
    if (freezing(current)) {
        /*
         * The simpler the better. Flushing journal isn't a
         * good idea, because that depends on threads that may
         * be already stopped.
         */
        jbd_debug(1, "Now suspending kjournald\n");
        spin_unlock(&journal->j_state_lock);
        try_to_freeze();
        spin_lock(&journal->j_state_lock);
    } else {
        /*
         * We assume on resume that commits are already there,
         * so we don't sleep
         */
        DEFINE_WAIT(wait);
        int should_sleep = 1;

        prepare_to_wait(&journal->j_wait_commit, &wait,
                TASK_INTERRUPTIBLE);
        if (journal->j_commit_sequence != journal->j_commit_request)
            should_sleep = 0;
        transaction = journal->j_running_transaction;
        if (transaction && time_after_eq(jiffies,
                        transaction->t_expires))
            should_sleep = 0;
        if (journal->j_flags & JFS_UNMOUNT)
            should_sleep = 0;
        if (should_sleep) {
            spin_unlock(&journal->j_state_lock);
            schedule();
            spin_lock(&journal->j_state_lock);
        }
        finish_wait(&journal->j_wait_commit, &wait);
    }

    jbd_debug(1, "kjournald wakes\n");

    /*
     * Were we woken up by a commit wakeup event?
     */
    transaction = journal->j_running_transaction;
    if (transaction && time_after_eq(jiffies, transaction->t_expires)) {
        journal->j_commit_request = transaction->t_tid;
        jbd_debug(1, "woke because of timeout\n");
    }
    goto loop;

end_loop:
    spin_unlock(&journal->j_state_lock);
    del_timer_sync(&journal->j_commit_timer);
    journal->j_task = NULL;
    wake_up(&journal->j_wait_done_commit);
    jbd_debug(1, "Journal thread exiting.\n");
    return 0;
}

static int journal_start_thread(journal_t *journal)
{
    struct task_struct *t;

    t = kthread_run(kjournald, journal, "kjournald");
    if (IS_ERR(t))
        return PTR_ERR(t);

    wait_event(journal->j_wait_done_commit, journal->j_task != NULL);
    return 0;
}

static void journal_kill_thread(journal_t *journal)
{
    spin_lock(&journal->j_state_lock);
    journal->j_flags |= JFS_UNMOUNT;

    while (journal->j_task) {
        wake_up(&journal->j_wait_commit);
        spin_unlock(&journal->j_state_lock);
        wait_event(journal->j_wait_done_commit,
                journal->j_task == NULL);
        spin_lock(&journal->j_state_lock);
    }
    spin_unlock(&journal->j_state_lock);
}

/*
 * journal_write_metadata_buffer: write a metadata buffer to the journal.
 *
 * Writes a metadata buffer to a given disk block.  The actual IO is not
 * performed but a new buffer_head is constructed which labels the data
 * to be written with the correct destination disk block.
 *
 * Any magic-number escaping which needs to be done will cause a
 * copy-out here.  If the buffer happens to start with the
 * JFS_MAGIC_NUMBER, then we can't write it to the log directly: the
 * magic number is only written to the log for descripter blocks.  In
 * this case, we copy the data and replace the first word with 0, and we
 * return a result code which indicates that this buffer needs to be
 * marked as an escaped buffer in the corresponding log descriptor
 * block.  The missing word can then be restored when the block is read
 * during recovery.
 *
 * If the source buffer has already been modified by a new transaction
 * since we took the last commit snapshot, we use the frozen copy of
 * that data for IO.  If we end up using the existing buffer_head's data
 * for the write, then we *have* to lock the buffer to prevent anyone
 * else from using and possibly modifying it while the IO is in
 * progress.
 *
 * The function returns a pointer to the buffer_heads to be used for IO.
 *
 * We assume that the journal has already been locked in this function.
 *
 * Return value:
 *  <0: Error
 * >=0: Finished OK
 *
 * On success:
 * Bit 0 set == escape performed on the data
 * Bit 1 set == buffer copy-out performed (kfree the data after IO)
 */

int journal_write_metadata_buffer(transaction_t *transaction,
                  struct journal_head  *jh_in,
                  struct journal_head **jh_out,
                  unsigned int blocknr)
{
    int need_copy_out = 0;
    int done_copy_out = 0;
    int do_escape = 0;
    char *mapped_data;
    struct buffer_head *new_bh;
    struct journal_head *new_jh;
    struct page *new_page;
    unsigned int new_offset;
    struct buffer_head *bh_in = jh2bh(jh_in);
    journal_t *journal = transaction->t_journal;

    /*
     * The buffer really shouldn't be locked: only the current committing
     * transaction is allowed to write it, so nobody else is allowed
     * to do any IO.
     *
     * akpm: except if we're journalling data, and write() output is
     * also part of a shared mapping, and another thread has
     * decided to launch a writepage() against this buffer.
     */
    J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));

    new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
    /* keep subsequent assertions sane */
    new_bh->b_state = 0;
    init_buffer(new_bh, NULL, NULL);
    atomic_set(&new_bh->b_count, 1);
    new_jh = journal_add_journal_head(new_bh);  /* This sleeps */

    /*
     * If a new transaction has already done a buffer copy-out, then
     * we use that version of the data for the commit.
     */
    jbd_lock_bh_state(bh_in);
repeat:
    if (jh_in->b_frozen_data) {
        done_copy_out = 1;
        new_page = virt_to_page(jh_in->b_frozen_data);
        new_offset = offset_in_page(jh_in->b_frozen_data);
    } else {
        new_page = jh2bh(jh_in)->b_page;
        new_offset = offset_in_page(jh2bh(jh_in)->b_data);
    }

    mapped_data = kmap_atomic(new_page);
    /*
     * Check for escaping
     */
    if (*((__be32 *)(mapped_data + new_offset)) ==
                cpu_to_be32(JFS_MAGIC_NUMBER)) {
        need_copy_out = 1;
        do_escape = 1;
    }
    kunmap_atomic(mapped_data);

    /*
     * Do we need to do a data copy?
     */
    if (need_copy_out && !done_copy_out) {
        char *tmp;

        jbd_unlock_bh_state(bh_in);
        tmp = jbd_alloc(bh_in->b_size, GFP_NOFS);
        jbd_lock_bh_state(bh_in);
        if (jh_in->b_frozen_data) {
            jbd_free(tmp, bh_in->b_size);
            goto repeat;
        }

        jh_in->b_frozen_data = tmp;
        mapped_data = kmap_atomic(new_page);
        memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
        kunmap_atomic(mapped_data);

        new_page = virt_to_page(tmp);
        new_offset = offset_in_page(tmp);
        done_copy_out = 1;
    }

    /*
     * Did we need to do an escaping?  Now we've done all the
     * copying, we can finally do so.
     */
    if (do_escape) {
        mapped_data = kmap_atomic(new_page);
        *((unsigned int *)(mapped_data + new_offset)) = 0;
        kunmap_atomic(mapped_data);
    }

    set_bh_page(new_bh, new_page, new_offset);
    new_jh->b_transaction = NULL;
    new_bh->b_size = jh2bh(jh_in)->b_size;
    new_bh->b_bdev = transaction->t_journal->j_dev;
    new_bh->b_blocknr = blocknr;
    set_buffer_mapped(new_bh);
    set_buffer_dirty(new_bh);

    *jh_out = new_jh;

    /*
     * The to-be-written buffer needs to get moved to the io queue,
     * and the original buffer whose contents we are shadowing or
     * copying is moved to the transaction's shadow queue.
     */
    JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
    spin_lock(&journal->j_list_lock);
    __journal_file_buffer(jh_in, transaction, BJ_Shadow);
    spin_unlock(&journal->j_list_lock);
    jbd_unlock_bh_state(bh_in);

    JBUFFER_TRACE(new_jh, "file as BJ_IO");
    journal_file_buffer(new_jh, transaction, BJ_IO);

    return do_escape | (done_copy_out << 1);
}

/*
 * Allocation code for the journal file.  Manage the space left in the
 * journal, so that we can begin checkpointing when appropriate.
 */

/*
 * __log_space_left: Return the number of free blocks left in the journal.
 *
 * Called with the journal already locked.
 *
 * Called under j_state_lock
 */

int __log_space_left(journal_t *journal)
{
    int left = journal->j_free;

    assert_spin_locked(&journal->j_state_lock);

    /*
     * Be pessimistic here about the number of those free blocks which
     * might be required for log descriptor control blocks.
     */

#define MIN_LOG_RESERVED_BLOCKS 32 /* Allow for rounding errors */

    left -= MIN_LOG_RESERVED_BLOCKS;

    if (left <= 0)
        return 0;
    left -= (left >> 3);
    return left;
}

/*
 * Called under j_state_lock.  Returns true if a transaction commit was started.
 */
int __log_start_commit(journal_t *journal, tid_t target)
{
    /*
     * The only transaction we can possibly wait upon is the
     * currently running transaction (if it exists).  Otherwise,
     * the target tid must be an old one.
     */
    if (journal->j_running_transaction &&
        journal->j_running_transaction->t_tid == target) {
        /*
         * We want a new commit: OK, mark the request and wakeup the
         * commit thread.  We do _not_ do the commit ourselves.
         */

        journal->j_commit_request = target;
        jbd_debug(1, "JBD: requesting commit %d/%d\n",
              journal->j_commit_request,
              journal->j_commit_sequence);
        wake_up(&journal->j_wait_commit);
        return 1;
    } else if (!tid_geq(journal->j_commit_request, target))
        /* This should never happen, but if it does, preserve
           the evidence before kjournald goes into a loop and
           increments j_commit_sequence beyond all recognition. */
        WARN_ONCE(1, "jbd: bad log_start_commit: %u %u %u %u\n",
            journal->j_commit_request, journal->j_commit_sequence,
            target, journal->j_running_transaction ?
            journal->j_running_transaction->t_tid : 0);
    return 0;
}

int log_start_commit(journal_t *journal, tid_t tid)
{
    int ret;

    spin_lock(&journal->j_state_lock);
    ret = __log_start_commit(journal, tid);
    spin_unlock(&journal->j_state_lock);
    return ret;
}

/*
 * Force and wait upon a commit if the calling process is not within
 * transaction.  This is used for forcing out undo-protected data which contains
 * bitmaps, when the fs is running out of space.
 *
 * We can only force the running transaction if we don't have an active handle;
 * otherwise, we will deadlock.
 *
 * Returns true if a transaction was started.
 */
int journal_force_commit_nested(journal_t *journal)
{
    transaction_t *transaction = NULL;
    tid_t tid;

    spin_lock(&journal->j_state_lock);
    if (journal->j_running_transaction && !current->journal_info) {
        transaction = journal->j_running_transaction;
        __log_start_commit(journal, transaction->t_tid);
    } else if (journal->j_committing_transaction)
        transaction = journal->j_committing_transaction;

    if (!transaction) {
        spin_unlock(&journal->j_state_lock);
        return 0;   /* Nothing to retry */
    }

    tid = transaction->t_tid;
    spin_unlock(&journal->j_state_lock);
    log_wait_commit(journal, tid);
    return 1;
}

/*
 * Start a commit of the current running transaction (if any).  Returns true
 * if a transaction is going to be committed (or is currently already
 * committing), and fills its tid in at *ptid
 */
int journal_start_commit(journal_t *journal, tid_t *ptid)
{
    int ret = 0;

    spin_lock(&journal->j_state_lock);
    if (journal->j_running_transaction) {
        tid_t tid = journal->j_running_transaction->t_tid;

        __log_start_commit(journal, tid);
        /* There's a running transaction and we've just made sure
         * it's commit has been scheduled. */
        if (ptid)
            *ptid = tid;
        ret = 1;
    } else if (journal->j_committing_transaction) {
        /*
         * If commit has been started, then we have to wait for
         * completion of that transaction.
         */
        if (ptid)
            *ptid = journal->j_committing_transaction->t_tid;
        ret = 1;
    }
    spin_unlock(&journal->j_state_lock);
    return ret;
}

/*
 * Wait for a specified commit to complete.
 * The caller may not hold the journal lock.
 */
int log_wait_commit(journal_t *journal, tid_t tid)
{
    int err = 0;

#ifdef CONFIG_JBD_DEBUG
    spin_lock(&journal->j_state_lock);
    if (!tid_geq(journal->j_commit_request, tid)) {
        printk(KERN_EMERG
               "%s: error: j_commit_request=%d, tid=%d\n",
               __func__, journal->j_commit_request, tid);
    }
    spin_unlock(&journal->j_state_lock);
#endif
    spin_lock(&journal->j_state_lock);
    if (!tid_geq(journal->j_commit_waited, tid))
        journal->j_commit_waited = tid;
    while (tid_gt(tid, journal->j_commit_sequence)) {
        jbd_debug(1, "JBD: want %d, j_commit_sequence=%d\n",
                  tid, journal->j_commit_sequence);
        wake_up(&journal->j_wait_commit);
        spin_unlock(&journal->j_state_lock);
        wait_event(journal->j_wait_done_commit,
                !tid_gt(tid, journal->j_commit_sequence));
        spin_lock(&journal->j_state_lock);
    }
    spin_unlock(&journal->j_state_lock);

    if (unlikely(is_journal_aborted(journal))) {
        printk(KERN_EMERG "journal commit I/O error\n");
        err = -EIO;
    }
    return err;
}

/*
 * Return 1 if a given transaction has not yet sent barrier request
 * connected with a transaction commit. If 0 is returned, transaction
 * may or may not have sent the barrier. Used to avoid sending barrier
 * twice in common cases.
 */
int journal_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
{
    int ret = 0;
    transaction_t *commit_trans;

    if (!(journal->j_flags & JFS_BARRIER))
        return 0;
    spin_lock(&journal->j_state_lock);
    /* Transaction already committed? */
    if (tid_geq(journal->j_commit_sequence, tid))
        goto out;
    /*
     * Transaction is being committed and we already proceeded to
     * writing commit record?
     */
    commit_trans = journal->j_committing_transaction;
    if (commit_trans && commit_trans->t_tid == tid &&
        commit_trans->t_state >= T_COMMIT_RECORD)
        goto out;
    ret = 1;
out:
    spin_unlock(&journal->j_state_lock);
    return ret;
}
EXPORT_SYMBOL(journal_trans_will_send_data_barrier);

/*
 * Log buffer allocation routines:
 */

int journal_next_log_block(journal_t *journal, unsigned int *retp)
{
    unsigned int blocknr;

    spin_lock(&journal->j_state_lock);
    J_ASSERT(journal->j_free > 1);

    blocknr = journal->j_head;
    journal->j_head++;
    journal->j_free--;
    if (journal->j_head == journal->j_last)
        journal->j_head = journal->j_first;
    spin_unlock(&journal->j_state_lock);
    return journal_bmap(journal, blocknr, retp);
}

/*
 * Conversion of logical to physical block numbers for the journal
 *
 * On external journals the journal blocks are identity-mapped, so
 * this is a no-op.  If needed, we can use j_blk_offset - everything is
 * ready.
 */
int journal_bmap(journal_t *journal, unsigned int blocknr,
         unsigned int *retp)
{
    int err = 0;
    unsigned int ret;

    if (journal->j_inode) {
        ret = bmap(journal->j_inode, blocknr);
        if (ret)
            *retp = ret;
        else {
            char b[BDEVNAME_SIZE];

            printk(KERN_ALERT "%s: journal block not found "
                    "at offset %u on %s\n",
                __func__,
                blocknr,
                bdevname(journal->j_dev, b));
            err = -EIO;
            __journal_abort_soft(journal, err);
        }
    } else {
        *retp = blocknr; /* +journal->j_blk_offset */
    }
    return err;
}

/*
 * We play buffer_head aliasing tricks to write data/metadata blocks to
 * the journal without copying their contents, but for journal
 * descriptor blocks we do need to generate bona fide buffers.
 *
 * After the caller of journal_get_descriptor_buffer() has finished modifying
 * the buffer's contents they really should run flush_dcache_page(bh->b_page).
 * But we don't bother doing that, so there will be coherency problems with
 * mmaps of blockdevs which hold live JBD-controlled filesystems.
 */
struct journal_head *journal_get_descriptor_buffer(journal_t *journal)
{
    struct buffer_head *bh;
    unsigned int blocknr;
    int err;

    err = journal_next_log_block(journal, &blocknr);

    if (err)
        return NULL;

    bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
    if (!bh)
        return NULL;
    lock_buffer(bh);
    memset(bh->b_data, 0, journal->j_blocksize);
    set_buffer_uptodate(bh);
    unlock_buffer(bh);
    BUFFER_TRACE(bh, "return this buffer");
    return journal_add_journal_head(bh);
}

/*
 * Management for journal control blocks: functions to create and
 * destroy journal_t structures, and to initialise and read existing
 * journal blocks from disk.  */

/* First: create and setup a journal_t object in memory.  We initialise
 * very few fields yet: that has to wait until we have created the
 * journal structures from from scratch, or loaded them from disk. */

static journal_t * journal_init_common (void)
{
    journal_t *journal;
    int err;

    journal = kzalloc(sizeof(*journal), GFP_KERNEL);
    if (!journal)
        goto fail;

    init_waitqueue_head(&journal->j_wait_transaction_locked);
    init_waitqueue_head(&journal->j_wait_logspace);
    init_waitqueue_head(&journal->j_wait_done_commit);
    init_waitqueue_head(&journal->j_wait_checkpoint);
    init_waitqueue_head(&journal->j_wait_commit);
    init_waitqueue_head(&journal->j_wait_updates);
    mutex_init(&journal->j_checkpoint_mutex);
    spin_lock_init(&journal->j_revoke_lock);
    spin_lock_init(&journal->j_list_lock);
    spin_lock_init(&journal->j_state_lock);

    journal->j_commit_interval = (HZ * JBD_DEFAULT_MAX_COMMIT_AGE);

    /* The journal is marked for error until we succeed with recovery! */
    journal->j_flags = JFS_ABORT;

    /* Set up a default-sized revoke table for the new mount. */
    err = journal_init_revoke(journal, JOURNAL_REVOKE_DEFAULT_HASH);
    if (err) {
        kfree(journal);
        goto fail;
    }
    return journal;
fail:
    return NULL;
}

/* journal_init_dev and journal_init_inode:
 *
 * Create a journal structure assigned some fixed set of disk blocks to
 * the journal.  We don't actually touch those disk blocks yet, but we
 * need to set up all of the mapping information to tell the journaling
 * system where the journal blocks are.
 *
 */

journal_t * journal_init_dev(struct block_device *bdev,
            struct block_device *fs_dev,
            int start, int len, int blocksize)
{
    journal_t *journal = journal_init_common();
    struct buffer_head *bh;
    int n;

    if (!journal)
        return NULL;

    /* journal descriptor can store up to n blocks -bzzz */
    journal->j_blocksize = blocksize;
    n = journal->j_blocksize / sizeof(journal_block_tag_t);
    journal->j_wbufsize = n;
    journal->j_wbuf = kmalloc(n * sizeof(struct buffer_head*), GFP_KERNEL);
    if (!journal->j_wbuf) {
        printk(KERN_ERR "%s: Can't allocate bhs for commit thread\n",
            __func__);
        goto out_err;
    }
    journal->j_dev = bdev;
    journal->j_fs_dev = fs_dev;
    journal->j_blk_offset = start;
    journal->j_maxlen = len;

    bh = __getblk(journal->j_dev, start, journal->j_blocksize);
    if (!bh) {
        printk(KERN_ERR
               "%s: Cannot get buffer for journal superblock\n",
               __func__);
        goto out_err;
    }
    journal->j_sb_buffer = bh;
    journal->j_superblock = (journal_superblock_t *)bh->b_data;

    return journal;
out_err:
    kfree(journal->j_wbuf);
    kfree(journal);
    return NULL;
}

journal_t * journal_init_inode (struct inode *inode)
{
    struct buffer_head *bh;
    journal_t *journal = journal_init_common();
    int err;
    int n;
    unsigned int blocknr;

    if (!journal)
        return NULL;

    journal->j_dev = journal->j_fs_dev = inode->i_sb->s_bdev;
    journal->j_inode = inode;
    jbd_debug(1,
          "journal %p: inode %s/%ld, size %Ld, bits %d, blksize %ld\n",
          journal, inode->i_sb->s_id, inode->i_ino,
          (long long) inode->i_size,
          inode->i_sb->s_blocksize_bits, inode->i_sb->s_blocksize);

    journal->j_maxlen = inode->i_size >> inode->i_sb->s_blocksize_bits;
    journal->j_blocksize = inode->i_sb->s_blocksize;

    /* journal descriptor can store up to n blocks -bzzz */
    n = journal->j_blocksize / sizeof(journal_block_tag_t);
    journal->j_wbufsize = n;
    journal->j_wbuf = kmalloc(n * sizeof(struct buffer_head*), GFP_KERNEL);
    if (!journal->j_wbuf) {
        printk(KERN_ERR "%s: Can't allocate bhs for commit thread\n",
            __func__);
        goto out_err;
    }

    err = journal_bmap(journal, 0, &blocknr);
    /* If that failed, give up */
    if (err) {
        printk(KERN_ERR "%s: Cannot locate journal superblock\n",
               __func__);
        goto out_err;
    }

    bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
    if (!bh) {
        printk(KERN_ERR
               "%s: Cannot get buffer for journal superblock\n",
               __func__);
        goto out_err;
    }
    journal->j_sb_buffer = bh;
    journal->j_superblock = (journal_superblock_t *)bh->b_data;

    return journal;
out_err:
    kfree(journal->j_wbuf);
    kfree(journal);
    return NULL;
}

/*
 * If the journal init or create aborts, we need to mark the journal
 * superblock as being NULL to prevent the journal destroy from writing
 * back a bogus superblock.
 */
static void journal_fail_superblock (journal_t *journal)
{
    struct buffer_head *bh = journal->j_sb_buffer;
    brelse(bh);
    journal->j_sb_buffer = NULL;
}

/*
 * Given a journal_t structure, initialise the various fields for
 * startup of a new journaling session.  We use this both when creating
 * a journal, and after recovering an old journal to reset it for
 * subsequent use.
 */

static int journal_reset(journal_t *journal)
{
    journal_superblock_t *sb = journal->j_superblock;
    unsigned int first, last;

    first = be32_to_cpu(sb->s_first);
    last = be32_to_cpu(sb->s_maxlen);
    if (first + JFS_MIN_JOURNAL_BLOCKS > last + 1) {
        printk(KERN_ERR "JBD: Journal too short (blocks %u-%u).\n",
               first, last);
        journal_fail_superblock(journal);
        return -EINVAL;
    }

    journal->j_first = first;
    journal->j_last = last;

    journal->j_head = first;
    journal->j_tail = first;
    journal->j_free = last - first;

    journal->j_tail_sequence = journal->j_transaction_sequence;
    journal->j_commit_sequence = journal->j_transaction_sequence - 1;
    journal->j_commit_request = journal->j_commit_sequence;

    journal->j_max_transaction_buffers = journal->j_maxlen / 4;

    /*
     * As a special case, if the on-disk copy is already marked as needing
     * no recovery (s_start == 0), then we can safely defer the superblock
     * update until the next commit by setting JFS_FLUSHED.  This avoids
     * attempting a write to a potential-readonly device.
     */
    if (sb->s_start == 0) {
        jbd_debug(1,"JBD: Skipping superblock update on recovered sb "
            "(start %u, seq %d, errno %d)\n",
            journal->j_tail, journal->j_tail_sequence,
            journal->j_errno);
        journal->j_flags |= JFS_FLUSHED;
    } else {
        /* Lock here to make assertions happy... */
        mutex_lock(&journal->j_checkpoint_mutex);
        /*
         * Update log tail information. We use WRITE_FUA since new
         * transaction will start reusing journal space and so we
         * must make sure information about current log tail is on
         * disk before that.
         */
        journal_update_sb_log_tail(journal,
                       journal->j_tail_sequence,
                       journal->j_tail,
                       WRITE_FUA);
        mutex_unlock(&journal->j_checkpoint_mutex);
    }
    return journal_start_thread(journal);
}

int journal_create(journal_t *journal)
{
    unsigned int blocknr;
    struct buffer_head *bh;
    journal_superblock_t *sb;
    int i, err;

    if (journal->j_maxlen < JFS_MIN_JOURNAL_BLOCKS) {
        printk (KERN_ERR "Journal length (%d blocks) too short.\n",
            journal->j_maxlen);
        journal_fail_superblock(journal);
        return -EINVAL;
    }

    if (journal->j_inode == NULL) {
        /*
         * We don't know what block to start at!
         */
        printk(KERN_EMERG
               "%s: creation of journal on external device!\n",
               __func__);
        BUG();
    }

    /* Zero out the entire journal on disk.  We cannot afford to
       have any blocks on disk beginning with JFS_MAGIC_NUMBER. */
    jbd_debug(1, "JBD: Zeroing out journal blocks...\n");
    for (i = 0; i < journal->j_maxlen; i++) {
        err = journal_bmap(journal, i, &blocknr);
        if (err)
            return err;
        bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
        if (unlikely(!bh))
            return -ENOMEM;
        lock_buffer(bh);
        memset (bh->b_data, 0, journal->j_blocksize);
        BUFFER_TRACE(bh, "marking dirty");
        mark_buffer_dirty(bh);
        BUFFER_TRACE(bh, "marking uptodate");
        set_buffer_uptodate(bh);
        unlock_buffer(bh);
        __brelse(bh);
    }

    sync_blockdev(journal->j_dev);
    jbd_debug(1, "JBD: journal cleared.\n");

    /* OK, fill in the initial static fields in the new superblock */
    sb = journal->j_superblock;

    sb->s_header.h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
    sb->s_header.h_blocktype = cpu_to_be32(JFS_SUPERBLOCK_V2);

    sb->s_blocksize = cpu_to_be32(journal->j_blocksize);
    sb->s_maxlen    = cpu_to_be32(journal->j_maxlen);
    sb->s_first = cpu_to_be32(1);

    journal->j_transaction_sequence = 1;

    journal->j_flags &= ~JFS_ABORT;
    journal->j_format_version = 2;

    return journal_reset(journal);
}

static void journal_write_superblock(journal_t *journal, int write_op)
{
    struct buffer_head *bh = journal->j_sb_buffer;
    int ret;

    trace_journal_write_superblock(journal, write_op);
    if (!(journal->j_flags & JFS_BARRIER))
        write_op &= ~(REQ_FUA | REQ_FLUSH);
    lock_buffer(bh);
    if (buffer_write_io_error(bh)) {
        char b[BDEVNAME_SIZE];
        /*
         * Oh, dear.  A previous attempt to write the journal
         * superblock failed.  This could happen because the
         * USB device was yanked out.  Or it could happen to
         * be a transient write error and maybe the block will
         * be remapped.  Nothing we can do but to retry the
         * write and hope for the best.
         */
        printk(KERN_ERR "JBD: previous I/O error detected "
               "for journal superblock update for %s.\n",
               journal_dev_name(journal, b));
        clear_buffer_write_io_error(bh);
        set_buffer_uptodate(bh);
    }

    get_bh(bh);
    bh->b_end_io = end_buffer_write_sync;
    ret = submit_bh(write_op, bh);
    wait_on_buffer(bh);
    if (buffer_write_io_error(bh)) {
        clear_buffer_write_io_error(bh);
        set_buffer_uptodate(bh);
        ret = -EIO;
    }
    if (ret) {
        char b[BDEVNAME_SIZE];
        printk(KERN_ERR "JBD: Error %d detected "
               "when updating journal superblock for %s.\n",
               ret, journal_dev_name(journal, b));
    }
}

void journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
                unsigned int tail_block, int write_op)
{
    journal_superblock_t *sb = journal->j_superblock;

    BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
    jbd_debug(1,"JBD: updating superblock (start %u, seq %u)\n",
          tail_block, tail_tid);

    sb->s_sequence = cpu_to_be32(tail_tid);
    sb->s_start    = cpu_to_be32(tail_block);

    journal_write_superblock(journal, write_op);

    /* Log is no longer empty */
    spin_lock(&journal->j_state_lock);
    WARN_ON(!sb->s_sequence);
    journal->j_flags &= ~JFS_FLUSHED;
    spin_unlock(&journal->j_state_lock);
}

static void mark_journal_empty(journal_t *journal)
{
    journal_superblock_t *sb = journal->j_superblock;

    BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
    spin_lock(&journal->j_state_lock);
    /* Is it already empty? */
    if (sb->s_start == 0) {
        spin_unlock(&journal->j_state_lock);
        return;
    }
    jbd_debug(1, "JBD: Marking journal as empty (seq %d)\n",
              journal->j_tail_sequence);

    sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
    sb->s_start    = cpu_to_be32(0);
    spin_unlock(&journal->j_state_lock);

    journal_write_superblock(journal, WRITE_FUA);

    spin_lock(&journal->j_state_lock);
    /* Log is empty */
    journal->j_flags |= JFS_FLUSHED;
    spin_unlock(&journal->j_state_lock);
}

static void journal_update_sb_errno(journal_t *journal)
{
    journal_superblock_t *sb = journal->j_superblock;

    spin_lock(&journal->j_state_lock);
    jbd_debug(1, "JBD: updating superblock error (errno %d)\n",
              journal->j_errno);
    sb->s_errno = cpu_to_be32(journal->j_errno);
    spin_unlock(&journal->j_state_lock);

    journal_write_superblock(journal, WRITE_SYNC);
}

/*
 * Read the superblock for a given journal, performing initial
 * validation of the format.
 */

static int journal_get_superblock(journal_t *journal)
{
    struct buffer_head *bh;
    journal_superblock_t *sb;
    int err = -EIO;

    bh = journal->j_sb_buffer;

    J_ASSERT(bh != NULL);
    if (!buffer_uptodate(bh)) {
        ll_rw_block(READ, 1, &bh);
        wait_on_buffer(bh);
        if (!buffer_uptodate(bh)) {
            printk (KERN_ERR
                "JBD: IO error reading journal superblock\n");
            goto out;
        }
    }

    sb = journal->j_superblock;

    err = -EINVAL;

    if (sb->s_header.h_magic != cpu_to_be32(JFS_MAGIC_NUMBER) ||
        sb->s_blocksize != cpu_to_be32(journal->j_blocksize)) {
        printk(KERN_WARNING "JBD: no valid journal superblock found\n");
        goto out;
    }

    switch(be32_to_cpu(sb->s_header.h_blocktype)) {
    case JFS_SUPERBLOCK_V1:
        journal->j_format_version = 1;
        break;
    case JFS_SUPERBLOCK_V2:
        journal->j_format_version = 2;
        break;
    default:
        printk(KERN_WARNING "JBD: unrecognised superblock format ID\n");
        goto out;
    }

    if (be32_to_cpu(sb->s_maxlen) < journal->j_maxlen)
        journal->j_maxlen = be32_to_cpu(sb->s_maxlen);
    else if (be32_to_cpu(sb->s_maxlen) > journal->j_maxlen) {
        printk (KERN_WARNING "JBD: journal file too short\n");
        goto out;
    }

    if (be32_to_cpu(sb->s_first) == 0 ||
        be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
        printk(KERN_WARNING
            "JBD: Invalid start block of journal: %u\n",
            be32_to_cpu(sb->s_first));
        goto out;
    }

    return 0;

out:
    journal_fail_superblock(journal);
    return err;
}

/*
 * Load the on-disk journal superblock and read the key fields into the
 * journal_t.
 */

static int load_superblock(journal_t *journal)
{
    int err;
    journal_superblock_t *sb;

    err = journal_get_superblock(journal);
    if (err)
        return err;

    sb = journal->j_superblock;

    journal->j_tail_sequence = be32_to_cpu(sb->s_sequence);
    journal->j_tail = be32_to_cpu(sb->s_start);
    journal->j_first = be32_to_cpu(sb->s_first);
    journal->j_last = be32_to_cpu(sb->s_maxlen);
    journal->j_errno = be32_to_cpu(sb->s_errno);

    return 0;
}


int journal_load(journal_t *journal)
{
    int err;
    journal_superblock_t *sb;

    err = load_superblock(journal);
    if (err)
        return err;

    sb = journal->j_superblock;
    /* If this is a V2 superblock, then we have to check the
     * features flags on it. */

    if (journal->j_format_version >= 2) {
        if ((sb->s_feature_ro_compat &
             ~cpu_to_be32(JFS_KNOWN_ROCOMPAT_FEATURES)) ||
            (sb->s_feature_incompat &
             ~cpu_to_be32(JFS_KNOWN_INCOMPAT_FEATURES))) {
            printk (KERN_WARNING
                "JBD: Unrecognised features on journal\n");
            return -EINVAL;
        }
    }

    /* Let the recovery code check whether it needs to recover any
     * data from the journal. */
    if (journal_recover(journal))
        goto recovery_error;

    /* OK, we've finished with the dynamic journal bits:
     * reinitialise the dynamic contents of the superblock in memory
     * and reset them on disk. */
    if (journal_reset(journal))
        goto recovery_error;

    journal->j_flags &= ~JFS_ABORT;
    journal->j_flags |= JFS_LOADED;
    return 0;

recovery_error:
    printk (KERN_WARNING "JBD: recovery failed\n");
    return -EIO;
}

int journal_destroy(journal_t *journal)
{
    int err = 0;

    
    /* Wait for the commit thread to wake up and die. */
    journal_kill_thread(journal);

    /* Force a final log commit */
    if (journal->j_running_transaction)
        journal_commit_transaction(journal);

    /* Force any old transactions to disk */

    /* We cannot race with anybody but must keep assertions happy */
    mutex_lock(&journal->j_checkpoint_mutex);
    /* Totally anal locking here... */
    spin_lock(&journal->j_list_lock);
    while (journal->j_checkpoint_transactions != NULL) {
        spin_unlock(&journal->j_list_lock);
        log_do_checkpoint(journal);
        spin_lock(&journal->j_list_lock);
    }

    J_ASSERT(journal->j_running_transaction == NULL);
    J_ASSERT(journal->j_committing_transaction == NULL);
    J_ASSERT(journal->j_checkpoint_transactions == NULL);
    spin_unlock(&journal->j_list_lock);

    if (journal->j_sb_buffer) {
        if (!is_journal_aborted(journal)) {
            journal->j_tail_sequence =
                ++journal->j_transaction_sequence;
            mark_journal_empty(journal);
        } else
            err = -EIO;
        brelse(journal->j_sb_buffer);
    }
    mutex_unlock(&journal->j_checkpoint_mutex);

    if (journal->j_inode)
        iput(journal->j_inode);
    if (journal->j_revoke)
        journal_destroy_revoke(journal);
    kfree(journal->j_wbuf);
    kfree(journal);

    return err;
}


int journal_check_used_features (journal_t *journal, unsigned long compat,
                 unsigned long ro, unsigned long incompat)
{
    journal_superblock_t *sb;

    if (!compat && !ro && !incompat)
        return 1;
    if (journal->j_format_version == 1)
        return 0;

    sb = journal->j_superblock;

    if (((be32_to_cpu(sb->s_feature_compat) & compat) == compat) &&
        ((be32_to_cpu(sb->s_feature_ro_compat) & ro) == ro) &&
        ((be32_to_cpu(sb->s_feature_incompat) & incompat) == incompat))
        return 1;

    return 0;
}

int journal_check_available_features (journal_t *journal, unsigned long compat,
                      unsigned long ro, unsigned long incompat)
{
    if (!compat && !ro && !incompat)
        return 1;

    /* We can support any known requested features iff the
     * superblock is in version 2.  Otherwise we fail to support any
     * extended sb features. */

    if (journal->j_format_version != 2)
        return 0;

    if ((compat   & JFS_KNOWN_COMPAT_FEATURES) == compat &&
        (ro       & JFS_KNOWN_ROCOMPAT_FEATURES) == ro &&
        (incompat & JFS_KNOWN_INCOMPAT_FEATURES) == incompat)
        return 1;

    return 0;
}

int journal_set_features (journal_t *journal, unsigned long compat,
              unsigned long ro, unsigned long incompat)
{
    journal_superblock_t *sb;

    if (journal_check_used_features(journal, compat, ro, incompat))
        return 1;

    if (!journal_check_available_features(journal, compat, ro, incompat))
        return 0;

    jbd_debug(1, "Setting new features 0x%lx/0x%lx/0x%lx\n",
          compat, ro, incompat);

    sb = journal->j_superblock;

    sb->s_feature_compat    |= cpu_to_be32(compat);
    sb->s_feature_ro_compat |= cpu_to_be32(ro);
    sb->s_feature_incompat  |= cpu_to_be32(incompat);

    return 1;
}


int journal_update_format (journal_t *journal)
{
    journal_superblock_t *sb;
    int err;

    err = journal_get_superblock(journal);
    if (err)
        return err;

    sb = journal->j_superblock;

    switch (be32_to_cpu(sb->s_header.h_blocktype)) {
    case JFS_SUPERBLOCK_V2:
        return 0;
    case JFS_SUPERBLOCK_V1:
        return journal_convert_superblock_v1(journal, sb);
    default:
        break;
    }
    return -EINVAL;
}

static int journal_convert_superblock_v1(journal_t *journal,
                     journal_superblock_t *sb)
{
    int offset, blocksize;
    struct buffer_head *bh;

    printk(KERN_WARNING
        "JBD: Converting superblock from version 1 to 2.\n");

    /* Pre-initialise new fields to zero */
    offset = ((char *) &(sb->s_feature_compat)) - ((char *) sb);
    blocksize = be32_to_cpu(sb->s_blocksize);
    memset(&sb->s_feature_compat, 0, blocksize-offset);

    sb->s_nr_users = cpu_to_be32(1);
    sb->s_header.h_blocktype = cpu_to_be32(JFS_SUPERBLOCK_V2);
    journal->j_format_version = 2;

    bh = journal->j_sb_buffer;
    BUFFER_TRACE(bh, "marking dirty");
    mark_buffer_dirty(bh);
    sync_dirty_buffer(bh);
    return 0;
}


int journal_flush(journal_t *journal)
{
    int err = 0;
    transaction_t *transaction = NULL;

    spin_lock(&journal->j_state_lock);

    /* Force everything buffered to the log... */
    if (journal->j_running_transaction) {
        transaction = journal->j_running_transaction;
        __log_start_commit(journal, transaction->t_tid);
    } else if (journal->j_committing_transaction)
        transaction = journal->j_committing_transaction;

    /* Wait for the log commit to complete... */
    if (transaction) {
        tid_t tid = transaction->t_tid;

        spin_unlock(&journal->j_state_lock);
        log_wait_commit(journal, tid);
    } else {
        spin_unlock(&journal->j_state_lock);
    }

    /* ...and flush everything in the log out to disk. */
    spin_lock(&journal->j_list_lock);
    while (!err && journal->j_checkpoint_transactions != NULL) {
        spin_unlock(&journal->j_list_lock);
        mutex_lock(&journal->j_checkpoint_mutex);
        err = log_do_checkpoint(journal);
        mutex_unlock(&journal->j_checkpoint_mutex);
        spin_lock(&journal->j_list_lock);
    }
    spin_unlock(&journal->j_list_lock);

    if (is_journal_aborted(journal))
        return -EIO;

    mutex_lock(&journal->j_checkpoint_mutex);
    cleanup_journal_tail(journal);

    /* Finally, mark the journal as really needing no recovery.
     * This sets s_start==0 in the underlying superblock, which is
     * the magic code for a fully-recovered superblock.  Any future
     * commits of data to the journal will restore the current
     * s_start value. */
    mark_journal_empty(journal);
    mutex_unlock(&journal->j_checkpoint_mutex);
    spin_lock(&journal->j_state_lock);
    J_ASSERT(!journal->j_running_transaction);
    J_ASSERT(!journal->j_committing_transaction);
    J_ASSERT(!journal->j_checkpoint_transactions);
    J_ASSERT(journal->j_head == journal->j_tail);
    J_ASSERT(journal->j_tail_sequence == journal->j_transaction_sequence);
    spin_unlock(&journal->j_state_lock);
    return 0;
}

int journal_wipe(journal_t *journal, int write)
{
    int err = 0;

    J_ASSERT (!(journal->j_flags & JFS_LOADED));

    err = load_superblock(journal);
    if (err)
        return err;

    if (!journal->j_tail)
        goto no_recovery;

    printk (KERN_WARNING "JBD: %s recovery information on journal\n",
        write ? "Clearing" : "Ignoring");

    err = journal_skip_recovery(journal);
    if (write) {
        /* Lock to make assertions happy... */
        mutex_lock(&journal->j_checkpoint_mutex);
        mark_journal_empty(journal);
        mutex_unlock(&journal->j_checkpoint_mutex);
    }

 no_recovery:
    return err;
}

/*
 * journal_dev_name: format a character string to describe on what
 * device this journal is present.
 */

static const char *journal_dev_name(journal_t *journal, char *buffer)
{
    struct block_device *bdev;

    if (journal->j_inode)
        bdev = journal->j_inode->i_sb->s_bdev;
    else
        bdev = journal->j_dev;

    return bdevname(bdev, buffer);
}

/*
 * Journal abort has very specific semantics, which we describe
 * for journal abort.
 *
 * Two internal function, which provide abort to te jbd layer
 * itself are here.
 */

/*
 * Quick version for internal journal use (doesn't lock the journal).
 * Aborts hard --- we mark the abort as occurred, but do _nothing_ else,
 * and don't attempt to make any other journal updates.
 */
static void __journal_abort_hard(journal_t *journal)
{
    transaction_t *transaction;
    char b[BDEVNAME_SIZE];

    if (journal->j_flags & JFS_ABORT)
        return;

    printk(KERN_ERR "Aborting journal on device %s.\n",
        journal_dev_name(journal, b));

    spin_lock(&journal->j_state_lock);
    journal->j_flags |= JFS_ABORT;
    transaction = journal->j_running_transaction;
    if (transaction)
        __log_start_commit(journal, transaction->t_tid);
    spin_unlock(&journal->j_state_lock);
}

/* Soft abort: record the abort error status in the journal superblock,
 * but don't do any other IO. */
static void __journal_abort_soft (journal_t *journal, int errno)
{
    if (journal->j_flags & JFS_ABORT)
        return;

    if (!journal->j_errno)
        journal->j_errno = errno;

    __journal_abort_hard(journal);

    if (errno)
        journal_update_sb_errno(journal);
}

void journal_abort(journal_t *journal, int errno)
{
    __journal_abort_soft(journal, errno);
}

int journal_errno(journal_t *journal)
{
    int err;

    spin_lock(&journal->j_state_lock);
    if (journal->j_flags & JFS_ABORT)
        err = -EROFS;
    else
        err = journal->j_errno;
    spin_unlock(&journal->j_state_lock);
    return err;
}

int journal_clear_err(journal_t *journal)
{
    int err = 0;

    spin_lock(&journal->j_state_lock);
    if (journal->j_flags & JFS_ABORT)
        err = -EROFS;
    else
        journal->j_errno = 0;
    spin_unlock(&journal->j_state_lock);
    return err;
}

void journal_ack_err(journal_t *journal)
{
    spin_lock(&journal->j_state_lock);
    if (journal->j_errno)
        journal->j_flags |= JFS_ACK_ERR;
    spin_unlock(&journal->j_state_lock);
}

int journal_blocks_per_page(struct inode *inode)
{
    return 1 << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
}

/*
 * Journal_head storage management
 */
static struct kmem_cache *journal_head_cache;
#ifdef CONFIG_JBD_DEBUG
static atomic_t nr_journal_heads = ATOMIC_INIT(0);
#endif

static int journal_init_journal_head_cache(void)
{
    int retval;

    J_ASSERT(journal_head_cache == NULL);
    journal_head_cache = kmem_cache_create("journal_head",
                sizeof(struct journal_head),
                0,      /* offset */
                SLAB_TEMPORARY, /* flags */
                NULL);      /* ctor */
    retval = 0;
    if (!journal_head_cache) {
        retval = -ENOMEM;
        printk(KERN_EMERG "JBD: no memory for journal_head cache\n");
    }
    return retval;
}

static void journal_destroy_journal_head_cache(void)
{
    if (journal_head_cache) {
        kmem_cache_destroy(journal_head_cache);
        journal_head_cache = NULL;
    }
}

/*
 * journal_head splicing and dicing
 */
static struct journal_head *journal_alloc_journal_head(void)
{
    struct journal_head *ret;

#ifdef CONFIG_JBD_DEBUG
    atomic_inc(&nr_journal_heads);
#endif
    ret = kmem_cache_alloc(journal_head_cache, GFP_NOFS);
    if (ret == NULL) {
        jbd_debug(1, "out of memory for journal_head\n");
        printk_ratelimited(KERN_NOTICE "ENOMEM in %s, retrying.\n",
                   __func__);

        while (ret == NULL) {
            yield();
            ret = kmem_cache_alloc(journal_head_cache, GFP_NOFS);
        }
    }
    return ret;
}

static void journal_free_journal_head(struct journal_head *jh)
{
#ifdef CONFIG_JBD_DEBUG
    atomic_dec(&nr_journal_heads);
    memset(jh, JBD_POISON_FREE, sizeof(*jh));
#endif
    kmem_cache_free(journal_head_cache, jh);
}

/*
 * A journal_head is attached to a buffer_head whenever JBD has an
 * interest in the buffer.
 *
 * Whenever a buffer has an attached journal_head, its ->b_state:BH_JBD bit
 * is set.  This bit is tested in core kernel code where we need to take
 * JBD-specific actions.  Testing the zeroness of ->b_private is not reliable
 * there.
 *
 * When a buffer has its BH_JBD bit set, its ->b_count is elevated by one.
 *
 * When a buffer has its BH_JBD bit set it is immune from being released by
 * core kernel code, mainly via ->b_count.
 *
 * A journal_head is detached from its buffer_head when the journal_head's
 * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
 * transaction (b_cp_transaction) hold their references to b_jcount.
 *
 * Various places in the kernel want to attach a journal_head to a buffer_head
 * _before_ attaching the journal_head to a transaction.  To protect the
 * journal_head in this situation, journal_add_journal_head elevates the
 * journal_head's b_jcount refcount by one.  The caller must call
 * journal_put_journal_head() to undo this.
 *
 * So the typical usage would be:
 *
 *  (Attach a journal_head if needed.  Increments b_jcount)
 *  struct journal_head *jh = journal_add_journal_head(bh);
 *  ...
 *      (Get another reference for transaction)
 *      journal_grab_journal_head(bh);
 *      jh->b_transaction = xxx;
 *      (Put original reference)
 *      journal_put_journal_head(jh);
 */

/*
 * Give a buffer_head a journal_head.
 *
 * May sleep.
 */
struct journal_head *journal_add_journal_head(struct buffer_head *bh)
{
    struct journal_head *jh;
    struct journal_head *new_jh = NULL;

repeat:
    if (!buffer_jbd(bh)) {
        new_jh = journal_alloc_journal_head();
        memset(new_jh, 0, sizeof(*new_jh));
    }

    jbd_lock_bh_journal_head(bh);
    if (buffer_jbd(bh)) {
        jh = bh2jh(bh);
    } else {
        J_ASSERT_BH(bh,
            (atomic_read(&bh->b_count) > 0) ||
            (bh->b_page && bh->b_page->mapping));

        if (!new_jh) {
            jbd_unlock_bh_journal_head(bh);
            goto repeat;
        }

        jh = new_jh;
        new_jh = NULL;      /* We consumed it */
        set_buffer_jbd(bh);
        bh->b_private = jh;
        jh->b_bh = bh;
        get_bh(bh);
        BUFFER_TRACE(bh, "added journal_head");
    }
    jh->b_jcount++;
    jbd_unlock_bh_journal_head(bh);
    if (new_jh)
        journal_free_journal_head(new_jh);
    return bh->b_private;
}

/*
 * Grab a ref against this buffer_head's journal_head.  If it ended up not
 * having a journal_head, return NULL
 */
struct journal_head *journal_grab_journal_head(struct buffer_head *bh)
{
    struct journal_head *jh = NULL;

    jbd_lock_bh_journal_head(bh);
    if (buffer_jbd(bh)) {
        jh = bh2jh(bh);
        jh->b_jcount++;
    }
    jbd_unlock_bh_journal_head(bh);
    return jh;
}

static void __journal_remove_journal_head(struct buffer_head *bh)
{
    struct journal_head *jh = bh2jh(bh);

    J_ASSERT_JH(jh, jh->b_jcount >= 0);
    J_ASSERT_JH(jh, jh->b_transaction == NULL);
    J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
    J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
    J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
    J_ASSERT_BH(bh, buffer_jbd(bh));
    J_ASSERT_BH(bh, jh2bh(jh) == bh);
    BUFFER_TRACE(bh, "remove journal_head");
    if (jh->b_frozen_data) {
        printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
        jbd_free(jh->b_frozen_data, bh->b_size);
    }
    if (jh->b_committed_data) {
        printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
        jbd_free(jh->b_committed_data, bh->b_size);
    }
    bh->b_private = NULL;
    jh->b_bh = NULL;    /* debug, really */
    clear_buffer_jbd(bh);
    journal_free_journal_head(jh);
}

/*
 * Drop a reference on the passed journal_head.  If it fell to zero then
 * release the journal_head from the buffer_head.
 */
void journal_put_journal_head(struct journal_head *jh)
{
    struct buffer_head *bh = jh2bh(jh);

    jbd_lock_bh_journal_head(bh);
    J_ASSERT_JH(jh, jh->b_jcount > 0);
    --jh->b_jcount;
    if (!jh->b_jcount) {
        __journal_remove_journal_head(bh);
        jbd_unlock_bh_journal_head(bh);
        __brelse(bh);
    } else
        jbd_unlock_bh_journal_head(bh);
}

/*
 * debugfs tunables
 */
#ifdef CONFIG_JBD_DEBUG

u8 journal_enable_debug __read_mostly;
EXPORT_SYMBOL(journal_enable_debug);

static struct dentry *jbd_debugfs_dir;
static struct dentry *jbd_debug;

static void __init jbd_create_debugfs_entry(void)
{
    jbd_debugfs_dir = debugfs_create_dir("jbd", NULL);
    if (jbd_debugfs_dir)
        jbd_debug = debugfs_create_u8("jbd-debug", S_IRUGO | S_IWUSR,
                           jbd_debugfs_dir,
                           &journal_enable_debug);
}

static void __exit jbd_remove_debugfs_entry(void)
{
    debugfs_remove(jbd_debug);
    debugfs_remove(jbd_debugfs_dir);
}

#else

static inline void jbd_create_debugfs_entry(void)
{
}

static inline void jbd_remove_debugfs_entry(void)
{
}

#endif

struct kmem_cache *jbd_handle_cache;

static int __init journal_init_handle_cache(void)
{
    jbd_handle_cache = kmem_cache_create("journal_handle",
                sizeof(handle_t),
                0,      /* offset */
                SLAB_TEMPORARY, /* flags */
                NULL);      /* ctor */
    if (jbd_handle_cache == NULL) {
        printk(KERN_EMERG "JBD: failed to create handle cache\n");
        return -ENOMEM;
    }
    return 0;
}

static void journal_destroy_handle_cache(void)
{
    if (jbd_handle_cache)
        kmem_cache_destroy(jbd_handle_cache);
}

/*
 * Module startup and shutdown
 */

static int __init journal_init_caches(void)
{
    int ret;

    ret = journal_init_revoke_caches();
    if (ret == 0)
        ret = journal_init_journal_head_cache();
    if (ret == 0)
        ret = journal_init_handle_cache();
    return ret;
}

static void journal_destroy_caches(void)
{
    journal_destroy_revoke_caches();
    journal_destroy_journal_head_cache();
    journal_destroy_handle_cache();
}

static int __init journal_init(void)
{
    int ret;

    BUILD_BUG_ON(sizeof(struct journal_superblock_s) != 1024);

    ret = journal_init_caches();
    if (ret != 0)
        journal_destroy_caches();
    jbd_create_debugfs_entry();
    return ret;
}

static void __exit journal_exit(void)
{
#ifdef CONFIG_JBD_DEBUG
    int n = atomic_read(&nr_journal_heads);
    if (n)
        printk(KERN_EMERG "JBD: leaked %d journal_heads!\n", n);
#endif
    jbd_remove_debugfs_entry();
    journal_destroy_caches();
}

MODULE_LICENSE("GPL");
module_init(journal_init);
module_exit(journal_exit);