Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/teigland/dlm

[linux-2.6] / fs / jbd / journal.c

/*
 * linux/fs/jbd/journal.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 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 <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_update_superblock);
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(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);

/*
 * 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);

        /* 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);
                refrigerator();
                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 long 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);

        /*
         * 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);

        /*
         * 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, KM_USER0);
        /*
         * 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, KM_USER0);

        /*
         * 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, KM_USER0);
                memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
                kunmap_atomic(mapped_data, KM_USER0);

                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, KM_USER0);
                *((unsigned int *)(mapped_data + new_offset)) = 0;
                kunmap_atomic(mapped_data, KM_USER0);
        }

        /* keep subsequent assertions sane */
        new_bh->b_state = 0;
        init_buffer(new_bh, NULL, NULL);
        atomic_set(&new_bh->b_count, 1);
        jbd_unlock_bh_state(bh_in);

        new_jh = journal_add_journal_head(new_bh);      /* This sleeps */

        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");
        journal_file_buffer(jh_in, transaction, BJ_Shadow);
        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 was started.
 */
int __log_start_commit(journal_t *journal, tid_t target)
{
        /*
         * Are we already doing a recent enough commit?
         */
        if (!tid_geq(journal->j_commit_request, target)) {
                /*
                 * We want a new commit: OK, mark the request and wakup 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;
        }
        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 was started, 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;

                ret = __log_start_commit(journal, tid);
                if (ret && ptid)
                        *ptid = tid;
        } else if (journal->j_committing_transaction && ptid) {
                /*
                 * If ext3_write_super() recently started a commit, then we
                 * have to wait for completion of that transaction
                 */
                *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",
                       __FUNCTION__, journal->j_commit_request, tid);
        }
        spin_unlock(&journal->j_state_lock);
#endif
        spin_lock(&journal->j_state_lock);
        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;
}

/*
 * Log buffer allocation routines:
 */

int journal_next_log_block(journal_t *journal, unsigned long *retp)
{
        unsigned long 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 long blocknr,
                 unsigned long *retp)
{
        int err = 0;
        unsigned long 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 %lu on %s\n",
                                __FUNCTION__,
                                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 long blocknr;
        int err;

        err = journal_next_log_block(journal, &blocknr);

        if (err)
                return NULL;

        bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
        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_barrier);
        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() - creates an initialises a journal structure
 *  @bdev: Block device on which to create the journal
 *  @fs_dev: Device which hold journalled filesystem for this journal.
 *  @start: Block nr Start of journal.
 *  @len:  Length of the journal in blocks.
 *  @blocksize: blocksize of journalling device
 *  @returns: a newly created journal_t *
 *
 *  journal_init_dev creates a journal which maps a fixed contiguous
 *  range of blocks on an arbitrary block device.
 *
 */
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: Cant allocate bhs for commit thread\n",
                        __FUNCTION__);
                kfree(journal);
                journal = NULL;
                goto out;
        }
        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);
        J_ASSERT(bh != NULL);
        journal->j_sb_buffer = bh;
        journal->j_superblock = (journal_superblock_t *)bh->b_data;
out:
        return journal;
}

/**
 *  journal_t * journal_init_inode () - creates a journal which maps to a inode.
 *  @inode: An inode to create the journal in
 *
 * journal_init_inode creates a journal which maps an on-disk inode as
 * the journal.  The inode must exist already, must support bmap() and
 * must have all data blocks preallocated.
 */
journal_t * journal_init_inode (struct inode *inode)
{
        struct buffer_head *bh;
        journal_t *journal = journal_init_common();
        int err;
        int n;
        unsigned long 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: Cant allocate bhs for commit thread\n",
                        __FUNCTION__);
                kfree(journal);
                return NULL;
        }

        err = journal_bmap(journal, 0, &blocknr);
        /* If that failed, give up */
        if (err) {
                printk(KERN_ERR "%s: Cannnot locate journal superblock\n",
                       __FUNCTION__);
                kfree(journal);
                return NULL;
        }

        bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
        J_ASSERT(bh != NULL);
        journal->j_sb_buffer = bh;
        journal->j_superblock = (journal_superblock_t *)bh->b_data;

        return journal;
}

/*
 * 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 long first, last;

        first = be32_to_cpu(sb->s_first);
        last = be32_to_cpu(sb->s_maxlen);

        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;

        /* Add the dynamic fields and write it to disk. */
        journal_update_superblock(journal, 1);
        return journal_start_thread(journal);
}

/**
 * int journal_create() - Initialise the new journal file
 * @journal: Journal to create. This structure must have been initialised
 *
 * Given a journal_t structure which tells us which disk blocks we can
 * use, create a new journal superblock and initialise all of the
 * journal fields from scratch.
 **/
int journal_create(journal_t *journal)
{
        unsigned long 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",
                       __FUNCTION__);
                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);
                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);
}

/**
 * void journal_update_superblock() - Update journal sb on disk.
 * @journal: The journal to update.
 * @wait: Set to '0' if you don't want to wait for IO completion.
 *
 * Update a journal's dynamic superblock fields and write it to disk,
 * optionally waiting for the IO to complete.
 */
void journal_update_superblock(journal_t *journal, int wait)
{
        journal_superblock_t *sb = journal->j_superblock;
        struct buffer_head *bh = journal->j_sb_buffer;

        /*
         * As a special case, if the on-disk copy is already marked as needing
         * no recovery (s_start == 0) and there are no outstanding transactions
         * in the filesystem, 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 && journal->j_tail_sequence ==
                                journal->j_transaction_sequence) {
                jbd_debug(1,"JBD: Skipping superblock update on recovered sb "
                        "(start %ld, seq %d, errno %d)\n",
                        journal->j_tail, journal->j_tail_sequence,
                        journal->j_errno);
                goto out;
        }

        spin_lock(&journal->j_state_lock);
        jbd_debug(1,"JBD: updating superblock (start %ld, seq %d, errno %d)\n",
                  journal->j_tail, journal->j_tail_sequence, journal->j_errno);

        sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
        sb->s_start    = cpu_to_be32(journal->j_tail);
        sb->s_errno    = cpu_to_be32(journal->j_errno);
        spin_unlock(&journal->j_state_lock);

        BUFFER_TRACE(bh, "marking dirty");
        mark_buffer_dirty(bh);
        if (wait)
                sync_dirty_buffer(bh);
        else
                ll_rw_block(SWRITE, 1, &bh);

out:
        /* If we have just flushed the log (by marking s_start==0), then
         * any future commit will have to be careful to update the
         * superblock again to re-record the true start of the log. */

        spin_lock(&journal->j_state_lock);
        if (sb->s_start)
                journal->j_flags &= ~JFS_FLUSHED;
        else
                journal->j_flags |= JFS_FLUSHED;
        spin_unlock(&journal->j_state_lock);
}

/*
 * 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;
        }

        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() - Read journal from disk.
 * @journal: Journal to act on.
 *
 * Given a journal_t structure which tells us which disk blocks contain
 * a journal, read the journal from disk to initialise the in-memory
 * structures.
 */
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;
}

/**
 * void journal_destroy() - Release a journal_t structure.
 * @journal: Journal to act on.
 *
 * Release a journal_t structure once it is no longer in use by the
 * journaled object.
 */
void journal_destroy(journal_t *journal)
{
        /* 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 */

        /* 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);

        /* We can now mark the journal as empty. */
        journal->j_tail = 0;
        journal->j_tail_sequence = ++journal->j_transaction_sequence;
        if (journal->j_sb_buffer) {
                journal_update_superblock(journal, 1);
                brelse(journal->j_sb_buffer);
        }

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


/**
 *int journal_check_used_features () - Check if features specified are used.
 * @journal: Journal to check.
 * @compat: bitmask of compatible features
 * @ro: bitmask of features that force read-only mount
 * @incompat: bitmask of incompatible features
 *
 * Check whether the journal uses all of a given set of
 * features.  Return true (non-zero) if it does.
 **/

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() - Check feature set in journalling layer
 * @journal: Journal to check.
 * @compat: bitmask of compatible features
 * @ro: bitmask of features that force read-only mount
 * @incompat: bitmask of incompatible features
 *
 * Check whether the journaling code supports the use of
 * all of a given set of features on this journal.  Return true
 * (non-zero) if it can. */

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

        if (!compat && !ro && !incompat)
                return 1;

        sb = journal->j_superblock;

        /* 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 () - Mark a given journal feature in the superblock
 * @journal: Journal to act on.
 * @compat: bitmask of compatible features
 * @ro: bitmask of features that force read-only mount
 * @incompat: bitmask of incompatible features
 *
 * Mark a given journal feature as present on the
 * superblock.  Returns true if the requested features could be set.
 *
 */

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 () - Update on-disk journal structure.
 * @journal: Journal to act on.
 *
 * Given an initialised but unloaded journal struct, poke about in the
 * on-disk structure to update it to the most recent supported version.
 */
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 () - Flush journal
 * @journal: Journal to act on.
 *
 * Flush all data for a given journal to disk and empty the journal.
 * Filesystems can use this when remounting readonly to ensure that
 * recovery does not need to happen on remount.
 */

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

        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);
                err = log_do_checkpoint(journal);
                spin_lock(&journal->j_list_lock);
        }
        spin_unlock(&journal->j_list_lock);
        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. */
        spin_lock(&journal->j_state_lock);
        old_tail = journal->j_tail;
        journal->j_tail = 0;
        spin_unlock(&journal->j_state_lock);
        journal_update_superblock(journal, 1);
        spin_lock(&journal->j_state_lock);
        journal->j_tail = old_tail;

        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 err;
}

/**
 * int journal_wipe() - Wipe journal contents
 * @journal: Journal to act on.
 * @write: flag (see below)
 *
 * Wipe out all of the contents of a journal, safely.  This will produce
 * a warning if the journal contains any valid recovery information.
 * Must be called between journal_init_*() and journal_load().
 *
 * If 'write' is non-zero, then we wipe out the journal on disk; otherwise
 * we merely suppress recovery.
 */

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

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

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

        sb = journal->j_superblock;

        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)
                journal_update_superblock(journal, 1);

 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_superblock(journal, 1);
}

/**
 * void journal_abort () - Shutdown the journal immediately.
 * @journal: the journal to shutdown.
 * @errno:   an error number to record in the journal indicating
 *           the reason for the shutdown.
 *
 * Perform a complete, immediate shutdown of the ENTIRE
 * journal (not of a single transaction).  This operation cannot be
 * undone without closing and reopening the journal.
 *
 * The journal_abort function is intended to support higher level error
 * recovery mechanisms such as the ext2/ext3 remount-readonly error
 * mode.
 *
 * Journal abort has very specific semantics.  Any existing dirty,
 * unjournaled buffers in the main filesystem will still be written to
 * disk by bdflush, but the journaling mechanism will be suspended
 * immediately and no further transaction commits will be honoured.
 *
 * Any dirty, journaled buffers will be written back to disk without
 * hitting the journal.  Atomicity cannot be guaranteed on an aborted
 * filesystem, but we _do_ attempt to leave as much data as possible
 * behind for fsck to use for cleanup.
 *
 * Any attempt to get a new transaction handle on a journal which is in
 * ABORT state will just result in an -EROFS error return.  A
 * journal_stop on an existing handle will return -EIO if we have
 * entered abort state during the update.
 *
 * Recursive transactions are not disturbed by journal abort until the
 * final journal_stop, which will receive the -EIO error.
 *
 * Finally, the journal_abort call allows the caller to supply an errno
 * which will be recorded (if possible) in the journal superblock.  This
 * allows a client to record failure conditions in the middle of a
 * transaction without having to complete the transaction to record the
 * failure to disk.  ext3_error, for example, now uses this
 * functionality.
 *
 * Errors which originate from within the journaling layer will NOT
 * supply an errno; a null errno implies that absolutely no further
 * writes are done to the journal (unless there are any already in
 * progress).
 *
 */

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

/**
 * int journal_errno () - returns the journal's error state.
 * @journal: journal to examine.
 *
 * This is the errno numbet set with journal_abort(), the last
 * time the journal was mounted - if the journal was stopped
 * without calling abort this will be 0.
 *
 * If the journal has been aborted on this mount time -EROFS will
 * be returned.
 */
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 () - clears the journal's error state
 * @journal: journal to act on.
 *
 * An error must be cleared or Acked to take a FS out of readonly
 * mode.
 */
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() - Ack journal err.
 * @journal: journal to act on.
 *
 * An error must be cleared or Acked to take a FS out of readonly
 * mode.
 */
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 == 0);
        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 == 0) {
                retval = -ENOMEM;
                printk(KERN_EMERG "JBD: no memory for journal_head cache\n");
        }
        return retval;
}

static void journal_destroy_journal_head_cache(void)
{
        J_ASSERT(journal_head_cache != NULL);
        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;
        static unsigned long last_warning;

#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");
                if (time_after(jiffies, last_warning + 5*HZ)) {
                        printk(KERN_NOTICE "ENOMEM in %s, retrying.\n",
                               __FUNCTION__);
                        last_warning = jiffies;
                }
                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 may be detached from its buffer_head when the journal_head's
 * b_transaction, b_cp_transaction and b_next_transaction pointers are NULL.
 * Various places in JBD call journal_remove_journal_head() to indicate that the
 * journal_head can be dropped if needed.
 *
 * 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);
 *      ...
 *      jh->b_transaction = xxx;
 *      journal_put_journal_head(jh);
 *
 * Now, the journal_head's b_jcount is zero, but it is safe from being released
 * because it has a non-zero b_transaction.
 */

/*
 * Give a buffer_head a journal_head.
 *
 * Doesn't need the journal lock.
 * 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);

        get_bh(bh);
        if (jh->b_jcount == 0) {
                if (jh->b_transaction == NULL &&
                                jh->b_next_transaction == NULL &&
                                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",
                                                __FUNCTION__);
                                jbd_free(jh->b_frozen_data, bh->b_size);
                        }
                        if (jh->b_committed_data) {
                                printk(KERN_WARNING "%s: freeing "
                                                "b_committed_data\n",
                                                __FUNCTION__);
                                jbd_free(jh->b_committed_data, bh->b_size);
                        }
                        bh->b_private = NULL;
                        jh->b_bh = NULL;        /* debug, really */
                        clear_buffer_jbd(bh);
                        __brelse(bh);
                        journal_free_journal_head(jh);
                } else {
                        BUFFER_TRACE(bh, "journal_head was locked");
                }
        }
}

/*
 * journal_remove_journal_head(): if the buffer isn't attached to a transaction
 * and has a zero b_jcount then remove and release its journal_head.   If we did
 * see that the buffer is not used by any transaction we also "logically"
 * decrement ->b_count.
 *
 * We in fact take an additional increment on ->b_count as a convenience,
 * because the caller usually wants to do additional things with the bh
 * after calling here.
 * The caller of journal_remove_journal_head() *must* run __brelse(bh) at some
 * time.  Once the caller has run __brelse(), the buffer is eligible for
 * reaping by try_to_free_buffers().
 */
void journal_remove_journal_head(struct buffer_head *bh)
{
        jbd_lock_bh_journal_head(bh);
        __journal_remove_journal_head(bh);
        jbd_unlock_bh_journal_head(bh);
}

/*
 * Drop a reference on the passed journal_head.  If it fell to zero then try to
 * 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 && !jh->b_transaction) {
                __journal_remove_journal_head(bh);
                __brelse(bh);
        }
        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,
                                               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);