[PATCH] jbd2: initial copy of files from jbd

This is a simple copy of the files in fs/jbd to fs/jbd2 and
/usr/incude/linux/[ext4_]jbd.h to /usr/include/[ext4_]jbd2.h

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2072 insertions, 0 deletions

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
new file mode 100644
index 000000000000..c518dd8fe60a
--- /dev/null
+++ b/fs/jbd2/journal.c
@@ -0,0 +1,2072 @@
+/*
+ * 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/smp_lock.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/suspend.h>
+#include <linux/pagemap.h>
+#include <linux/kthread.h>
+#include <linux/poison.h>
+#include <linux/proc_fs.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);
+static int journal_create_jbd_slab(size_t slab_size);
+
+/*
+ * 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 void journal_start_thread(journal_t *journal)
+{
+        kthread_run(kjournald, journal, "kjournald");
+        wait_event(journal->j_wait_done_commit, journal->j_task != 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 == 0);
+                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_slab_alloc(bh_in->b_size, GFP_NOFS);
+                jbd_lock_bh_state(bh_in);
+                if (jh_in->b_frozen_data) {
+                        jbd_slab_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 = jbd_kmalloc(sizeof(*journal), GFP_KERNEL);
+        if (!journal)
+                goto fail;
+        memset(journal, 0, sizeof(*journal));
+
+        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;
+        }
+        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;
+
+        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);
+        journal_start_thread(journal);
+        return 0;
+}
+
+/**
+ * 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;
+                }
+        }
+
+        /*
+         * Create a slab for this blocksize
+         */
+        err = journal_create_jbd_slab(be32_to_cpu(sb->s_blocksize));
+        if (err)
+                return err;
+
+        /* 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.
+ */
+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);
+}
+
+/*
+ * Simple support for retrying memory allocations.  Introduced to help to
+ * debug different VM deadlock avoidance strategies.
+ */
+void * __jbd_kmalloc (const char *where, size_t size, gfp_t flags, int retry)
+{
+        return kmalloc(size, flags | (retry ? __GFP_NOFAIL : 0));
+}
+
+/*
+ * jbd slab management: create 1k, 2k, 4k, 8k slabs as needed
+ * and allocate frozen and commit buffers from these slabs.
+ *
+ * Reason for doing this is to avoid, SLAB_DEBUG - since it could
+ * cause bh to cross page boundary.
+ */
+
+#define JBD_MAX_SLABS 5
+#define JBD_SLAB_INDEX(size)  (size >> 11)
+
+static kmem_cache_t *jbd_slab[JBD_MAX_SLABS];
+static const char *jbd_slab_names[JBD_MAX_SLABS] = {
+        "jbd_1k", "jbd_2k", "jbd_4k", NULL, "jbd_8k"
+};
+
+static void journal_destroy_jbd_slabs(void)
+{
+        int i;
+
+        for (i = 0; i < JBD_MAX_SLABS; i++) {
+                if (jbd_slab[i])
+                        kmem_cache_destroy(jbd_slab[i]);
+                jbd_slab[i] = NULL;
+        }
+}
+
+static int journal_create_jbd_slab(size_t slab_size)
+{
+        int i = JBD_SLAB_INDEX(slab_size);
+
+        BUG_ON(i >= JBD_MAX_SLABS);
+
+        /*
+         * Check if we already have a slab created for this size
+         */
+        if (jbd_slab[i])
+                return 0;
+
+        /*
+         * Create a slab and force alignment to be same as slabsize -
+         * this will make sure that allocations won't cross the page
+         * boundary.
+         */
+        jbd_slab[i] = kmem_cache_create(jbd_slab_names[i],
+                                slab_size, slab_size, 0, NULL, NULL);
+        if (!jbd_slab[i]) {
+                printk(KERN_EMERG "JBD: no memory for jbd_slab cache\n");
+                return -ENOMEM;
+        }
+        return 0;
+}
+
+void * jbd_slab_alloc(size_t size, gfp_t flags)
+{
+        int idx;
+
+        idx = JBD_SLAB_INDEX(size);
+        BUG_ON(jbd_slab[idx] == NULL);
+        return kmem_cache_alloc(jbd_slab[idx], flags | __GFP_NOFAIL);
+}
+
+void jbd_slab_free(void *ptr,  size_t size)
+{
+        int idx;
+
+        idx = JBD_SLAB_INDEX(size);
+        BUG_ON(jbd_slab[idx] == NULL);
+        kmem_cache_free(jbd_slab[idx], ptr);
+}
+
+/*
+ * Journal_head storage management
+ */
+static kmem_cache_t *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 */
+                                0,              /* flags */
+                                NULL,           /* ctor */
+                                NULL);          /* dtor */
+        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 == 0) {
+                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 == 0) {
+                        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_slab_free(jh->b_frozen_data, bh->b_size);
+                        }
+                        if (jh->b_committed_data) {
+                                printk(KERN_WARNING "%s: freeing "
+                                                "b_committed_data\n",
+                                                __FUNCTION__);
+                                jbd_slab_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);
+}
+
+/*
+ * /proc tunables
+ */
+#if defined(CONFIG_JBD_DEBUG)
+int journal_enable_debug;
+EXPORT_SYMBOL(journal_enable_debug);
+#endif
+
+#if defined(CONFIG_JBD_DEBUG) && defined(CONFIG_PROC_FS)
+
+static struct proc_dir_entry *proc_jbd_debug;
+
+static int read_jbd_debug(char *page, char **start, off_t off,
+                          int count, int *eof, void *data)
+{
+        int ret;
+
+        ret = sprintf(page + off, "%d\n", journal_enable_debug);
+        *eof = 1;
+        return ret;
+}
+
+static int write_jbd_debug(struct file *file, const char __user *buffer,
+                           unsigned long count, void *data)
+{
+        char buf[32];
+
+        if (count > ARRAY_SIZE(buf) - 1)
+                count = ARRAY_SIZE(buf) - 1;
+        if (copy_from_user(buf, buffer, count))
+                return -EFAULT;
+        buf[ARRAY_SIZE(buf) - 1] = '\0';
+        journal_enable_debug = simple_strtoul(buf, NULL, 10);
+        return count;
+}
+
+#define JBD_PROC_NAME "sys/fs/jbd-debug"
+
+static void __init create_jbd_proc_entry(void)
+{
+        proc_jbd_debug = create_proc_entry(JBD_PROC_NAME, 0644, NULL);
+        if (proc_jbd_debug) {
+                /* Why is this so hard? */
+                proc_jbd_debug->read_proc = read_jbd_debug;
+                proc_jbd_debug->write_proc = write_jbd_debug;
+        }
+}
+
+static void __exit remove_jbd_proc_entry(void)
+{
+        if (proc_jbd_debug)
+                remove_proc_entry(JBD_PROC_NAME, NULL);
+}
+
+#else
+
+#define create_jbd_proc_entry() do {} while (0)
+#define remove_jbd_proc_entry() do {} while (0)
+
+#endif
+
+kmem_cache_t *jbd_handle_cache;
+
+static int __init journal_init_handle_cache(void)
+{
+        jbd_handle_cache = kmem_cache_create("journal_handle",
+                                sizeof(handle_t),
+                                0,              /* offset */
+                                0,              /* flags */
+                                NULL,           /* ctor */
+                                NULL);          /* dtor */
+        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();
+        journal_destroy_jbd_slabs();
+}
+
+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();
+        create_jbd_proc_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
+        remove_jbd_proc_entry();
+        journal_destroy_caches();
+}
+
+MODULE_LICENSE("GPL");
+module_init(journal_init);
+module_exit(journal_exit);
+