Cross-Referenced Linux and Device Driver Code

   /*
    * linux/fs/jbd2/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/jbd2.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/mm.h>
  #include <linux/freezer.h>
  #include <linux/pagemap.h>
  #include <linux/kthread.h>
  #include <linux/poison.h>
  #include <linux/proc_fs.h>
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  #include <linux/math64.h>
  #include <linux/hash.h>
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/jbd2.h>
  
  #include <asm/uaccess.h>
  #include <asm/page.h>
  
  EXPORT_SYMBOL(jbd2_journal_start);
  EXPORT_SYMBOL(jbd2_journal_restart);
  EXPORT_SYMBOL(jbd2_journal_extend);
  EXPORT_SYMBOL(jbd2_journal_stop);
  EXPORT_SYMBOL(jbd2_journal_lock_updates);
  EXPORT_SYMBOL(jbd2_journal_unlock_updates);
  EXPORT_SYMBOL(jbd2_journal_get_write_access);
  EXPORT_SYMBOL(jbd2_journal_get_create_access);
  EXPORT_SYMBOL(jbd2_journal_get_undo_access);
  EXPORT_SYMBOL(jbd2_journal_set_triggers);
  EXPORT_SYMBOL(jbd2_journal_dirty_metadata);
  EXPORT_SYMBOL(jbd2_journal_release_buffer);
  EXPORT_SYMBOL(jbd2_journal_forget);
  #if 0
  EXPORT_SYMBOL(journal_sync_buffer);
  #endif
  EXPORT_SYMBOL(jbd2_journal_flush);
  EXPORT_SYMBOL(jbd2_journal_revoke);
  
  EXPORT_SYMBOL(jbd2_journal_init_dev);
  EXPORT_SYMBOL(jbd2_journal_init_inode);
  EXPORT_SYMBOL(jbd2_journal_update_format);
  EXPORT_SYMBOL(jbd2_journal_check_used_features);
  EXPORT_SYMBOL(jbd2_journal_check_available_features);
  EXPORT_SYMBOL(jbd2_journal_set_features);
  EXPORT_SYMBOL(jbd2_journal_load);
  EXPORT_SYMBOL(jbd2_journal_destroy);
  EXPORT_SYMBOL(jbd2_journal_abort);
  EXPORT_SYMBOL(jbd2_journal_errno);
  EXPORT_SYMBOL(jbd2_journal_ack_err);
  EXPORT_SYMBOL(jbd2_journal_clear_err);
  EXPORT_SYMBOL(jbd2_log_wait_commit);
  EXPORT_SYMBOL(jbd2_log_start_commit);
  EXPORT_SYMBOL(jbd2_journal_start_commit);
  EXPORT_SYMBOL(jbd2_journal_force_commit_nested);
  EXPORT_SYMBOL(jbd2_journal_wipe);
  EXPORT_SYMBOL(jbd2_journal_blocks_per_page);
  EXPORT_SYMBOL(jbd2_journal_invalidatepage);
  EXPORT_SYMBOL(jbd2_journal_try_to_free_buffers);
  EXPORT_SYMBOL(jbd2_journal_force_commit);
  EXPORT_SYMBOL(jbd2_journal_file_inode);
  EXPORT_SYMBOL(jbd2_journal_init_jbd_inode);
  EXPORT_SYMBOL(jbd2_journal_release_jbd_inode);
  EXPORT_SYMBOL(jbd2_journal_begin_ordered_truncate);
  
  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);
 }
 
 /*
  * kjournald2: 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 kjournald2(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 "kjournald2 starting: pid %d, dev %s, "
                "commit interval %ld seconds\n", current->pid,
                journal->j_devname, journal->j_commit_interval / HZ);
 
         /*
          * And now, wait forever for commit wakeup events.
          */
         spin_lock(&journal->j_state_lock);
 
 loop:
         if (journal->j_flags & JBD2_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);
                 jbd2_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 kjournald2\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 & JBD2_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, "kjournald2 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 jbd2_journal_start_thread(journal_t *journal)
 {
         struct task_struct *t;
 
         t = kthread_run(kjournald2, journal, "kjournald2");
         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 |= JBD2_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);
 }
 
 /*
  * jbd2_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
  * JBD2_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 jbd2_journal_write_metadata_buffer(transaction_t *transaction,
                                   struct journal_head  *jh_in,
                                   struct journal_head **jh_out,
                                   unsigned long 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);
         struct jbd2_buffer_trigger_type *triggers;
         journal_t *journal = transaction->t_journal;
 
         /*
          * The buffer really shouldn't be locked: only the current committing
          * transaction is allowed to write it, so nobody else is allowed
          * to do any IO.
          *
          * akpm: except if we're journalling data, and write() output is
          * also part of a shared mapping, and another thread has
          * decided to launch a writepage() against this buffer.
          */
         J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));
 
         new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
         /* keep subsequent assertions sane */
         new_bh->b_state = 0;
         init_buffer(new_bh, NULL, NULL);
         atomic_set(&new_bh->b_count, 1);
         new_jh = jbd2_journal_add_journal_head(new_bh); /* This sleeps */
 
         /*
          * If a new transaction has already done a buffer copy-out, then
          * we use that version of the data for the commit.
          */
         jbd_lock_bh_state(bh_in);
 repeat:
         if (jh_in->b_frozen_data) {
                 done_copy_out = 1;
                 new_page = virt_to_page(jh_in->b_frozen_data);
                 new_offset = offset_in_page(jh_in->b_frozen_data);
                 triggers = jh_in->b_frozen_triggers;
         } else {
                 new_page = jh2bh(jh_in)->b_page;
                 new_offset = offset_in_page(jh2bh(jh_in)->b_data);
                 triggers = jh_in->b_triggers;
         }
 
         mapped_data = kmap_atomic(new_page, KM_USER0);
         /*
          * Fire any commit trigger.  Do this before checking for escaping,
          * as the trigger may modify the magic offset.  If a copy-out
          * happens afterwards, it will have the correct data in the buffer.
          */
         jbd2_buffer_commit_trigger(jh_in, mapped_data + new_offset,
                                    triggers);
 
         /*
          * Check for escaping
          */
         if (*((__be32 *)(mapped_data + new_offset)) ==
                                 cpu_to_be32(JBD2_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 = jbd2_alloc(bh_in->b_size, GFP_NOFS);
                 if (!tmp) {
                         jbd2_journal_put_journal_head(new_jh);
                         return -ENOMEM;
                 }
                 jbd_lock_bh_state(bh_in);
                 if (jh_in->b_frozen_data) {
                         jbd2_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;
 
                 /*
                  * This isn't strictly necessary, as we're using frozen
                  * data for the escaping, but it keeps consistency with
                  * b_frozen_data usage.
                  */
                 jh_in->b_frozen_triggers = jh_in->b_triggers;
         }
 
         /*
          * 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);
         }
 
         set_bh_page(new_bh, new_page, new_offset);
         new_jh->b_transaction = NULL;
         new_bh->b_size = jh2bh(jh_in)->b_size;
         new_bh->b_bdev = transaction->t_journal->j_dev;
         new_bh->b_blocknr = blocknr;
         set_buffer_mapped(new_bh);
         set_buffer_dirty(new_bh);
 
         *jh_out = new_jh;
 
         /*
          * The to-be-written buffer needs to get moved to the io queue,
          * and the original buffer whose contents we are shadowing or
          * copying is moved to the transaction's shadow queue.
          */
         JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
         spin_lock(&journal->j_list_lock);
         __jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
         spin_unlock(&journal->j_list_lock);
         jbd_unlock_bh_state(bh_in);
 
         JBUFFER_TRACE(new_jh, "file as BJ_IO");
         jbd2_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.
  */
 
 /*
  * __jbd2_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 __jbd2_log_space_left(journal_t *journal)
 {
         int left = journal->j_free;
 
         assert_spin_locked(&journal->j_state_lock);
 
         /*
          * Be pessimistic here about the number of those free blocks which
          * might be required for log descriptor control blocks.
          */
 
 #define MIN_LOG_RESERVED_BLOCKS 32 /* Allow for rounding errors */
 
         left -= MIN_LOG_RESERVED_BLOCKS;
 
         if (left <= 0)
                 return 0;
         left -= (left >> 3);
         return left;
 }
 
 /*
  * Called under j_state_lock.  Returns true if a transaction commit was started.
  */
 int __jbd2_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 jbd2_log_start_commit(journal_t *journal, tid_t tid)
 {
         int ret;
 
         spin_lock(&journal->j_state_lock);
         ret = __jbd2_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 jbd2_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;
                 __jbd2_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);
         jbd2_log_wait_commit(journal, tid);
         return 1;
 }
 
 /*
  * Start a commit of the current running transaction (if any).  Returns true
  * if a transaction is going to be committed (or is currently already
  * committing), and fills its tid in at *ptid
  */
 int jbd2_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;
 
                 __jbd2_log_start_commit(journal, tid);
                 /* There's a running transaction and we've just made sure
                  * it's commit has been scheduled. */
                 if (ptid)
                         *ptid = tid;
                 ret = 1;
         } else if (journal->j_committing_transaction) {
                 /*
                  * If ext3_write_super() recently started a commit, then we
                  * have to wait for completion of that transaction
                  */
                 if (ptid)
                         *ptid = journal->j_committing_transaction->t_tid;
                 ret = 1;
         }
         spin_unlock(&journal->j_state_lock);
         return ret;
 }
 
 /*
  * Wait for a specified commit to complete.
  * The caller may not hold the journal lock.
  */
 int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
 {
         int err = 0;
 
 #ifdef CONFIG_JBD2_DEBUG
         spin_lock(&journal->j_state_lock);
         if (!tid_geq(journal->j_commit_request, tid)) {
                 printk(KERN_EMERG
                        "%s: error: j_commit_request=%d, tid=%d\n",
                        __func__, journal->j_commit_request, tid);
         }
         spin_unlock(&journal->j_state_lock);
 #endif
         spin_lock(&journal->j_state_lock);
         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 jbd2_journal_next_log_block(journal_t *journal, unsigned long 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 jbd2_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 jbd2_journal_bmap(journal_t *journal, unsigned long blocknr,
                  unsigned long long *retp)
 {
         int err = 0;
         unsigned long long ret;
 
         if (journal->j_inode) {
                 ret = bmap(journal->j_inode, blocknr);
                 if (ret)
                         *retp = ret;
                 else {
                         printk(KERN_ALERT "%s: journal block not found "
                                         "at offset %lu on %s\n",
                                __func__, blocknr, journal->j_devname);
                         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 jbd2_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 *jbd2_journal_get_descriptor_buffer(journal_t *journal)
 {
         struct buffer_head *bh;
         unsigned long long blocknr;
         int err;
 
         err = jbd2_journal_next_log_block(journal, &blocknr);
 
         if (err)
                 return NULL;
 
         bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
         if (!bh)
                 return NULL;
         lock_buffer(bh);
         memset(bh->b_data, 0, journal->j_blocksize);
         set_buffer_uptodate(bh);
         unlock_buffer(bh);
         BUFFER_TRACE(bh, "return this buffer");
         return jbd2_journal_add_journal_head(bh);
 }
 
 struct jbd2_stats_proc_session {
         journal_t *journal;
         struct transaction_stats_s *stats;
         int start;
         int max;
 };
 
 static void *jbd2_history_skip_empty(struct jbd2_stats_proc_session *s,
                                         struct transaction_stats_s *ts,
                                         int first)
 {
         if (ts == s->stats + s->max)
                 ts = s->stats;
         if (!first && ts == s->stats + s->start)
                 return NULL;
         while (ts->ts_type == 0) {
                 ts++;
                 if (ts == s->stats + s->max)
                         ts = s->stats;
                 if (ts == s->stats + s->start)
                         return NULL;
         }
         return ts;
 
 }
 
 static void *jbd2_seq_history_start(struct seq_file *seq, loff_t *pos)
 {
         struct jbd2_stats_proc_session *s = seq->private;
         struct transaction_stats_s *ts;
         int l = *pos;
 
         if (l == 0)
                 return SEQ_START_TOKEN;
         ts = jbd2_history_skip_empty(s, s->stats + s->start, 1);
         if (!ts)
                 return NULL;
         l--;
         while (l) {
                 ts = jbd2_history_skip_empty(s, ++ts, 0);
                 if (!ts)
                         break;
                 l--;
         }
         return ts;
 }
 
 static void *jbd2_seq_history_next(struct seq_file *seq, void *v, loff_t *pos)
 {
         struct jbd2_stats_proc_session *s = seq->private;
         struct transaction_stats_s *ts = v;
 
         ++*pos;
         if (v == SEQ_START_TOKEN)
                 return jbd2_history_skip_empty(s, s->stats + s->start, 1);
         else
                 return jbd2_history_skip_empty(s, ++ts, 0);
 }
 
 static int jbd2_seq_history_show(struct seq_file *seq, void *v)
 {
         struct transaction_stats_s *ts = v;
         if (v == SEQ_START_TOKEN) {
                 seq_printf(seq, "%-4s %-5s %-5s %-5s %-5s %-5s %-5s %-6s %-5s "
                                 "%-5s %-5s %-5s %-5s %-5s\n", "R/C", "tid",
                                 "wait", "run", "lock", "flush", "log", "hndls",
                                 "block", "inlog", "ctime", "write", "drop",
                                 "close");
                 return 0;
         }
         if (ts->ts_type == JBD2_STATS_RUN)
                 seq_printf(seq, "%-4s %-5lu %-5u %-5u %-5u %-5u %-5u "
                                 "%-6lu %-5lu %-5lu\n", "R", ts->ts_tid,
                                 jiffies_to_msecs(ts->u.run.rs_wait),
                                 jiffies_to_msecs(ts->u.run.rs_running),
                                 jiffies_to_msecs(ts->u.run.rs_locked),
                                 jiffies_to_msecs(ts->u.run.rs_flushing),
                                 jiffies_to_msecs(ts->u.run.rs_logging),
                                 ts->u.run.rs_handle_count,
                                 ts->u.run.rs_blocks,
                                 ts->u.run.rs_blocks_logged);
         else if (ts->ts_type == JBD2_STATS_CHECKPOINT)
                 seq_printf(seq, "%-4s %-5lu %48s %-5u %-5lu %-5lu %-5lu\n",
                                 "C", ts->ts_tid, " ",
                                 jiffies_to_msecs(ts->u.chp.cs_chp_time),
                                 ts->u.chp.cs_written, ts->u.chp.cs_dropped,
                                 ts->u.chp.cs_forced_to_close);
         else
                 J_ASSERT(0);
         return 0;
 }
 
 static void jbd2_seq_history_stop(struct seq_file *seq, void *v)
 {
 }
 
 static struct seq_operations jbd2_seq_history_ops = {
         .start  = jbd2_seq_history_start,
         .next   = jbd2_seq_history_next,
         .stop   = jbd2_seq_history_stop,
         .show   = jbd2_seq_history_show,
 };
 
 static int jbd2_seq_history_open(struct inode *inode, struct file *file)
 {
         journal_t *journal = PDE(inode)->data;
         struct jbd2_stats_proc_session *s;
         int rc, size;
 
         s = kmalloc(sizeof(*s), GFP_KERNEL);
         if (s == NULL)
                 return -ENOMEM;
         size = sizeof(struct transaction_stats_s) * journal->j_history_max;
         s->stats = kmalloc(size, GFP_KERNEL);
         if (s->stats == NULL) {
                 kfree(s);
                 return -ENOMEM;
         }
         spin_lock(&journal->j_history_lock);
         memcpy(s->stats, journal->j_history, size);
         s->max = journal->j_history_max;
         s->start = journal->j_history_cur % s->max;
         spin_unlock(&journal->j_history_lock);
 
         rc = seq_open(file, &jbd2_seq_history_ops);
         if (rc == 0) {
                 struct seq_file *m = file->private_data;
                 m->private = s;
         } else {
                 kfree(s->stats);
                 kfree(s);
         }
         return rc;
 
 }
 
 static int jbd2_seq_history_release(struct inode *inode, struct file *file)
 {
         struct seq_file *seq = file->private_data;
         struct jbd2_stats_proc_session *s = seq->private;
 
         kfree(s->stats);
         kfree(s);
         return seq_release(inode, file);
 }
 
 static struct file_operations jbd2_seq_history_fops = {
         .owner          = THIS_MODULE,
         .open           = jbd2_seq_history_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
         .release        = jbd2_seq_history_release,
 };
 
 static void *jbd2_seq_info_start(struct seq_file *seq, loff_t *pos)
 {
         return *pos ? NULL : SEQ_START_TOKEN;
 }
 
 static void *jbd2_seq_info_next(struct seq_file *seq, void *v, loff_t *pos)
 {
         return NULL;
 }
 
 static int jbd2_seq_info_show(struct seq_file *seq, void *v)
 {
         struct jbd2_stats_proc_session *s = seq->private;
 
         if (v != SEQ_START_TOKEN)
                 return 0;
         seq_printf(seq, "%lu transaction, each upto %u blocks\n",
                         s->stats->ts_tid,
                         s->journal->j_max_transaction_buffers);
         if (s->stats->ts_tid == 0)
                 return 0;
         seq_printf(seq, "average: \n  %ums waiting for transaction\n",
             jiffies_to_msecs(s->stats->u.run.rs_wait / s->stats->ts_tid));
         seq_printf(seq, "  %ums running transaction\n",
             jiffies_to_msecs(s->stats->u.run.rs_running / s->stats->ts_tid));
         seq_printf(seq, "  %ums transaction was being locked\n",
             jiffies_to_msecs(s->stats->u.run.rs_locked / s->stats->ts_tid));
         seq_printf(seq, "  %ums flushing data (in ordered mode)\n",
             jiffies_to_msecs(s->stats->u.run.rs_flushing / s->stats->ts_tid));
         seq_printf(seq, "  %ums logging transaction\n",
             jiffies_to_msecs(s->stats->u.run.rs_logging / s->stats->ts_tid));
         seq_printf(seq, "  %lluus average transaction commit time\n",
                    div_u64(s->journal->j_average_commit_time, 1000));
         seq_printf(seq, "  %lu handles per transaction\n",
             s->stats->u.run.rs_handle_count / s->stats->ts_tid);
         seq_printf(seq, "  %lu blocks per transaction\n",
             s->stats->u.run.rs_blocks / s->stats->ts_tid);
         seq_printf(seq, "  %lu logged blocks per transaction\n",
             s->stats->u.run.rs_blocks_logged / s->stats->ts_tid);
         return 0;
 }
 
 static void jbd2_seq_info_stop(struct seq_file *seq, void *v)
 {
 }
 
 static struct seq_operations jbd2_seq_info_ops = {
         .start  = jbd2_seq_info_start,
         .next   = jbd2_seq_info_next,
         .stop   = jbd2_seq_info_stop,
         .show   = jbd2_seq_info_show,
 };
 
 static int jbd2_seq_info_open(struct inode *inode, struct file *file)
 {
         journal_t *journal = PDE(inode)->data;
         struct jbd2_stats_proc_session *s;
         int rc, size;
 
         s = kmalloc(sizeof(*s), GFP_KERNEL);
         if (s == NULL)
                 return -ENOMEM;
         size = sizeof(struct transaction_stats_s);
         s->stats = kmalloc(size, GFP_KERNEL);
         if (s->stats == NULL) {
                 kfree(s);
                 return -ENOMEM;
         }
         spin_lock(&journal->j_history_lock);
         memcpy(s->stats, &journal->j_stats, size);
         s->journal = journal;
         spin_unlock(&journal->j_history_lock);
 
         rc = seq_open(file, &jbd2_seq_info_ops);
         if (rc == 0) {
                 struct seq_file *m = file->private_data;
                 m->private = s;
         } else {
                 kfree(s->stats);
                 kfree(s);
         }
         return rc;
 
 }
 
 static int jbd2_seq_info_release(struct inode *inode, struct file *file)
 {
         struct seq_file *seq = file->private_data;
         struct jbd2_stats_proc_session *s = seq->private;
         kfree(s->stats);
         kfree(s);
         return seq_release(inode, file);
 }
 
 static struct file_operations jbd2_seq_info_fops = {
         .owner          = THIS_MODULE,
         .open           = jbd2_seq_info_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
         .release        = jbd2_seq_info_release,
 };
 
 static struct proc_dir_entry *proc_jbd2_stats;
 
 static void jbd2_stats_proc_init(journal_t *journal)
 {
         journal->j_proc_entry = proc_mkdir(journal->j_devname, proc_jbd2_stats);
         if (journal->j_proc_entry) {
                 proc_create_data("history", S_IRUGO, journal->j_proc_entry,
                                  &jbd2_seq_history_fops, journal);
                 proc_create_data("info", S_IRUGO, journal->j_proc_entry,
                                  &jbd2_seq_info_fops, journal);
         }
 }
 
 static void jbd2_stats_proc_exit(journal_t *journal)
 {
         remove_proc_entry("info", journal->j_proc_entry);
         remove_proc_entry("history", journal->j_proc_entry);
         remove_proc_entry(journal->j_devname, proc_jbd2_stats);
 }
 
 static void journal_init_stats(journal_t *journal)
 {
         int size;
 
         if (!proc_jbd2_stats)
                 return;
 
         journal->j_history_max = 100;
         size = sizeof(struct transaction_stats_s) * journal->j_history_max;
         journal->j_history = kzalloc(size, GFP_KERNEL);
         if (!journal->j_history) {
                 journal->j_history_max = 0;
                 return;
         }
         spin_lock_init(&journal->j_history_lock);
 }
 
 /*
  * 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|__GFP_NOFAIL);
         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 * JBD2_DEFAULT_MAX_COMMIT_AGE);
         journal->j_min_batch_time = 0;
         journal->j_max_batch_time = 15000; /* 15ms */
 
         /* The journal is marked for error until we succeed with recovery! */
         journal->j_flags = JBD2_ABORT;
 
         /* Set up a default-sized revoke table for the new mount. */
         err = jbd2_journal_init_revoke(journal, JOURNAL_REVOKE_DEFAULT_HASH);
         if (err) {
                 kfree(journal);
                 goto fail;
         }
 
         journal_init_stats(journal);
 
         return journal;
 fail:
         return NULL;
 }
 
 /* jbd2_journal_init_dev and jbd2_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 * jbd2_journal_init_dev() - creates and 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 *
  *
  *  jbd2_journal_init_dev creates a journal which maps a fixed contiguous
  *  range of blocks on an arbitrary block device.
  *
  */
 journal_t * jbd2_journal_init_dev(struct block_device *bdev,
                         struct block_device *fs_dev,
                         unsigned long long start, int len, int blocksize)
 {
         journal_t *journal = journal_init_common();
         struct buffer_head *bh;
         char *p;
         int n;
 
         if (!journal)
                 return NULL;
 
         /* journal descriptor can store up to n blocks -bzzz */
         journal->j_blocksize = blocksize;
         jbd2_stats_proc_init(journal);
         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",
                         __func__);
                 goto out_err;
         }
         journal->j_dev = bdev;
         journal->j_fs_dev = fs_dev;
         journal->j_blk_offset = start;
         journal->j_maxlen = len;
         bdevname(journal->j_dev, journal->j_devname);
         p = journal->j_devname;
         while ((p = strchr(p, '/')))
                 *p = '!';
 
         bh = __getblk(journal->j_dev, start, journal->j_blocksize);
         if (!bh) {
                 printk(KERN_ERR
                        "%s: Cannot get buffer for journal superblock\n",
                        __func__);
                 goto out_err;
         }
         journal->j_sb_buffer = bh;
         journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
         return journal;
 out_err:
         jbd2_stats_proc_exit(journal);
         kfree(journal);
         return NULL;
 }
 
 /**
  *  journal_t * jbd2_journal_init_inode () - creates a journal which maps to a inode.
  *  @inode: An inode to create the journal in
  *
  * jbd2_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 * jbd2_journal_init_inode (struct inode *inode)
 {
         struct buffer_head *bh;
         journal_t *journal = journal_init_common();
         char *p;
         int err;
         int n;
         unsigned long long blocknr;
 
         if (!journal)
                 return NULL;
 
         journal->j_dev = journal->j_fs_dev = inode->i_sb->s_bdev;
         journal->j_inode = inode;
         bdevname(journal->j_dev, journal->j_devname);
         p = journal->j_devname;
         while ((p = strchr(p, '/')))
                 *p = '!';
         p = journal->j_devname + strlen(journal->j_devname);
         sprintf(p, ":%lu", journal->j_inode->i_ino);
         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;
         jbd2_stats_proc_init(journal);
 
         /* 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",
                         __func__);
                 goto out_err;
         }
 
         err = jbd2_journal_bmap(journal, 0, &blocknr);
         /* If that failed, give up */
         if (err) {
                 printk(KERN_ERR "%s: Cannnot locate journal superblock\n",
                        __func__);
                 goto out_err;
         }
 
         bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
         if (!bh) {
                 printk(KERN_ERR
                        "%s: Cannot get buffer for journal superblock\n",
                        __func__);
                 goto out_err;
         }
         journal->j_sb_buffer = bh;
         journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
         return journal;
 out_err:
         jbd2_stats_proc_exit(journal);
         kfree(journal);
         return NULL;
 }
 
 /*
  * If the journal init or create aborts, we need to mark the journal
  * superblock as being NULL to prevent the journal destroy from writing
  * back a bogus superblock.
  */
 static void journal_fail_superblock (journal_t *journal)
 {
         struct buffer_head *bh = journal->j_sb_buffer;
         brelse(bh);
         journal->j_sb_buffer = NULL;
 }
 
 /*
  * Given a journal_t structure, initialise the various fields for
  * startup of a new journaling session.  We use this both when creating
  * a journal, and after recovering an old journal to reset it for
  * subsequent use.
  */
 
 static int journal_reset(journal_t *journal)
 {
         journal_superblock_t *sb = journal->j_superblock;
         unsigned long long first, last;
 
         first = be32_to_cpu(sb->s_first);
         last = be32_to_cpu(sb->s_maxlen);
         if (first + JBD2_MIN_JOURNAL_BLOCKS > last + 1) {
                 printk(KERN_ERR "JBD: Journal too short (blocks %llu-%llu).\n",
                        first, last);
                 journal_fail_superblock(journal);
                 return -EINVAL;
         }
 
         journal->j_first = first;
         journal->j_last = last;
 
         journal->j_head = first;
         journal->j_tail = first;
         journal->j_free = last - first;
 
         journal->j_tail_sequence = journal->j_transaction_sequence;
         journal->j_commit_sequence = journal->j_transaction_sequence - 1;
         journal->j_commit_request = journal->j_commit_sequence;
 
         journal->j_max_transaction_buffers = journal->j_maxlen / 4;
 
         /* Add the dynamic fields and write it to disk. */
         jbd2_journal_update_superblock(journal, 1);
         return jbd2_journal_start_thread(journal);
 }
 
 /**
  * void jbd2_journal_update_superblock() - Update journal sb on disk.
  * @journal: The journal to update.
  * @wait: Set to '' 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 jbd2_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 JBD2_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;
         }
 
         if (buffer_write_io_error(bh)) {
                 /*
                  * Oh, dear.  A previous attempt to write the journal
                  * superblock failed.  This could happen because the
                  * USB device was yanked out.  Or it could happen to
                  * be a transient write error and maybe the block will
                  * be remapped.  Nothing we can do but to retry the
                  * write and hope for the best.
                  */
                 printk(KERN_ERR "JBD2: previous I/O error detected "
                        "for journal superblock update for %s.\n",
                        journal->j_devname);
                 clear_buffer_write_io_error(bh);
                 set_buffer_uptodate(bh);
         }
 
         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);
                 if (buffer_write_io_error(bh)) {
                         printk(KERN_ERR "JBD2: I/O error detected "
                                "when updating journal superblock for %s.\n",
                                journal->j_devname);
                         clear_buffer_write_io_error(bh);
                         set_buffer_uptodate(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 &= ~JBD2_FLUSHED;
         else
                 journal->j_flags |= JBD2_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(JBD2_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 JBD2_SUPERBLOCK_V1:
                 journal->j_format_version = 1;
                 break;
         case JBD2_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 jbd2_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 jbd2_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(JBD2_KNOWN_ROCOMPAT_FEATURES)) ||
                     (sb->s_feature_incompat &
                      ~cpu_to_be32(JBD2_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 (jbd2_journal_recover(journal))
                 goto recovery_error;
 
         if (journal->j_failed_commit) {
                 printk(KERN_ERR "JBD2: journal transaction %u on %s "
                        "is corrupt.\n", journal->j_failed_commit,
                        journal->j_devname);
                 return -EIO;
         }
 
         /* 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 &= ~JBD2_ABORT;
         journal->j_flags |= JBD2_LOADED;
         return 0;
 
 recovery_error:
         printk (KERN_WARNING "JBD: recovery failed\n");
         return -EIO;
 }
 
 /**
  * void jbd2_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.
  * Return <0 if we couldn't clean up the journal.
  */
 int jbd2_journal_destroy(journal_t *journal)
 {
         int err = 0;
 
         /* Wait for the commit thread to wake up and die. */
         journal_kill_thread(journal);
 
         /* Force a final log commit */
         if (journal->j_running_transaction)
                 jbd2_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);
                 mutex_lock(&journal->j_checkpoint_mutex);
                 jbd2_log_do_checkpoint(journal);
                 mutex_unlock(&journal->j_checkpoint_mutex);
                 spin_lock(&journal->j_list_lock);
         }
 
         J_ASSERT(journal->j_running_transaction == NULL);
         J_ASSERT(journal->j_committing_transaction == NULL);
         J_ASSERT(journal->j_checkpoint_transactions == NULL);
         spin_unlock(&journal->j_list_lock);
 
         if (journal->j_sb_buffer) {
                 if (!is_journal_aborted(journal)) {
                         /* We can now mark the journal as empty. */
                         journal->j_tail = 0;
                         journal->j_tail_sequence =
                                 ++journal->j_transaction_sequence;
                         jbd2_journal_update_superblock(journal, 1);
                 } else {
                         err = -EIO;
                 }
                 brelse(journal->j_sb_buffer);
         }
 
         if (journal->j_proc_entry)
                 jbd2_stats_proc_exit(journal);
         if (journal->j_inode)
                 iput(journal->j_inode);
         if (journal->j_revoke)
                 jbd2_journal_destroy_revoke(journal);
         kfree(journal->j_wbuf);
         kfree(journal);
 
         return err;
 }
 
 
 /**
  *int jbd2_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 jbd2_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 jbd2_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 jbd2_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   & JBD2_KNOWN_COMPAT_FEATURES) == compat &&
             (ro       & JBD2_KNOWN_ROCOMPAT_FEATURES) == ro &&
             (incompat & JBD2_KNOWN_INCOMPAT_FEATURES) == incompat)
                 return 1;
 
         return 0;
 }
 
 /**
  * int jbd2_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 jbd2_journal_set_features (journal_t *journal, unsigned long compat,
                           unsigned long ro, unsigned long incompat)
 {
         journal_superblock_t *sb;
 
         if (jbd2_journal_check_used_features(journal, compat, ro, incompat))
                 return 1;
 
         if (!jbd2_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;
 }
 
 /*
  * jbd2_journal_clear_features () - Clear 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
  *
  * Clear a given journal feature as present on the
  * superblock.
  */
 void jbd2_journal_clear_features(journal_t *journal, unsigned long compat,
                                 unsigned long ro, unsigned long incompat)
 {
         journal_superblock_t *sb;
 
         jbd_debug(1, "Clear 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);
 }
 EXPORT_SYMBOL(jbd2_journal_clear_features);
 
 /**
  * int jbd2_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 jbd2_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 JBD2_SUPERBLOCK_V2:
                 return 0;
         case JBD2_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(JBD2_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 jbd2_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 jbd2_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;
                 __jbd2_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);
                 jbd2_log_wait_commit(journal, tid);
         } else {
                 spin_unlock(&journal->j_state_lock);
         }
 
         /* ...and flush everything in the log out to disk. */
         spin_lock(&journal->j_list_lock);
         while (!err && journal->j_checkpoint_transactions != NULL) {
                 spin_unlock(&journal->j_list_lock);
                 mutex_lock(&journal->j_checkpoint_mutex);
                 err = jbd2_log_do_checkpoint(journal);
                 mutex_unlock(&journal->j_checkpoint_mutex);
                 spin_lock(&journal->j_list_lock);
         }
         spin_unlock(&journal->j_list_lock);
 
         if (is_journal_aborted(journal))
                 return -EIO;
 
         jbd2_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);
         jbd2_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 0;
 }
 
 /**
  * int jbd2_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 jbd2_journal_load().
  *
  * If 'write' is non-zero, then we wipe out the journal on disk; otherwise
  * we merely suppress recovery.
  */
 
 int jbd2_journal_wipe(journal_t *journal, int write)
 {
         journal_superblock_t *sb;
         int err = 0;
 
         J_ASSERT (!(journal->j_flags & JBD2_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 = jbd2_journal_skip_recovery(journal);
         if (write)
                 jbd2_journal_update_superblock(journal, 1);
 
  no_recovery:
         return err;
 }
 
 /*
  * Journal abort has very specific semantics, which we describe
  * for journal abort.
  *
  * Two internal functions, which provide abort to the 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 __jbd2_journal_abort_hard(journal_t *journal)
 {
         transaction_t *transaction;
 
         if (journal->j_flags & JBD2_ABORT)
                 return;
 
         printk(KERN_ERR "Aborting journal on device %s.\n",
                journal->j_devname);
 
         spin_lock(&journal->j_state_lock);
         journal->j_flags |= JBD2_ABORT;
         transaction = journal->j_running_transaction;
         if (transaction)
                 __jbd2_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 & JBD2_ABORT)
                 return;
 
         if (!journal->j_errno)
                 journal->j_errno = errno;
 
         __jbd2_journal_abort_hard(journal);
 
         if (errno)
                 jbd2_journal_update_superblock(journal, 1);
 }
 
 /**
  * void jbd2_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 jbd2_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
  * jbd2_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 jbd2_journal_stop, which will receive the -EIO error.
  *
  * Finally, the jbd2_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 jbd2_journal_abort(journal_t *journal, int errno)
 {
         __journal_abort_soft(journal, errno);
 }
 
 /**
  * int jbd2_journal_errno () - returns the journal's error state.
  * @journal: journal to examine.
  *
  * This is the errno number set with jbd2_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 jbd2_journal_errno(journal_t *journal)
 {
         int err;
 
         spin_lock(&journal->j_state_lock);
         if (journal->j_flags & JBD2_ABORT)
                 err = -EROFS;
         else
                 err = journal->j_errno;
         spin_unlock(&journal->j_state_lock);
         return err;
 }
 
 /**
  * int jbd2_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 jbd2_journal_clear_err(journal_t *journal)
 {
         int err = 0;
 
         spin_lock(&journal->j_state_lock);
         if (journal->j_flags & JBD2_ABORT)
                 err = -EROFS;
         else
                 journal->j_errno = 0;
         spin_unlock(&journal->j_state_lock);
         return err;
 }
 
 /**
  * void jbd2_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 jbd2_journal_ack_err(journal_t *journal)
 {
         spin_lock(&journal->j_state_lock);
         if (journal->j_errno)
                 journal->j_flags |= JBD2_ACK_ERR;
         spin_unlock(&journal->j_state_lock);
 }
 
 int jbd2_journal_blocks_per_page(struct inode *inode)
 {
         return 1 << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
 }
 
 /*
  * helper functions to deal with 32 or 64bit block numbers.
  */
 size_t journal_tag_bytes(journal_t *journal)
 {
         if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
                 return JBD2_TAG_SIZE64;
         else
                 return JBD2_TAG_SIZE32;
 }
 
 /*
  * Journal_head storage management
  */
 static struct kmem_cache *jbd2_journal_head_cache;
 #ifdef CONFIG_JBD2_DEBUG
 static atomic_t nr_journal_heads = ATOMIC_INIT(0);
 #endif
 
 static int journal_init_jbd2_journal_head_cache(void)
 {
         int retval;
 
         J_ASSERT(jbd2_journal_head_cache == NULL);
         jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
                                 sizeof(struct journal_head),
                                 0,              /* offset */
                                 SLAB_TEMPORARY, /* flags */
                                 NULL);          /* ctor */
         retval = 0;
         if (!jbd2_journal_head_cache) {
                 retval = -ENOMEM;
                 printk(KERN_EMERG "JBD: no memory for journal_head cache\n");
         }
         return retval;
 }
 
 static void jbd2_journal_destroy_jbd2_journal_head_cache(void)
 {
         if (jbd2_journal_head_cache) {
                 kmem_cache_destroy(jbd2_journal_head_cache);
                 jbd2_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_JBD2_DEBUG
         atomic_inc(&nr_journal_heads);
 #endif
         ret = kmem_cache_alloc(jbd2_journal_head_cache, GFP_NOFS);
         if (!ret) {
                 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",
                                __func__);
                         last_warning = jiffies;
                 }
                 while (!ret) {
                         yield();
                         ret = kmem_cache_alloc(jbd2_journal_head_cache, GFP_NOFS);
                 }
         }
         return ret;
 }
 
 static void journal_free_journal_head(struct journal_head *jh)
 {
 #ifdef CONFIG_JBD2_DEBUG
         atomic_dec(&nr_journal_heads);
         memset(jh, JBD2_POISON_FREE, sizeof(*jh));
 #endif
         kmem_cache_free(jbd2_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 jbd2_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, jbd2_journal_add_journal_head elevates the
  * journal_head's b_jcount refcount by one.  The caller must call
  * jbd2_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 = jbd2_journal_add_journal_head(bh);
  *      ...
  *      jh->b_transaction = xxx;
  *      jbd2_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 *jbd2_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 *jbd2_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",
                                                 __func__);
                                 jbd2_free(jh->b_frozen_data, bh->b_size);
                         }
                         if (jh->b_committed_data) {
                                 printk(KERN_WARNING "%s: freeing "
                                                 "b_committed_data\n",
                                                 __func__);
                                 jbd2_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");
                 }
         }
 }
 
 /*
  * jbd2_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 jbd2_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 jbd2_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 jbd2_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);
 }
 
 /*
  * Initialize jbd inode head
  */
 void jbd2_journal_init_jbd_inode(struct jbd2_inode *jinode, struct inode *inode)
 {
         jinode->i_transaction = NULL;
         jinode->i_next_transaction = NULL;
         jinode->i_vfs_inode = inode;
         jinode->i_flags = 0;
         INIT_LIST_HEAD(&jinode->i_list);
 }
 
 /*
  * Function to be called before we start removing inode from memory (i.e.,
  * clear_inode() is a fine place to be called from). It removes inode from
  * transaction's lists.
  */
 void jbd2_journal_release_jbd_inode(journal_t *journal,
                                     struct jbd2_inode *jinode)
 {
         int writeout = 0;
 
         if (!journal)
                 return;
 restart:
         spin_lock(&journal->j_list_lock);
         /* Is commit writing out inode - we have to wait */
         if (jinode->i_flags & JI_COMMIT_RUNNING) {
                 wait_queue_head_t *wq;
                 DEFINE_WAIT_BIT(wait, &jinode->i_flags, __JI_COMMIT_RUNNING);
                 wq = bit_waitqueue(&jinode->i_flags, __JI_COMMIT_RUNNING);
                 prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
                 spin_unlock(&journal->j_list_lock);
                 schedule();
                 finish_wait(wq, &wait.wait);
                 goto restart;
         }
 
         /* Do we need to wait for data writeback? */
         if (journal->j_committing_transaction == jinode->i_transaction)
                 writeout = 1;
         if (jinode->i_transaction) {
                 list_del(&jinode->i_list);
                 jinode->i_transaction = NULL;
         }
         spin_unlock(&journal->j_list_lock);
 }
 
 /*
  * debugfs tunables
  */
 #ifdef CONFIG_JBD2_DEBUG
 u8 jbd2_journal_enable_debug __read_mostly;
 EXPORT_SYMBOL(jbd2_journal_enable_debug);
 
 #define JBD2_DEBUG_NAME "jbd2-debug"
 
 static struct dentry *jbd2_debugfs_dir;
 static struct dentry *jbd2_debug;
 
 static void __init jbd2_create_debugfs_entry(void)
 {
         jbd2_debugfs_dir = debugfs_create_dir("jbd2", NULL);
         if (jbd2_debugfs_dir)
                 jbd2_debug = debugfs_create_u8(JBD2_DEBUG_NAME, S_IRUGO,
                                                jbd2_debugfs_dir,
                                                &jbd2_journal_enable_debug);
 }
 
 static void __exit jbd2_remove_debugfs_entry(void)
 {
         debugfs_remove(jbd2_debug);
         debugfs_remove(jbd2_debugfs_dir);
 }
 
 #else
 
 static void __init jbd2_create_debugfs_entry(void)
 {
 }
 
 static void __exit jbd2_remove_debugfs_entry(void)
 {
 }
 
 #endif
 
 #ifdef CONFIG_PROC_FS
 
 #define JBD2_STATS_PROC_NAME "fs/jbd2"
 
 static void __init jbd2_create_jbd_stats_proc_entry(void)
 {
         proc_jbd2_stats = proc_mkdir(JBD2_STATS_PROC_NAME, NULL);
 }
 
 static void __exit jbd2_remove_jbd_stats_proc_entry(void)
 {
         if (proc_jbd2_stats)
                 remove_proc_entry(JBD2_STATS_PROC_NAME, NULL);
 }
 
 #else
 
 #define jbd2_create_jbd_stats_proc_entry() do {} while (0)
 #define jbd2_remove_jbd_stats_proc_entry() do {} while (0)
 
 #endif
 
 struct kmem_cache *jbd2_handle_cache;
 
 static int __init journal_init_handle_cache(void)
 {
         jbd2_handle_cache = kmem_cache_create("jbd2_journal_handle",
                                 sizeof(handle_t),
                                 0,              /* offset */
                                 SLAB_TEMPORARY, /* flags */
                                 NULL);          /* ctor */
         if (jbd2_handle_cache == NULL) {
                 printk(KERN_EMERG "JBD: failed to create handle cache\n");
                 return -ENOMEM;
         }
         return 0;
 }
 
 static void jbd2_journal_destroy_handle_cache(void)
 {
         if (jbd2_handle_cache)
                 kmem_cache_destroy(jbd2_handle_cache);
 }
 
 /*
  * Module startup and shutdown
  */
 
 static int __init journal_init_caches(void)
 {
         int ret;
 
         ret = jbd2_journal_init_revoke_caches();
         if (ret == 0)
                 ret = journal_init_jbd2_journal_head_cache();
         if (ret == 0)
                 ret = journal_init_handle_cache();
         return ret;
 }
 
 static void jbd2_journal_destroy_caches(void)
 {
         jbd2_journal_destroy_revoke_caches();
         jbd2_journal_destroy_jbd2_journal_head_cache();
         jbd2_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) {
                 jbd2_create_debugfs_entry();
                 jbd2_create_jbd_stats_proc_entry();
         } else {
                 jbd2_journal_destroy_caches();
         }
         return ret;
 }
 
 static void __exit journal_exit(void)
 {
 #ifdef CONFIG_JBD2_DEBUG
         int n = atomic_read(&nr_journal_heads);
         if (n)
                 printk(KERN_EMERG "JBD: leaked %d journal_heads!\n", n);
 #endif
         jbd2_remove_debugfs_entry();
         jbd2_remove_jbd_stats_proc_entry();
         jbd2_journal_destroy_caches();
 }
 
 /* 
  * jbd2_dev_to_name is a utility function used by the jbd2 and ext4 
  * tracing infrastructure to map a dev_t to a device name.
  *
  * The caller should use rcu_read_lock() in order to make sure the
  * device name stays valid until its done with it.  We use
  * rcu_read_lock() as well to make sure we're safe in case the caller
  * gets sloppy, and because rcu_read_lock() is cheap and can be safely
  * nested.
  */
 struct devname_cache {
         struct rcu_head rcu;
         dev_t           device;
         char            devname[BDEVNAME_SIZE];
 };
 #define CACHE_SIZE_BITS 6
 static struct devname_cache *devcache[1 << CACHE_SIZE_BITS];
 static DEFINE_SPINLOCK(devname_cache_lock);
 
 static void free_devcache(struct rcu_head *rcu)
 {
         kfree(rcu);
 }
 
 const char *jbd2_dev_to_name(dev_t device)
 {
         int     i = hash_32(device, CACHE_SIZE_BITS);
         char    *ret;
         struct block_device *bd;
         static struct devname_cache *new_dev;
 
         rcu_read_lock();
         if (devcache[i] && devcache[i]->device == device) {
                 ret = devcache[i]->devname;
                 rcu_read_unlock();
                 return ret;
         }
         rcu_read_unlock();
 
         new_dev = kmalloc(sizeof(struct devname_cache), GFP_KERNEL);
         if (!new_dev)
                 return "NODEV-ALLOCFAILURE"; /* Something non-NULL */
         spin_lock(&devname_cache_lock);
         if (devcache[i]) {
                 if (devcache[i]->device == device) {
                         kfree(new_dev);
                         ret = devcache[i]->devname;
                         spin_unlock(&devname_cache_lock);
                         return ret;
                 }
                 call_rcu(&devcache[i]->rcu, free_devcache);
         }
         devcache[i] = new_dev;
         devcache[i]->device = device;
         bd = bdget(device);
         if (bd) {
                 bdevname(bd, devcache[i]->devname);
                 bdput(bd);
         } else
                 __bdevname(device, devcache[i]->devname);
         ret = devcache[i]->devname;
         spin_unlock(&devname_cache_lock);
         return ret;
 }
 EXPORT_SYMBOL(jbd2_dev_to_name);
 
 MODULE_LICENSE("GPL");
 module_init(journal_init);
 module_exit(journal_exit);