text: /*
   * 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/smp_lock.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 <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_dirty_data);
  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_create);
  EXPORT_SYMBOL(jbd2_journal_load);
  EXPORT_SYMBOL(jbd2_journal_destroy);
  EXPORT_SYMBOL(jbd2_journal_update_superblock);
  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_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);
  
  static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
  static void __journal_abort_soft (journal_t *journal, int errno);
  static int jbd2_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);
  }
  
  /*
   * 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.  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 & 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 void jbd2_journal_start_thread(journal_t *journal)
  {
  	kthread_run(kjournald2, journal, "kjournald2");
  	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 |= 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 == 0);
  		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);
  
  	/*
  	 * 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(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_slab_alloc(bh_in->b_size, GFP_NOFS);
  		jbd_lock_bh_state(bh_in);
  		if (jh_in->b_frozen_data) {
  			jbd2_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 = jbd2_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");
  	jbd2_journal_file_buffer(jh_in, transaction, BJ_Shadow);
  	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 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 was started, 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;
  
  		ret = __jbd2_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 jbd2_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 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 {
  			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 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);
  	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);
  }
  
  /*
   * 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 = 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;
  	}
  	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 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 *
   *
   *  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;
  	int n;
  
  	if (!journal)
  		return NULL;
  
  	/* journal descriptor can store up to n blocks -bzzz */
  	journal->j_blocksize = blocksize;
  	n = journal->j_blocksize / sizeof(journal_block_tag_t);
  	journal->j_wbufsize = n;
  	journal->j_wbuf = kmalloc(n * sizeof(struct buffer_head*), GFP_KERNEL);
  	if (!journal->j_wbuf) {
  		printk(KERN_ERR "%s: Cant allocate bhs for commit thread\n",
  			__FUNCTION__);
  		kfree(journal);
  		journal = NULL;
  		goto out;
  	}
  	journal->j_dev = bdev;
  	journal->j_fs_dev = fs_dev;
  	journal->j_blk_offset = start;
  	journal->j_maxlen = len;
  
  	bh = __getblk(journal->j_dev, start, journal->j_blocksize);
  	J_ASSERT(bh != NULL);
  	journal->j_sb_buffer = bh;
  	journal->j_superblock = (journal_superblock_t *)bh->b_data;
  out:
  	return journal;
  }
  
  /**
   *  journal_t * 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();
  	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;
  	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 = jbd2_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 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. */
  	jbd2_journal_update_superblock(journal, 1);
  	jbd2_journal_start_thread(journal);
  	return 0;
  }
  
  /**
   * int jbd2_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 jbd2_journal_create(journal_t *journal)
  {
  	unsigned long long blocknr;
  	struct buffer_head *bh;
  	journal_superblock_t *sb;
  	int i, err;
  
  	if (journal->j_maxlen < JBD2_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 JBD2_MAGIC_NUMBER. */
  	jbd_debug(1, "JBD: Zeroing out journal blocks...\n");
  	for (i = 0; i < journal->j_maxlen; i++) {
  		err = jbd2_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(JBD2_MAGIC_NUMBER);
  	sb->s_header.h_blocktype = cpu_to_be32(JBD2_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 &= ~JBD2_ABORT;
  	journal->j_format_version = 2;
  
  	return journal_reset(journal);
  }
  
  /**
   * void jbd2_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 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;
  	}
  
  	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 &= ~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;
  		}
  	}
  
  	/*
  	 * Create a slab for this blocksize
  	 */
  	err = jbd2_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 (jbd2_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 &= ~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.
   */
  void jbd2_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)
  		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);
  		jbd2_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) {
  		jbd2_journal_update_superblock(journal, 1);
  		brelse(journal->j_sb_buffer);
  	}
  
  	if (journal->j_inode)
  		iput(journal->j_inode);
  	if (journal->j_revoke)
  		jbd2_journal_destroy_revoke(journal);
  	kfree(journal->j_wbuf);
  	kfree(journal);
  }
  
  
  /**
   *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;
  }
  
  
  /**
   * 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);
  		err = jbd2_log_do_checkpoint(journal);
  		spin_lock(&journal->j_list_lock);
  	}
  	spin_unlock(&journal->j_list_lock);
  	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 err;
  }
  
  /**
   * 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_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 __jbd2_journal_abort_hard(journal_t *journal)
  {
  	transaction_t *transaction;
  	char b[BDEVNAME_SIZE];
  
  	if (journal->j_flags & JBD2_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 |= 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 numbet 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 JBD_TAG_SIZE64;
  	else
  		return JBD_TAG_SIZE32;
  }
  
  /*
   * Simple support for retrying memory allocations.  Introduced to help to
   * debug different VM deadlock avoidance strategies.
   */
  void * __jbd2_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 struct kmem_cache *jbd_slab[JBD_MAX_SLABS];
  static const char *jbd_slab_names[JBD_MAX_SLABS] = {
  	"jbd2_1k", "jbd2_2k", "jbd2_4k", NULL, "jbd2_8k"
  };
  
  static void jbd2_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 jbd2_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 * jbd2_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 jbd2_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 struct kmem_cache *jbd2_journal_head_cache;
  #ifdef CONFIG_JBD_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 == 0);
  	jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
  				sizeof(struct journal_head),
  				0,		/* offset */
  				0,		/* flags */
  				NULL,		/* ctor */
  				NULL);		/* dtor */
  	retval = 0;
  	if (jbd2_journal_head_cache == 0) {
  		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)
  {
  	J_ASSERT(jbd2_journal_head_cache != NULL);
  	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_JBD_DEBUG
  	atomic_inc(&nr_journal_heads);
  #endif
  	ret = kmem_cache_alloc(jbd2_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(jbd2_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(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",
  						__FUNCTION__);
  				jbd2_slab_free(jh->b_frozen_data, bh->b_size);
  			}
  			if (jh->b_committed_data) {
  				printk(KERN_WARNING "%s: freeing "
  						"b_committed_data\n",
  						__FUNCTION__);
  				jbd2_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");
  		}
  	}
  }
  
  /*
   * 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);
  }
  
  /*
   * /proc tunables
   */
  #if defined(CONFIG_JBD_DEBUG)
  int jbd2_journal_enable_debug;
  EXPORT_SYMBOL(jbd2_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", jbd2_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';
  	jbd2_journal_enable_debug = simple_strtoul(buf, NULL, 10);
  	return count;
  }
  
  #define JBD_PROC_NAME "sys/fs/jbd2-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 jbd2_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 jbd2_remove_jbd_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 */
  				0,		/* flags */
  				NULL,		/* ctor */
  				NULL);		/* dtor */
  	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();
  	jbd2_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)
  		jbd2_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
  	jbd2_remove_jbd_proc_entry();
  	jbd2_journal_destroy_caches();
  }
  
  MODULE_LICENSE("GPL");
  module_init(journal_init);
  module_exit(journal_exit);
  
  