text: // SPDX-License-Identifier: GPL-2.0+
  /*
   * linux/fs/jbd2/journal.c
   *
   * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
   *
   * Copyright 1998 Red Hat corp --- All Rights Reserved
   *
   * 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/seq_file.h>
  #include <linux/math64.h>
  #include <linux/hash.h>
  #include <linux/log2.h>
  #include <linux/vmalloc.h>
  #include <linux/backing-dev.h>
  #include <linux/bitops.h>
  #include <linux/ratelimit.h>
  #include <linux/sched/mm.h>
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/jbd2.h>
  
  #include <linux/uaccess.h>
  #include <asm/page.h>
  
  #ifdef CONFIG_JBD2_DEBUG
  ushort jbd2_journal_enable_debug __read_mostly;
  EXPORT_SYMBOL(jbd2_journal_enable_debug);
  
  module_param_named(jbd2_debug, jbd2_journal_enable_debug, ushort, 0644);
  MODULE_PARM_DESC(jbd2_debug, "Debugging level for jbd2");
  #endif
  
  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_forget);
  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_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_inode_ranged_write);
  EXPORT_SYMBOL(jbd2_journal_inode_ranged_wait);
  EXPORT_SYMBOL(jbd2_journal_init_jbd_inode);
  EXPORT_SYMBOL(jbd2_journal_release_jbd_inode);
  EXPORT_SYMBOL(jbd2_journal_begin_ordered_truncate);
  EXPORT_SYMBOL(jbd2_inode_cache);
  
  static int jbd2_journal_create_slab(size_t slab_size);
  
  #ifdef CONFIG_JBD2_DEBUG
  void __jbd2_debug(int level, const char *file, const char *func,
  		  unsigned int line, const char *fmt, ...)
  {
  	struct va_format vaf;
  	va_list args;
  
  	if (level > jbd2_journal_enable_debug)
  		return;
  	va_start(args, fmt);
  	vaf.fmt = fmt;
  	vaf.va = &args;
  	printk(KERN_DEBUG "%s: (%s, %u): %pV", file, func, line, &vaf);
  	va_end(args);
  }
  EXPORT_SYMBOL(__jbd2_debug);
  #endif
  
  /* Checksumming functions */
  static int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
  {
  	if (!jbd2_journal_has_csum_v2or3_feature(j))
  		return 1;
  
  	return sb->s_checksum_type == JBD2_CRC32C_CHKSUM;
  }
  
  static __be32 jbd2_superblock_csum(journal_t *j, journal_superblock_t *sb)
  {
  	__u32 csum;
  	__be32 old_csum;
  
  	old_csum = sb->s_checksum;
  	sb->s_checksum = 0;
  	csum = jbd2_chksum(j, ~0, (char *)sb, sizeof(journal_superblock_t));
  	sb->s_checksum = old_csum;
  
  	return cpu_to_be32(csum);
  }
  
  /*
   * Helper function used to manage commit timeouts
   */
  
  static void commit_timeout(struct timer_list *t)
  {
  	journal_t *journal = from_timer(journal, t, j_commit_timer);
  
  	wake_up_process(journal->j_task);
  }
  
  /*
   * 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
  	 */
  	timer_setup(&journal->j_commit_timer, commit_timeout, 0);
  
  	set_freezable();
  
  	/* Record that the journal thread is running */
  	journal->j_task = current;
  	wake_up(&journal->j_wait_done_commit);
  
  	/*
  	 * Make sure that no allocations from this kernel thread will ever
  	 * recurse to the fs layer because we are responsible for the
  	 * transaction commit and any fs involvement might get stuck waiting for
  	 * the trasn. commit.
  	 */
  	memalloc_nofs_save();
  
  	/*
  	 * And now, wait forever for commit wakeup events.
  	 */
  	write_lock(&journal->j_state_lock);
  
  loop:
  	if (journal->j_flags & JBD2_UNMOUNT)
  		goto end_loop;
  
  	jbd_debug(1, "commit_sequence=%u, commit_request=%u\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");
  		write_unlock(&journal->j_state_lock);
  		del_timer_sync(&journal->j_commit_timer);
  		jbd2_journal_commit_transaction(journal);
  		write_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");
  		write_unlock(&journal->j_state_lock);
  		try_to_freeze();
  		write_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) {
  			write_unlock(&journal->j_state_lock);
  			schedule();
  			write_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:
  	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");
  	write_unlock(&journal->j_state_lock);
  	return 0;
  }
  
  static int jbd2_journal_start_thread(journal_t *journal)
  {
  	struct task_struct *t;
  
  	t = kthread_run(kjournald2, journal, "jbd2/%s",
  			journal->j_devname);
  	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)
  {
  	write_lock(&journal->j_state_lock);
  	journal->j_flags |= JBD2_UNMOUNT;
  
  	while (journal->j_task) {
  		write_unlock(&journal->j_state_lock);
  		wake_up(&journal->j_wait_commit);
  		wait_event(journal->j_wait_done_commit, journal->j_task == NULL);
  		write_lock(&journal->j_state_lock);
  	}
  	write_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 make sure nobody modifies it while the
   * IO is in progress. do_get_write_access() handles this.
   *
   * The function returns a pointer to the buffer_head to be used for IO.
   *
   *
   * 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 buffer_head **bh_out,
  				  sector_t blocknr)
  {
  	int need_copy_out = 0;
  	int done_copy_out = 0;
  	int do_escape = 0;
  	char *mapped_data;
  	struct buffer_head *new_bh;
  	struct page *new_page;
  	unsigned int new_offset;
  	struct buffer_head *bh_in = jh2bh(jh_in);
  	journal_t *journal = transaction->t_journal;
  
  	/*
  	 * The buffer really shouldn't be locked: only the current committing
  	 * transaction is allowed to write it, so nobody else is allowed
  	 * to do any IO.
  	 *
  	 * akpm: except if we're journalling data, and write() output is
  	 * also part of a shared mapping, and another thread has
  	 * decided to launch a writepage() against this buffer.
  	 */
  	J_ASSERT_BH(bh_in, buffer_jbddirty(bh_in));
  
  	new_bh = alloc_buffer_head(GFP_NOFS|__GFP_NOFAIL);
  
  	/* keep subsequent assertions sane */
  	atomic_set(&new_bh->b_count, 1);
  
  	jbd_lock_bh_state(bh_in);
  repeat:
  	/*
  	 * If a new transaction has already done a buffer copy-out, then
  	 * we use that version of the data for the commit.
  	 */
  	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);
  	/*
  	 * Fire data frozen trigger if data already wasn't frozen.  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.
  	 */
  	if (!done_copy_out)
  		jbd2_buffer_frozen_trigger(jh_in, mapped_data + new_offset,
  					   jh_in->b_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);
  
  	/*
  	 * 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) {
  			brelse(new_bh);
  			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);
  		memcpy(tmp, mapped_data + new_offset, bh_in->b_size);
  		kunmap_atomic(mapped_data);
  
  		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);
  		*((unsigned int *)(mapped_data + new_offset)) = 0;
  		kunmap_atomic(mapped_data);
  	}
  
  	set_bh_page(new_bh, new_page, new_offset);
  	new_bh->b_size = bh_in->b_size;
  	new_bh->b_bdev = journal->j_dev;
  	new_bh->b_blocknr = blocknr;
  	new_bh->b_private = bh_in;
  	set_buffer_mapped(new_bh);
  	set_buffer_dirty(new_bh);
  
  	*bh_out = new_bh;
  
  	/*
  	 * 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);
  	set_buffer_shadow(bh_in);
  	jbd_unlock_bh_state(bh_in);
  
  	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.
   */
  
  /*
   * Called with j_state_lock locked for writing.
   * Returns true if a transaction commit was started.
   */
  int __jbd2_log_start_commit(journal_t *journal, tid_t target)
  {
  	/* Return if the txn has already requested to be committed */
  	if (journal->j_commit_request == target)
  		return 0;
  
  	/*
  	 * The only transaction we can possibly wait upon is the
  	 * currently running transaction (if it exists).  Otherwise,
  	 * the target tid must be an old one.
  	 */
  	if (journal->j_running_transaction &&
  	    journal->j_running_transaction->t_tid == target) {
  		/*
  		 * We want a new commit: OK, mark the request and wakeup the
  		 * commit thread.  We do _not_ do the commit ourselves.
  		 */
  
  		journal->j_commit_request = target;
  		jbd_debug(1, "JBD2: requesting commit %u/%u\n",
  			  journal->j_commit_request,
  			  journal->j_commit_sequence);
  		journal->j_running_transaction->t_requested = jiffies;
  		wake_up(&journal->j_wait_commit);
  		return 1;
  	} else if (!tid_geq(journal->j_commit_request, target))
  		/* This should never happen, but if it does, preserve
  		   the evidence before kjournald goes into a loop and
  		   increments j_commit_sequence beyond all recognition. */
  		WARN_ONCE(1, "JBD2: bad log_start_commit: %u %u %u %u\n",
  			  journal->j_commit_request,
  			  journal->j_commit_sequence,
  			  target, journal->j_running_transaction ?
  			  journal->j_running_transaction->t_tid : 0);
  	return 0;
  }
  
  int jbd2_log_start_commit(journal_t *journal, tid_t tid)
  {
  	int ret;
  
  	write_lock(&journal->j_state_lock);
  	ret = __jbd2_log_start_commit(journal, tid);
  	write_unlock(&journal->j_state_lock);
  	return ret;
  }
  
  /*
   * Force and wait any uncommitted transactions.  We can only force the running
   * transaction if we don't have an active handle, otherwise, we will deadlock.
   * Returns: <0 in case of error,
   *           0 if nothing to commit,
   *           1 if transaction was successfully committed.
   */
  static int __jbd2_journal_force_commit(journal_t *journal)
  {
  	transaction_t *transaction = NULL;
  	tid_t tid;
  	int need_to_start = 0, ret = 0;
  
  	read_lock(&journal->j_state_lock);
  	if (journal->j_running_transaction && !current->journal_info) {
  		transaction = journal->j_running_transaction;
  		if (!tid_geq(journal->j_commit_request, transaction->t_tid))
  			need_to_start = 1;
  	} else if (journal->j_committing_transaction)
  		transaction = journal->j_committing_transaction;
  
  	if (!transaction) {
  		/* Nothing to commit */
  		read_unlock(&journal->j_state_lock);
  		return 0;
  	}
  	tid = transaction->t_tid;
  	read_unlock(&journal->j_state_lock);
  	if (need_to_start)
  		jbd2_log_start_commit(journal, tid);
  	ret = jbd2_log_wait_commit(journal, tid);
  	if (!ret)
  		ret = 1;
  
  	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.
   *
   * @journal: journal to force
   * Returns true if progress was made.
   */
  int jbd2_journal_force_commit_nested(journal_t *journal)
  {
  	int ret;
  
  	ret = __jbd2_journal_force_commit(journal);
  	return ret > 0;
  }
  
  /**
   * int journal_force_commit() - force any uncommitted transactions
   * @journal: journal to force
   *
   * Caller want unconditional commit. We can only force the running transaction
   * if we don't have an active handle, otherwise, we will deadlock.
   */
  int jbd2_journal_force_commit(journal_t *journal)
  {
  	int ret;
  
  	J_ASSERT(!current->journal_info);
  	ret = __jbd2_journal_force_commit(journal);
  	if (ret > 0)
  		ret = 0;
  	return ret;
  }
  
  /*
   * 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;
  
  	write_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 commit has been started, then we have to wait for
  		 * completion of that transaction.
  		 */
  		if (ptid)
  			*ptid = journal->j_committing_transaction->t_tid;
  		ret = 1;
  	}
  	write_unlock(&journal->j_state_lock);
  	return ret;
  }
  
  /*
   * Return 1 if a given transaction has not yet sent barrier request
   * connected with a transaction commit. If 0 is returned, transaction
   * may or may not have sent the barrier. Used to avoid sending barrier
   * twice in common cases.
   */
  int jbd2_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
  {
  	int ret = 0;
  	transaction_t *commit_trans;
  
  	if (!(journal->j_flags & JBD2_BARRIER))
  		return 0;
  	read_lock(&journal->j_state_lock);
  	/* Transaction already committed? */
  	if (tid_geq(journal->j_commit_sequence, tid))
  		goto out;
  	commit_trans = journal->j_committing_transaction;
  	if (!commit_trans || commit_trans->t_tid != tid) {
  		ret = 1;
  		goto out;
  	}
  	/*
  	 * Transaction is being committed and we already proceeded to
  	 * submitting a flush to fs partition?
  	 */
  	if (journal->j_fs_dev != journal->j_dev) {
  		if (!commit_trans->t_need_data_flush ||
  		    commit_trans->t_state >= T_COMMIT_DFLUSH)
  			goto out;
  	} else {
  		if (commit_trans->t_state >= T_COMMIT_JFLUSH)
  			goto out;
  	}
  	ret = 1;
  out:
  	read_unlock(&journal->j_state_lock);
  	return ret;
  }
  EXPORT_SYMBOL(jbd2_trans_will_send_data_barrier);
  
  /*
   * 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;
  
  	read_lock(&journal->j_state_lock);
  #ifdef CONFIG_PROVE_LOCKING
  	/*
  	 * Some callers make sure transaction is already committing and in that
  	 * case we cannot block on open handles anymore. So don't warn in that
  	 * case.
  	 */
  	if (tid_gt(tid, journal->j_commit_sequence) &&
  	    (!journal->j_committing_transaction ||
  	     journal->j_committing_transaction->t_tid != tid)) {
  		read_unlock(&journal->j_state_lock);
  		jbd2_might_wait_for_commit(journal);
  		read_lock(&journal->j_state_lock);
  	}
  #endif
  #ifdef CONFIG_JBD2_DEBUG
  	if (!tid_geq(journal->j_commit_request, tid)) {
  		printk(KERN_ERR
  		       "%s: error: j_commit_request=%u, tid=%u\n",
  		       __func__, journal->j_commit_request, tid);
  	}
  #endif
  	while (tid_gt(tid, journal->j_commit_sequence)) {
  		jbd_debug(1, "JBD2: want %u, j_commit_sequence=%u\n",
  				  tid, journal->j_commit_sequence);
  		read_unlock(&journal->j_state_lock);
  		wake_up(&journal->j_wait_commit);
  		wait_event(journal->j_wait_done_commit,
  				!tid_gt(tid, journal->j_commit_sequence));
  		read_lock(&journal->j_state_lock);
  	}
  	read_unlock(&journal->j_state_lock);
  
  	if (unlikely(is_journal_aborted(journal)))
  		err = -EIO;
  	return err;
  }
  
  /* Return 1 when transaction with given tid has already committed. */
  int jbd2_transaction_committed(journal_t *journal, tid_t tid)
  {
  	int ret = 1;
  
  	read_lock(&journal->j_state_lock);
  	if (journal->j_running_transaction &&
  	    journal->j_running_transaction->t_tid == tid)
  		ret = 0;
  	if (journal->j_committing_transaction &&
  	    journal->j_committing_transaction->t_tid == tid)
  		ret = 0;
  	read_unlock(&journal->j_state_lock);
  	return ret;
  }
  EXPORT_SYMBOL(jbd2_transaction_committed);
  
  /*
   * When this function returns the transaction corresponding to tid
   * will be completed.  If the transaction has currently running, start
   * committing that transaction before waiting for it to complete.  If
   * the transaction id is stale, it is by definition already completed,
   * so just return SUCCESS.
   */
  int jbd2_complete_transaction(journal_t *journal, tid_t tid)
  {
  	int	need_to_wait = 1;
  
  	read_lock(&journal->j_state_lock);
  	if (journal->j_running_transaction &&
  	    journal->j_running_transaction->t_tid == tid) {
  		if (journal->j_commit_request != tid) {
  			/* transaction not yet started, so request it */
  			read_unlock(&journal->j_state_lock);
  			jbd2_log_start_commit(journal, tid);
  			goto wait_commit;
  		}
  	} else if (!(journal->j_committing_transaction &&
  		     journal->j_committing_transaction->t_tid == tid))
  		need_to_wait = 0;
  	read_unlock(&journal->j_state_lock);
  	if (!need_to_wait)
  		return 0;
  wait_commit:
  	return jbd2_log_wait_commit(journal, tid);
  }
  EXPORT_SYMBOL(jbd2_complete_transaction);
  
  /*
   * Log buffer allocation routines:
   */
  
  int jbd2_journal_next_log_block(journal_t *journal, unsigned long long *retp)
  {
  	unsigned long blocknr;
  
  	write_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;
  	write_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;
  			jbd2_journal_abort(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 buffer_head *
  jbd2_journal_get_descriptor_buffer(transaction_t *transaction, int type)
  {
  	journal_t *journal = transaction->t_journal;
  	struct buffer_head *bh;
  	unsigned long long blocknr;
  	journal_header_t *header;
  	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);
  	header = (journal_header_t *)bh->b_data;
  	header->h_magic = cpu_to_be32(JBD2_MAGIC_NUMBER);
  	header->h_blocktype = cpu_to_be32(type);
  	header->h_sequence = cpu_to_be32(transaction->t_tid);
  	set_buffer_uptodate(bh);
  	unlock_buffer(bh);
  	BUFFER_TRACE(bh, "return this buffer");
  	return bh;
  }
  
  void jbd2_descriptor_block_csum_set(journal_t *j, struct buffer_head *bh)
  {
  	struct jbd2_journal_block_tail *tail;
  	__u32 csum;
  
  	if (!jbd2_journal_has_csum_v2or3(j))
  		return;
  
  	tail = (struct jbd2_journal_block_tail *)(bh->b_data + j->j_blocksize -
  			sizeof(struct jbd2_journal_block_tail));
  	tail->t_checksum = 0;
  	csum = jbd2_chksum(j, j->j_csum_seed, bh->b_data, j->j_blocksize);
  	tail->t_checksum = cpu_to_be32(csum);
  }
  
  /*
   * Return tid of the oldest transaction in the journal and block in the journal
   * where the transaction starts.
   *
   * If the journal is now empty, return which will be the next transaction ID
   * we will write and where will that transaction start.
   *
   * The return value is 0 if journal tail cannot be pushed any further, 1 if
   * it can.
   */
  int jbd2_journal_get_log_tail(journal_t *journal, tid_t *tid,
  			      unsigned long *block)
  {
  	transaction_t *transaction;
  	int ret;
  
  	read_lock(&journal->j_state_lock);
  	spin_lock(&journal->j_list_lock);
  	transaction = journal->j_checkpoint_transactions;
  	if (transaction) {
  		*tid = transaction->t_tid;
  		*block = transaction->t_log_start;
  	} else if ((transaction = journal->j_committing_transaction) != NULL) {
  		*tid = transaction->t_tid;
  		*block = transaction->t_log_start;
  	} else if ((transaction = journal->j_running_transaction) != NULL) {
  		*tid = transaction->t_tid;
  		*block = journal->j_head;
  	} else {
  		*tid = journal->j_transaction_sequence;
  		*block = journal->j_head;
  	}
  	ret = tid_gt(*tid, journal->j_tail_sequence);
  	spin_unlock(&journal->j_list_lock);
  	read_unlock(&journal->j_state_lock);
  
  	return ret;
  }
  
  /*
   * Update information in journal structure and in on disk journal superblock
   * about log tail. This function does not check whether information passed in
   * really pushes log tail further. It's responsibility of the caller to make
   * sure provided log tail information is valid (e.g. by holding
   * j_checkpoint_mutex all the time between computing log tail and calling this
   * function as is the case with jbd2_cleanup_journal_tail()).
   *
   * Requires j_checkpoint_mutex
   */
  int __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block)
  {
  	unsigned long freed;
  	int ret;
  
  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
  
  	/*
  	 * We cannot afford for write to remain in drive's caches since as
  	 * soon as we update j_tail, next transaction can start reusing journal
  	 * space and if we lose sb update during power failure we'd replay
  	 * old transaction with possibly newly overwritten data.
  	 */
  	ret = jbd2_journal_update_sb_log_tail(journal, tid, block,
  					      REQ_SYNC | REQ_FUA);
  	if (ret)
  		goto out;
  
  	write_lock(&journal->j_state_lock);
  	freed = block - journal->j_tail;
  	if (block < journal->j_tail)
  		freed += journal->j_last - journal->j_first;
  
  	trace_jbd2_update_log_tail(journal, tid, block, freed);
  	jbd_debug(1,
  		  "Cleaning journal tail from %u to %u (offset %lu), "
  		  "freeing %lu\n",
  		  journal->j_tail_sequence, tid, block, freed);
  
  	journal->j_free += freed;
  	journal->j_tail_sequence = tid;
  	journal->j_tail = block;
  	write_unlock(&journal->j_state_lock);
  
  out:
  	return ret;
  }
  
  /*
   * This is a variation of __jbd2_update_log_tail which checks for validity of
   * provided log tail and locks j_checkpoint_mutex. So it is safe against races
   * with other threads updating log tail.
   */
  void jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block)
  {
  	mutex_lock_io(&journal->j_checkpoint_mutex);
  	if (tid_gt(tid, journal->j_tail_sequence))
  		__jbd2_update_log_tail(journal, tid, block);
  	mutex_unlock(&journal->j_checkpoint_mutex);
  }
  
  struct jbd2_stats_proc_session {
  	journal_t *journal;
  	struct transaction_stats_s *stats;
  	int start;
  	int max;
  };
  
  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)
  {
  	(*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 transactions (%lu requested), "
  		   "each up to %u blocks\n",
  		   s->stats->ts_tid, s->stats->ts_requested,
  		   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->run.rs_wait / s->stats->ts_tid));
  	seq_printf(seq, "  %ums request delay\n",
  	    (s->stats->ts_requested == 0) ? 0 :
  	    jiffies_to_msecs(s->stats->run.rs_request_delay /
  			     s->stats->ts_requested));
  	seq_printf(seq, "  %ums running transaction\n",
  	    jiffies_to_msecs(s->stats->run.rs_running / s->stats->ts_tid));
  	seq_printf(seq, "  %ums transaction was being locked\n",
  	    jiffies_to_msecs(s->stats->run.rs_locked / s->stats->ts_tid));
  	seq_printf(seq, "  %ums flushing data (in ordered mode)\n",
  	    jiffies_to_msecs(s->stats->run.rs_flushing / s->stats->ts_tid));
  	seq_printf(seq, "  %ums logging transaction\n",
  	    jiffies_to_msecs(s->stats->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->run.rs_handle_count / s->stats->ts_tid);
  	seq_printf(seq, "  %lu blocks per transaction\n",
  	    s->stats->run.rs_blocks / s->stats->ts_tid);
  	seq_printf(seq, "  %lu logged blocks per transaction\n",
  	    s->stats->run.rs_blocks_logged / s->stats->ts_tid);
  	return 0;
  }
  
  static void jbd2_seq_info_stop(struct seq_file *seq, void *v)
  {
  }
  
  static const 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_DATA(inode);
  	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 const 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("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(journal->j_devname, proc_jbd2_stats);
  }
  
  /*
   * 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(struct block_device *bdev,
  			struct block_device *fs_dev,
  			unsigned long long start, int len, int blocksize)
  {
  	static struct lock_class_key jbd2_trans_commit_key;
  	journal_t *journal;
  	int err;
  	struct buffer_head *bh;
  	int n;
  
  	journal = kzalloc(sizeof(*journal), GFP_KERNEL);
  	if (!journal)
  		return NULL;
  
  	init_waitqueue_head(&journal->j_wait_transaction_locked);
  	init_waitqueue_head(&journal->j_wait_done_commit);
  	init_waitqueue_head(&journal->j_wait_commit);
  	init_waitqueue_head(&journal->j_wait_updates);
  	init_waitqueue_head(&journal->j_wait_reserved);
  	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);
  	rwlock_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 */
  	atomic_set(&journal->j_reserved_credits, 0);
  
  	/* 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)
  		goto err_cleanup;
  
  	spin_lock_init(&journal->j_history_lock);
  
  	lockdep_init_map(&journal->j_trans_commit_map, "jbd2_handle",
  			 &jbd2_trans_commit_key, 0);
  
  	/* journal descriptor can store up to n blocks -bzzz */
  	journal->j_blocksize = blocksize;
  	journal->j_dev = bdev;
  	journal->j_fs_dev = fs_dev;
  	journal->j_blk_offset = start;
  	journal->j_maxlen = len;
  	n = journal->j_blocksize / sizeof(journal_block_tag_t);
  	journal->j_wbufsize = n;
  	journal->j_wbuf = kmalloc_array(n, sizeof(struct buffer_head *),
  					GFP_KERNEL);
  	if (!journal->j_wbuf)
  		goto err_cleanup;
  
  	bh = getblk_unmovable(journal->j_dev, start, journal->j_blocksize);
  	if (!bh) {
  		pr_err("%s: Cannot get buffer for journal superblock\n",
  			__func__);
  		goto err_cleanup;
  	}
  	journal->j_sb_buffer = bh;
  	journal->j_superblock = (journal_superblock_t *)bh->b_data;
  
  	return journal;
  
  err_cleanup:
  	kfree(journal->j_wbuf);
  	jbd2_journal_destroy_revoke(journal);
  	kfree(journal);
  	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 = journal_init_common(bdev, fs_dev, start, len, blocksize);
  	if (!journal)
  		return NULL;
  
  	bdevname(journal->j_dev, journal->j_devname);
  	strreplace(journal->j_devname, '/', '!');
  	jbd2_stats_proc_init(journal);
  
  	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)
  {
  	journal_t *journal;
  	char *p;
  	unsigned long long blocknr;
  
  	blocknr = bmap(inode, 0);
  	if (!blocknr) {
  		pr_err("%s: Cannot locate journal superblock\n",
  			__func__);
  		return NULL;
  	}
  
  	jbd_debug(1, "JBD2: inode %s/%ld, size %lld, bits %d, blksize %ld\n",
  		  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 = journal_init_common(inode->i_sb->s_bdev, inode->i_sb->s_bdev,
  			blocknr, inode->i_size >> inode->i_sb->s_blocksize_bits,
  			inode->i_sb->s_blocksize);
  	if (!journal)
  		return NULL;
  
  	journal->j_inode = inode;
  	bdevname(journal->j_dev, journal->j_devname);
  	p = strreplace(journal->j_devname, '/', '!');
  	sprintf(p, "-%lu", journal->j_inode->i_ino);
  	jbd2_stats_proc_init(journal);
  
  	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);
  	if (first + JBD2_MIN_JOURNAL_BLOCKS > last + 1) {
  		printk(KERN_ERR "JBD2: 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;
  
  	/*
  	 * As a special case, if the on-disk copy is already marked as needing
  	 * no recovery (s_start == 0), then we can safely defer the superblock
  	 * update until the next commit by setting JBD2_FLUSHED.  This avoids
  	 * attempting a write to a potential-readonly device.
  	 */
  	if (sb->s_start == 0) {
  		jbd_debug(1, "JBD2: Skipping superblock update on recovered sb "
  			"(start %ld, seq %u, errno %d)\n",
  			journal->j_tail, journal->j_tail_sequence,
  			journal->j_errno);
  		journal->j_flags |= JBD2_FLUSHED;
  	} else {
  		/* Lock here to make assertions happy... */
  		mutex_lock_io(&journal->j_checkpoint_mutex);
  		/*
  		 * Update log tail information. We use REQ_FUA since new
  		 * transaction will start reusing journal space and so we
  		 * must make sure information about current log tail is on
  		 * disk before that.
  		 */
  		jbd2_journal_update_sb_log_tail(journal,
  						journal->j_tail_sequence,
  						journal->j_tail,
  						REQ_SYNC | REQ_FUA);
  		mutex_unlock(&journal->j_checkpoint_mutex);
  	}
  	return jbd2_journal_start_thread(journal);
  }
  
  /*
   * This function expects that the caller will have locked the journal
   * buffer head, and will return with it unlocked
   */
  static int jbd2_write_superblock(journal_t *journal, int write_flags)
  {
  	struct buffer_head *bh = journal->j_sb_buffer;
  	journal_superblock_t *sb = journal->j_superblock;
  	int ret;
  
  	/* Buffer got discarded which means block device got invalidated */
  	if (!buffer_mapped(bh)) {
  		unlock_buffer(bh);
  		return -EIO;
  	}
  
  	trace_jbd2_write_superblock(journal, write_flags);
  	if (!(journal->j_flags & JBD2_BARRIER))
  		write_flags &= ~(REQ_FUA | REQ_PREFLUSH);
  	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);
  	}
  	if (jbd2_journal_has_csum_v2or3(journal))
  		sb->s_checksum = jbd2_superblock_csum(journal, sb);
  	get_bh(bh);
  	bh->b_end_io = end_buffer_write_sync;
  	ret = submit_bh(REQ_OP_WRITE, write_flags, bh);
  	wait_on_buffer(bh);
  	if (buffer_write_io_error(bh)) {
  		clear_buffer_write_io_error(bh);
  		set_buffer_uptodate(bh);
  		ret = -EIO;
  	}
  	if (ret) {
  		printk(KERN_ERR "JBD2: Error %d detected when updating "
  		       "journal superblock for %s.\n", ret,
  		       journal->j_devname);
  		jbd2_journal_abort(journal, ret);
  	}
  
  	return ret;
  }
  
  /**
   * jbd2_journal_update_sb_log_tail() - Update log tail in journal sb on disk.
   * @journal: The journal to update.
   * @tail_tid: TID of the new transaction at the tail of the log
   * @tail_block: The first block of the transaction at the tail of the log
   * @write_op: With which operation should we write the journal sb
   *
   * Update a journal's superblock information about log tail and write it to
   * disk, waiting for the IO to complete.
   */
  int jbd2_journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
  				     unsigned long tail_block, int write_op)
  {
  	journal_superblock_t *sb = journal->j_superblock;
  	int ret;
  
  	if (is_journal_aborted(journal))
  		return -EIO;
  
  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
  	jbd_debug(1, "JBD2: updating superblock (start %lu, seq %u)\n",
  		  tail_block, tail_tid);
  
  	lock_buffer(journal->j_sb_buffer);
  	sb->s_sequence = cpu_to_be32(tail_tid);
  	sb->s_start    = cpu_to_be32(tail_block);
  
  	ret = jbd2_write_superblock(journal, write_op);
  	if (ret)
  		goto out;
  
  	/* Log is no longer empty */
  	write_lock(&journal->j_state_lock);
  	WARN_ON(!sb->s_sequence);
  	journal->j_flags &= ~JBD2_FLUSHED;
  	write_unlock(&journal->j_state_lock);
  
  out:
  	return ret;
  }
  
  /**
   * jbd2_mark_journal_empty() - Mark on disk journal as empty.
   * @journal: The journal to update.
   * @write_op: With which operation should we write the journal sb
   *
   * Update a journal's dynamic superblock fields to show that journal is empty.
   * Write updated superblock to disk waiting for IO to complete.
   */
  static void jbd2_mark_journal_empty(journal_t *journal, int write_op)
  {
  	journal_superblock_t *sb = journal->j_superblock;
  
  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
  	lock_buffer(journal->j_sb_buffer);
  	if (sb->s_start == 0) {		/* Is it already empty? */
  		unlock_buffer(journal->j_sb_buffer);
  		return;
  	}
  
  	jbd_debug(1, "JBD2: Marking journal as empty (seq %u)\n",
  		  journal->j_tail_sequence);
  
  	sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
  	sb->s_start    = cpu_to_be32(0);
  
  	jbd2_write_superblock(journal, write_op);
  
  	/* Log is no longer empty */
  	write_lock(&journal->j_state_lock);
  	journal->j_flags |= JBD2_FLUSHED;
  	write_unlock(&journal->j_state_lock);
  }
  
  
  /**
   * jbd2_journal_update_sb_errno() - Update error in the journal.
   * @journal: The journal to update.
   *
   * Update a journal's errno.  Write updated superblock to disk waiting for IO
   * to complete.
   */
  void jbd2_journal_update_sb_errno(journal_t *journal)
  {
  	journal_superblock_t *sb = journal->j_superblock;
  	int errcode;
  
  	lock_buffer(journal->j_sb_buffer);
  	errcode = journal->j_errno;
  	if (errcode == -ESHUTDOWN)
  		errcode = 0;
  	jbd_debug(1, "JBD2: updating superblock error (errno %d)\n", errcode);
  	sb->s_errno    = cpu_to_be32(errcode);
  
  	jbd2_write_superblock(journal, REQ_SYNC | REQ_FUA);
  }
  EXPORT_SYMBOL(jbd2_journal_update_sb_errno);
  
  /*
   * 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(REQ_OP_READ, 0, 1, &bh);
  		wait_on_buffer(bh);
  		if (!buffer_uptodate(bh)) {
  			printk(KERN_ERR
  				"JBD2: IO error reading journal superblock\n");
  			goto out;
  		}
  	}
  
  	if (buffer_verified(bh))
  		return 0;
  
  	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 "JBD2: 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 "JBD2: 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 "JBD2: journal file too short\n");
  		goto out;
  	}
  
  	if (be32_to_cpu(sb->s_first) == 0 ||
  	    be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
  		printk(KERN_WARNING
  			"JBD2: Invalid start block of journal: %u\n",
  			be32_to_cpu(sb->s_first));
  		goto out;
  	}
  
  	if (jbd2_has_feature_csum2(journal) &&
  	    jbd2_has_feature_csum3(journal)) {
  		/* Can't have checksum v2 and v3 at the same time! */
  		printk(KERN_ERR "JBD2: Can't enable checksumming v2 and v3 "
  		       "at the same time!\n");
  		goto out;
  	}
  
  	if (jbd2_journal_has_csum_v2or3_feature(journal) &&
  	    jbd2_has_feature_checksum(journal)) {
  		/* Can't have checksum v1 and v2 on at the same time! */
  		printk(KERN_ERR "JBD2: Can't enable checksumming v1 and v2/3 "
  		       "at the same time!\n");
  		goto out;
  	}
  
  	if (!jbd2_verify_csum_type(journal, sb)) {
  		printk(KERN_ERR "JBD2: Unknown checksum type\n");
  		goto out;
  	}
  
  	/* Load the checksum driver */
  	if (jbd2_journal_has_csum_v2or3_feature(journal)) {
  		journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
  		if (IS_ERR(journal->j_chksum_driver)) {
  			printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
  			err = PTR_ERR(journal->j_chksum_driver);
  			journal->j_chksum_driver = NULL;
  			goto out;
  		}
  	}
  
  	if (jbd2_journal_has_csum_v2or3(journal)) {
  		/* Check superblock checksum */
  		if (sb->s_checksum != jbd2_superblock_csum(journal, sb)) {
  			printk(KERN_ERR "JBD2: journal checksum error\n");
  			err = -EFSBADCRC;
  			goto out;
  		}
  
  		/* Precompute checksum seed for all metadata */
  		journal->j_csum_seed = jbd2_chksum(journal, ~0, sb->s_uuid,
  						   sizeof(sb->s_uuid));
  	}
  
  	set_buffer_verified(bh);
  
  	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
  				"JBD2: Unrecognised features on journal\n");
  			return -EINVAL;
  		}
  	}
  
  	/*
  	 * Create a slab for this blocksize
  	 */
  	err = jbd2_journal_create_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;
  
  	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 -EFSCORRUPTED;
  	}
  	/*
  	 * clear JBD2_ABORT flag initialized in journal_init_common
  	 * here to update log tail information with the newest seq.
  	 */
  	journal->j_flags &= ~JBD2_ABORT;
  
  	/* 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_LOADED;
  	return 0;
  
  recovery_error:
  	printk(KERN_WARNING "JBD2: 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_io(&journal->j_checkpoint_mutex);
  		err = jbd2_log_do_checkpoint(journal);
  		mutex_unlock(&journal->j_checkpoint_mutex);
  		/*
  		 * If checkpointing failed, just free the buffers to avoid
  		 * looping forever
  		 */
  		if (err) {
  			jbd2_journal_destroy_checkpoint(journal);
  			spin_lock(&journal->j_list_lock);
  			break;
  		}
  		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)) {
  			mutex_lock_io(&journal->j_checkpoint_mutex);
  
  			write_lock(&journal->j_state_lock);
  			journal->j_tail_sequence =
  				++journal->j_transaction_sequence;
  			write_unlock(&journal->j_state_lock);
  
  			jbd2_mark_journal_empty(journal,
  					REQ_SYNC | REQ_PREFLUSH | REQ_FUA);
  			mutex_unlock(&journal->j_checkpoint_mutex);
  		} else
  			err = -EIO;
  		brelse(journal->j_sb_buffer);
  	}
  
  	if (journal->j_proc_entry)
  		jbd2_stats_proc_exit(journal);
  	iput(journal->j_inode);
  	if (journal->j_revoke)
  		jbd2_journal_destroy_revoke(journal);
  	if (journal->j_chksum_driver)
  		crypto_free_shash(journal->j_chksum_driver);
  	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;
  	/* Load journal superblock if it is not loaded yet. */
  	if (journal->j_format_version == 0 &&
  	    journal_get_superblock(journal) != 0)
  		return 0;
  	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)
  {
  	if (!compat && !ro && !incompat)
  		return 1;
  
  	/* We can support any known requested features iff the
  	 * superblock is in version 2.  Otherwise we fail to support any
  	 * extended sb features. */
  
  	if (journal->j_format_version != 2)
  		return 0;
  
  	if ((compat   & 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)
  {
  #define INCOMPAT_FEATURE_ON(f) \
  		((incompat & (f)) && !(sb->s_feature_incompat & cpu_to_be32(f)))
  #define COMPAT_FEATURE_ON(f) \
  		((compat & (f)) && !(sb->s_feature_compat & cpu_to_be32(f)))
  	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;
  
  	/* If enabling v2 checksums, turn on v3 instead */
  	if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V2) {
  		incompat &= ~JBD2_FEATURE_INCOMPAT_CSUM_V2;
  		incompat |= JBD2_FEATURE_INCOMPAT_CSUM_V3;
  	}
  
  	/* Asking for checksumming v3 and v1?  Only give them v3. */
  	if (incompat & JBD2_FEATURE_INCOMPAT_CSUM_V3 &&
  	    compat & JBD2_FEATURE_COMPAT_CHECKSUM)
  		compat &= ~JBD2_FEATURE_COMPAT_CHECKSUM;
  
  	jbd_debug(1, "Setting new features 0x%lx/0x%lx/0x%lx\n",
  		  compat, ro, incompat);
  
  	sb = journal->j_superblock;
  
  	/* Load the checksum driver if necessary */
  	if ((journal->j_chksum_driver == NULL) &&
  	    INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
  		journal->j_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
  		if (IS_ERR(journal->j_chksum_driver)) {
  			printk(KERN_ERR "JBD2: Cannot load crc32c driver.\n");
  			journal->j_chksum_driver = NULL;
  			return 0;
  		}
  		/* Precompute checksum seed for all metadata */
  		journal->j_csum_seed = jbd2_chksum(journal, ~0, sb->s_uuid,
  						   sizeof(sb->s_uuid));
  	}
  
  	lock_buffer(journal->j_sb_buffer);
  
  	/* If enabling v3 checksums, update superblock */
  	if (INCOMPAT_FEATURE_ON(JBD2_FEATURE_INCOMPAT_CSUM_V3)) {
  		sb->s_checksum_type = JBD2_CRC32C_CHKSUM;
  		sb->s_feature_compat &=
  			~cpu_to_be32(JBD2_FEATURE_COMPAT_CHECKSUM);
  	}
  
  	/* If enabling v1 checksums, downgrade superblock */
  	if (COMPAT_FEATURE_ON(JBD2_FEATURE_COMPAT_CHECKSUM))
  		sb->s_feature_incompat &=
  			~cpu_to_be32(JBD2_FEATURE_INCOMPAT_CSUM_V2 |
  				     JBD2_FEATURE_INCOMPAT_CSUM_V3);
  
  	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);
  	unlock_buffer(journal->j_sb_buffer);
  
  	return 1;
  #undef COMPAT_FEATURE_ON
  #undef INCOMPAT_FEATURE_ON
  }
  
  /*
   * 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_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;
  
  	write_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;
  
  		write_unlock(&journal->j_state_lock);
  		jbd2_log_wait_commit(journal, tid);
  	} else {
  		write_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_io(&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;
  
  	mutex_lock_io(&journal->j_checkpoint_mutex);
  	if (!err) {
  		err = jbd2_cleanup_journal_tail(journal);
  		if (err < 0) {
  			mutex_unlock(&journal->j_checkpoint_mutex);
  			goto out;
  		}
  		err = 0;
  	}
  
  	/* 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. */
  	jbd2_mark_journal_empty(journal, REQ_SYNC | REQ_FUA);
  	mutex_unlock(&journal->j_checkpoint_mutex);
  	write_lock(&journal->j_state_lock);
  	J_ASSERT(!journal->j_running_transaction);
  	J_ASSERT(!journal->j_committing_transaction);
  	J_ASSERT(!journal->j_checkpoint_transactions);
  	J_ASSERT(journal->j_head == journal->j_tail);
  	J_ASSERT(journal->j_tail_sequence == journal->j_transaction_sequence);
  	write_unlock(&journal->j_state_lock);
  out:
  	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)
  {
  	int err = 0;
  
  	J_ASSERT (!(journal->j_flags & JBD2_LOADED));
  
  	err = load_superblock(journal);
  	if (err)
  		return err;
  
  	if (!journal->j_tail)
  		goto no_recovery;
  
  	printk(KERN_WARNING "JBD2: %s recovery information on journal\n",
  		write ? "Clearing" : "Ignoring");
  
  	err = jbd2_journal_skip_recovery(journal);
  	if (write) {
  		/* Lock to make assertions happy... */
  		mutex_lock_io(&journal->j_checkpoint_mutex);
  		jbd2_mark_journal_empty(journal, REQ_SYNC | REQ_FUA);
  		mutex_unlock(&journal->j_checkpoint_mutex);
  	}
  
   no_recovery:
  	return err;
  }
  
  /**
   * 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.
   *
   */
  
  void jbd2_journal_abort(journal_t *journal, int errno)
  {
  	transaction_t *transaction;
  
  	/*
  	 * ESHUTDOWN always takes precedence because a file system check
  	 * caused by any other journal abort error is not required after
  	 * a shutdown triggered.
  	 */
  	write_lock(&journal->j_state_lock);
  	if (journal->j_flags & JBD2_ABORT) {
  		int old_errno = journal->j_errno;
  
  		write_unlock(&journal->j_state_lock);
  		if (old_errno != -ESHUTDOWN && errno == -ESHUTDOWN) {
  			journal->j_errno = errno;
  			jbd2_journal_update_sb_errno(journal);
  		}
  		return;
  	}
  
  	/*
  	 * Mark the abort as occurred and start current running transaction
  	 * to release all journaled buffer.
  	 */
  	pr_err("Aborting journal on device %s.\n", journal->j_devname);
  
  	journal->j_flags |= JBD2_ABORT;
  	journal->j_errno = errno;
  	transaction = journal->j_running_transaction;
  	if (transaction)
  		__jbd2_log_start_commit(journal, transaction->t_tid);
  	write_unlock(&journal->j_state_lock);
  
  	/*
  	 * Record errno to the journal super block, so that fsck and jbd2
  	 * layer could realise that a filesystem check is needed.
  	 */
  	jbd2_journal_update_sb_errno(journal);
  
  	write_lock(&journal->j_state_lock);
  	journal->j_flags |= JBD2_REC_ERR;
  	write_unlock(&journal->j_state_lock);
  }
  
  /**
   * 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;
  
  	read_lock(&journal->j_state_lock);
  	if (journal->j_flags & JBD2_ABORT)
  		err = -EROFS;
  	else
  		err = journal->j_errno;
  	read_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;
  
  	write_lock(&journal->j_state_lock);
  	if (journal->j_flags & JBD2_ABORT)
  		err = -EROFS;
  	else
  		journal->j_errno = 0;
  	write_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)
  {
  	write_lock(&journal->j_state_lock);
  	if (journal->j_errno)
  		journal->j_flags |= JBD2_ACK_ERR;
  	write_unlock(&journal->j_state_lock);
  }
  
  int jbd2_journal_blocks_per_page(struct inode *inode)
  {
  	return 1 << (PAGE_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)
  {
  	size_t sz;
  
  	if (jbd2_has_feature_csum3(journal))
  		return sizeof(journal_block_tag3_t);
  
  	sz = sizeof(journal_block_tag_t);
  
  	if (jbd2_has_feature_csum2(journal))
  		sz += sizeof(__u16);
  
  	if (jbd2_has_feature_64bit(journal))
  		return sz;
  	else
  		return sz - sizeof(__u32);
  }
  
  /*
   * JBD memory management
   *
   * These functions are used to allocate block-sized chunks of memory
   * used for making copies of buffer_head data.  Very often it will be
   * page-sized chunks of data, but sometimes it will be in
   * sub-page-size chunks.  (For example, 16k pages on Power systems
   * with a 4k block file system.)  For blocks smaller than a page, we
   * use a SLAB allocator.  There are slab caches for each block size,
   * which are allocated at mount time, if necessary, and we only free
   * (all of) the slab caches when/if the jbd2 module is unloaded.  For
   * this reason we don't need to a mutex to protect access to
   * jbd2_slab[] allocating or releasing memory; only in
   * jbd2_journal_create_slab().
   */
  #define JBD2_MAX_SLABS 8
  static struct kmem_cache *jbd2_slab[JBD2_MAX_SLABS];
  
  static const char *jbd2_slab_names[JBD2_MAX_SLABS] = {
  	"jbd2_1k", "jbd2_2k", "jbd2_4k", "jbd2_8k",
  	"jbd2_16k", "jbd2_32k", "jbd2_64k", "jbd2_128k"
  };
  
  
  static void jbd2_journal_destroy_slabs(void)
  {
  	int i;
  
  	for (i = 0; i < JBD2_MAX_SLABS; i++) {
  		kmem_cache_destroy(jbd2_slab[i]);
  		jbd2_slab[i] = NULL;
  	}
  }
  
  static int jbd2_journal_create_slab(size_t size)
  {
  	static DEFINE_MUTEX(jbd2_slab_create_mutex);
  	int i = order_base_2(size) - 10;
  	size_t slab_size;
  
  	if (size == PAGE_SIZE)
  		return 0;
  
  	if (i >= JBD2_MAX_SLABS)
  		return -EINVAL;
  
  	if (unlikely(i < 0))
  		i = 0;
  	mutex_lock(&jbd2_slab_create_mutex);
  	if (jbd2_slab[i]) {
  		mutex_unlock(&jbd2_slab_create_mutex);
  		return 0;	/* Already created */
  	}
  
  	slab_size = 1 << (i+10);
  	jbd2_slab[i] = kmem_cache_create(jbd2_slab_names[i], slab_size,
  					 slab_size, 0, NULL);
  	mutex_unlock(&jbd2_slab_create_mutex);
  	if (!jbd2_slab[i]) {
  		printk(KERN_EMERG "JBD2: no memory for jbd2_slab cache\n");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static struct kmem_cache *get_slab(size_t size)
  {
  	int i = order_base_2(size) - 10;
  
  	BUG_ON(i >= JBD2_MAX_SLABS);
  	if (unlikely(i < 0))
  		i = 0;
  	BUG_ON(jbd2_slab[i] == NULL);
  	return jbd2_slab[i];
  }
  
  void *jbd2_alloc(size_t size, gfp_t flags)
  {
  	void *ptr;
  
  	BUG_ON(size & (size-1)); /* Must be a power of 2 */
  
  	if (size < PAGE_SIZE)
  		ptr = kmem_cache_alloc(get_slab(size), flags);
  	else
  		ptr = (void *)__get_free_pages(flags, get_order(size));
  
  	/* Check alignment; SLUB has gotten this wrong in the past,
  	 * and this can lead to user data corruption! */
  	BUG_ON(((unsigned long) ptr) & (size-1));
  
  	return ptr;
  }
  
  void jbd2_free(void *ptr, size_t size)
  {
  	if (size < PAGE_SIZE)
  		kmem_cache_free(get_slab(size), ptr);
  	else
  		free_pages((unsigned long)ptr, get_order(size));
  };
  
  /*
   * 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 __init jbd2_journal_init_journal_head_cache(void)
  {
  	J_ASSERT(!jbd2_journal_head_cache);
  	jbd2_journal_head_cache = kmem_cache_create("jbd2_journal_head",
  				sizeof(struct journal_head),
  				0,		/* offset */
  				SLAB_TEMPORARY | SLAB_TYPESAFE_BY_RCU,
  				NULL);		/* ctor */
  	if (!jbd2_journal_head_cache) {
  		printk(KERN_EMERG "JBD2: no memory for journal_head cache\n");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static void jbd2_journal_destroy_journal_head_cache(void)
  {
  	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;
  
  #ifdef CONFIG_JBD2_DEBUG
  	atomic_inc(&nr_journal_heads);
  #endif
  	ret = kmem_cache_zalloc(jbd2_journal_head_cache, GFP_NOFS);
  	if (!ret) {
  		jbd_debug(1, "out of memory for journal_head\n");
  		pr_notice_ratelimited("ENOMEM in %s, retrying.\n", __func__);
  		ret = kmem_cache_zalloc(jbd2_journal_head_cache,
  				GFP_NOFS | __GFP_NOFAIL);
  	}
  	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 is detached from its buffer_head when the journal_head's
   * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
   * transaction (b_cp_transaction) hold their references to b_jcount.
   *
   * Various places in the kernel want to attach a journal_head to a buffer_head
   * _before_ attaching the journal_head to a transaction.  To protect the
   * journal_head in this situation, 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);
   *	...
   *      (Get another reference for transaction)
   *	jbd2_journal_grab_journal_head(bh);
   *	jh->b_transaction = xxx;
   *	(Put original reference)
   *	jbd2_journal_put_journal_head(jh);
   */
  
  /*
   * Give a buffer_head a journal_head.
   *
   * 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();
  
  	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);
  	J_ASSERT_JH(jh, jh->b_transaction == NULL);
  	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
  	J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
  	J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
  	J_ASSERT_BH(bh, buffer_jbd(bh));
  	J_ASSERT_BH(bh, jh2bh(jh) == bh);
  	BUFFER_TRACE(bh, "remove journal_head");
  	if (jh->b_frozen_data) {
  		printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
  		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);
  	journal_free_journal_head(jh);
  }
  
  /*
   * Drop a reference on the passed journal_head.  If it fell to zero then
   * release the journal_head from the buffer_head.
   */
  void 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) {
  		__journal_remove_journal_head(bh);
  		jbd_unlock_bh_journal_head(bh);
  		__brelse(bh);
  	} else
  		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;
  	jinode->i_dirty_start = 0;
  	jinode->i_dirty_end = 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)
  {
  	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.wq_entry, TASK_UNINTERRUPTIBLE);
  		spin_unlock(&journal->j_list_lock);
  		schedule();
  		finish_wait(wq, &wait.wq_entry);
  		goto restart;
  	}
  
  	if (jinode->i_transaction) {
  		list_del(&jinode->i_list);
  		jinode->i_transaction = NULL;
  	}
  	spin_unlock(&journal->j_list_lock);
  }
  
  
  #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, *jbd2_inode_cache;
  
  static int __init jbd2_journal_init_inode_cache(void)
  {
  	J_ASSERT(!jbd2_inode_cache);
  	jbd2_inode_cache = KMEM_CACHE(jbd2_inode, 0);
  	if (!jbd2_inode_cache) {
  		pr_emerg("JBD2: failed to create inode cache\n");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static int __init jbd2_journal_init_handle_cache(void)
  {
  	J_ASSERT(!jbd2_handle_cache);
  	jbd2_handle_cache = KMEM_CACHE(jbd2_journal_handle, SLAB_TEMPORARY);
  	if (!jbd2_handle_cache) {
  		printk(KERN_EMERG "JBD2: failed to create handle cache\n");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static void jbd2_journal_destroy_inode_cache(void)
  {
  	kmem_cache_destroy(jbd2_inode_cache);
  	jbd2_inode_cache = NULL;
  }
  
  static void jbd2_journal_destroy_handle_cache(void)
  {
  	kmem_cache_destroy(jbd2_handle_cache);
  	jbd2_handle_cache = NULL;
  }
  
  /*
   * Module startup and shutdown
   */
  
  static int __init journal_init_caches(void)
  {
  	int ret;
  
  	ret = jbd2_journal_init_revoke_record_cache();
  	if (ret == 0)
  		ret = jbd2_journal_init_revoke_table_cache();
  	if (ret == 0)
  		ret = jbd2_journal_init_journal_head_cache();
  	if (ret == 0)
  		ret = jbd2_journal_init_handle_cache();
  	if (ret == 0)
  		ret = jbd2_journal_init_inode_cache();
  	if (ret == 0)
  		ret = jbd2_journal_init_transaction_cache();
  	return ret;
  }
  
  static void jbd2_journal_destroy_caches(void)
  {
  	jbd2_journal_destroy_revoke_record_cache();
  	jbd2_journal_destroy_revoke_table_cache();
  	jbd2_journal_destroy_journal_head_cache();
  	jbd2_journal_destroy_handle_cache();
  	jbd2_journal_destroy_inode_cache();
  	jbd2_journal_destroy_transaction_cache();
  	jbd2_journal_destroy_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_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_ERR "JBD2: leaked %d journal_heads!\n", n);
  #endif
  	jbd2_remove_jbd_stats_proc_entry();
  	jbd2_journal_destroy_caches();
  }
  
  MODULE_LICENSE("GPL");
  module_init(journal_init);
  module_exit(journal_exit);
  
  