Initial import

1 files changed, 2145 insertions, 0 deletions

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
new file mode 100644
index 000000000..c46a79adb
--- /dev/null
+++ b/fs/jbd/journal.c
@@ -0,0 +1,2145 @@
+/*
+ * linux/fs/jbd/journal.c
+ *
+ * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
+ *
+ * Copyright 1998 Red Hat corp --- All Rights Reserved
+ *
+ * This file is part of the Linux kernel and is made available under
+ * the terms of the GNU General Public License, version 2, or at your
+ * option, any later version, incorporated herein by reference.
+ *
+ * Generic filesystem journal-writing code; part of the ext2fs
+ * journaling system.
+ *
+ * This file manages journals: areas of disk reserved for logging
+ * transactional updates.  This includes the kernel journaling thread
+ * which is responsible for scheduling updates to the log.
+ *
+ * We do not actually manage the physical storage of the journal in this
+ * file: that is left to a per-journal policy function, which allows us
+ * to store the journal within a filesystem-specified area for ext2
+ * journaling (ext2 can use a reserved inode for storing the log).
+ */
+
+#include <linux/module.h>
+#include <linux/time.h>
+#include <linux/fs.h>
+#include <linux/jbd.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/freezer.h>
+#include <linux/pagemap.h>
+#include <linux/kthread.h>
+#include <linux/poison.h>
+#include <linux/proc_fs.h>
+#include <linux/debugfs.h>
+#include <linux/ratelimit.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/jbd.h>
+
+#include <asm/uaccess.h>
+#include <asm/page.h>
+
+EXPORT_SYMBOL(journal_start);
+EXPORT_SYMBOL(journal_restart);
+EXPORT_SYMBOL(journal_extend);
+EXPORT_SYMBOL(journal_stop);
+EXPORT_SYMBOL(journal_lock_updates);
+EXPORT_SYMBOL(journal_unlock_updates);
+EXPORT_SYMBOL(journal_get_write_access);
+EXPORT_SYMBOL(journal_get_create_access);
+EXPORT_SYMBOL(journal_get_undo_access);
+EXPORT_SYMBOL(journal_dirty_data);
+EXPORT_SYMBOL(journal_dirty_metadata);
+EXPORT_SYMBOL(journal_release_buffer);
+EXPORT_SYMBOL(journal_forget);
+#if 0
+EXPORT_SYMBOL(journal_sync_buffer);
+#endif
+EXPORT_SYMBOL(journal_flush);
+EXPORT_SYMBOL(journal_revoke);
+
+EXPORT_SYMBOL(journal_init_dev);
+EXPORT_SYMBOL(journal_init_inode);
+EXPORT_SYMBOL(journal_update_format);
+EXPORT_SYMBOL(journal_check_used_features);
+EXPORT_SYMBOL(journal_check_available_features);
+EXPORT_SYMBOL(journal_set_features);
+EXPORT_SYMBOL(journal_create);
+EXPORT_SYMBOL(journal_load);
+EXPORT_SYMBOL(journal_destroy);
+EXPORT_SYMBOL(journal_abort);
+EXPORT_SYMBOL(journal_errno);
+EXPORT_SYMBOL(journal_ack_err);
+EXPORT_SYMBOL(journal_clear_err);
+EXPORT_SYMBOL(log_wait_commit);
+EXPORT_SYMBOL(log_start_commit);
+EXPORT_SYMBOL(journal_start_commit);
+EXPORT_SYMBOL(journal_force_commit_nested);
+EXPORT_SYMBOL(journal_wipe);
+EXPORT_SYMBOL(journal_blocks_per_page);
+EXPORT_SYMBOL(journal_invalidatepage);
+EXPORT_SYMBOL(journal_try_to_free_buffers);
+EXPORT_SYMBOL(journal_force_commit);
+
+static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
+static void __journal_abort_soft (journal_t *journal, int errno);
+static const char *journal_dev_name(journal_t *journal, char *buffer);
+
+#ifdef CONFIG_JBD_DEBUG
+void __jbd_debug(int level, const char *file, const char *func,
+		 unsigned int line, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	if (level > journal_enable_debug)
+		return;
+	va_start(args, fmt);
+	vaf.fmt = fmt;
+	vaf.va = &args;
+	printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
+	va_end(args);
+}
+EXPORT_SYMBOL(__jbd_debug);
+#endif
+
+/*
+ * Helper function used to manage commit timeouts
+ */
+
+static void commit_timeout(unsigned long __data)
+{
+	struct task_struct * p = (struct task_struct *) __data;
+
+	wake_up_process(p);
+}
+
+/*
+ * kjournald: The main thread function used to manage a logging device
+ * journal.
+ *
+ * This kernel thread is responsible for two things:
+ *
+ * 1) COMMIT:  Every so often we need to commit the current state of the
+ *    filesystem to disk.  The journal thread is responsible for writing
+ *    all of the metadata buffers to disk.
+ *
+ * 2) CHECKPOINT: We cannot reuse a used section of the log file until all
+ *    of the data in that part of the log has been rewritten elsewhere on
+ *    the disk.  Flushing these old buffers to reclaim space in the log is
+ *    known as checkpointing, and this thread is responsible for that job.
+ */
+
+static int kjournald(void *arg)
+{
+	journal_t *journal = arg;
+	transaction_t *transaction;
+
+	/*
+	 * Set up an interval timer which can be used to trigger a commit wakeup
+	 * after the commit interval expires
+	 */
+	setup_timer(&journal->j_commit_timer, commit_timeout,
+			(unsigned long)current);
+
+	set_freezable();
+
+	/* Record that the journal thread is running */
+	journal->j_task = current;
+	wake_up(&journal->j_wait_done_commit);
+
+	printk(KERN_INFO "kjournald starting.  Commit interval %ld seconds\n",
+			journal->j_commit_interval / HZ);
+
+	/*
+	 * And now, wait forever for commit wakeup events.
+	 */
+	spin_lock(&journal->j_state_lock);
+
+loop:
+	if (journal->j_flags & JFS_UNMOUNT)
+		goto end_loop;
+
+	jbd_debug(1, "commit_sequence=%d, commit_request=%d\n",
+		journal->j_commit_sequence, journal->j_commit_request);
+
+	if (journal->j_commit_sequence != journal->j_commit_request) {
+		jbd_debug(1, "OK, requests differ\n");
+		spin_unlock(&journal->j_state_lock);
+		del_timer_sync(&journal->j_commit_timer);
+		journal_commit_transaction(journal);
+		spin_lock(&journal->j_state_lock);
+		goto loop;
+	}
+
+	wake_up(&journal->j_wait_done_commit);
+	if (freezing(current)) {
+		/*
+		 * The simpler the better. Flushing journal isn't a
+		 * good idea, because that depends on threads that may
+		 * be already stopped.
+		 */
+		jbd_debug(1, "Now suspending kjournald\n");
+		spin_unlock(&journal->j_state_lock);
+		try_to_freeze();
+		spin_lock(&journal->j_state_lock);
+	} else {
+		/*
+		 * We assume on resume that commits are already there,
+		 * so we don't sleep
+		 */
+		DEFINE_WAIT(wait);
+		int should_sleep = 1;
+
+		prepare_to_wait(&journal->j_wait_commit, &wait,
+				TASK_INTERRUPTIBLE);
+		if (journal->j_commit_sequence != journal->j_commit_request)
+			should_sleep = 0;
+		transaction = journal->j_running_transaction;
+		if (transaction && time_after_eq(jiffies,
+						transaction->t_expires))
+			should_sleep = 0;
+		if (journal->j_flags & JFS_UNMOUNT)
+			should_sleep = 0;
+		if (should_sleep) {
+			spin_unlock(&journal->j_state_lock);
+			schedule();
+			spin_lock(&journal->j_state_lock);
+		}
+		finish_wait(&journal->j_wait_commit, &wait);
+	}
+
+	jbd_debug(1, "kjournald wakes\n");
+
+	/*
+	 * Were we woken up by a commit wakeup event?
+	 */
+	transaction = journal->j_running_transaction;
+	if (transaction && time_after_eq(jiffies, transaction->t_expires)) {
+		journal->j_commit_request = transaction->t_tid;
+		jbd_debug(1, "woke because of timeout\n");
+	}
+	goto loop;
+
+end_loop:
+	spin_unlock(&journal->j_state_lock);
+	del_timer_sync(&journal->j_commit_timer);
+	journal->j_task = NULL;
+	wake_up(&journal->j_wait_done_commit);
+	jbd_debug(1, "Journal thread exiting.\n");
+	return 0;
+}
+
+static int journal_start_thread(journal_t *journal)
+{
+	struct task_struct *t;
+
+	t = kthread_run(kjournald, journal, "kjournald");
+	if (IS_ERR(t))
+		return PTR_ERR(t);
+
+	wait_event(journal->j_wait_done_commit, journal->j_task != NULL);
+	return 0;
+}
+
+static void journal_kill_thread(journal_t *journal)
+{
+	spin_lock(&journal->j_state_lock);
+	journal->j_flags |= JFS_UNMOUNT;
+
+	while (journal->j_task) {
+		wake_up(&journal->j_wait_commit);
+		spin_unlock(&journal->j_state_lock);
+		wait_event(journal->j_wait_done_commit,
+				journal->j_task == NULL);
+		spin_lock(&journal->j_state_lock);
+	}
+	spin_unlock(&journal->j_state_lock);
+}
+
+/*
+ * journal_write_metadata_buffer: write a metadata buffer to the journal.
+ *
+ * Writes a metadata buffer to a given disk block.  The actual IO is not
+ * performed but a new buffer_head is constructed which labels the data
+ * to be written with the correct destination disk block.
+ *
+ * Any magic-number escaping which needs to be done will cause a
+ * copy-out here.  If the buffer happens to start with the
+ * JFS_MAGIC_NUMBER, then we can't write it to the log directly: the
+ * magic number is only written to the log for descripter blocks.  In
+ * this case, we copy the data and replace the first word with 0, and we
+ * return a result code which indicates that this buffer needs to be
+ * marked as an escaped buffer in the corresponding log descriptor
+ * block.  The missing word can then be restored when the block is read
+ * during recovery.
+ *
+ * If the source buffer has already been modified by a new transaction
+ * since we took the last commit snapshot, we use the frozen copy of
+ * that data for IO.  If we end up using the existing buffer_head's data
+ * for the write, then we *have* to lock the buffer to prevent anyone
+ * else from using and possibly modifying it while the IO is in
+ * progress.
+ *
+ * The function returns a pointer to the buffer_heads to be used for IO.
+ *
+ * We assume that the journal has already been locked in this function.
+ *
+ * Return value:
+ *  <0: Error
+ * >=0: Finished OK
+ *
+ * On success:
+ * Bit 0 set == escape performed on the data
+ * Bit 1 set == buffer copy-out performed (kfree the data after IO)
+ */
+
+int journal_write_metadata_buffer(transaction_t *transaction,
+				  struct journal_head  *jh_in,
+				  struct journal_head **jh_out,
+				  unsigned int 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);
+	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);
+	new_jh = journal_add_journal_head(new_bh);	/* This sleeps */
+
+	/*
+	 * If a new transaction has already done a buffer copy-out, then
+	 * we use that version of the data for the commit.
+	 */
+	jbd_lock_bh_state(bh_in);
+repeat:
+	if (jh_in->b_frozen_data) {
+		done_copy_out = 1;
+		new_page = virt_to_page(jh_in->b_frozen_data);
+		new_offset = offset_in_page(jh_in->b_frozen_data);
+	} else {
+		new_page = jh2bh(jh_in)->b_page;
+		new_offset = offset_in_page(jh2bh(jh_in)->b_data);
+	}
+
+	mapped_data = kmap_atomic(new_page);
+	/*
+	 * Check for escaping
+	 */
+	if (*((__be32 *)(mapped_data + new_offset)) ==
+				cpu_to_be32(JFS_MAGIC_NUMBER)) {
+		need_copy_out = 1;
+		do_escape = 1;
+	}
+	kunmap_atomic(mapped_data);
+
+	/*
+	 * Do we need to do a data copy?
+	 */
+	if (need_copy_out && !done_copy_out) {
+		char *tmp;
+
+		jbd_unlock_bh_state(bh_in);
+		tmp = jbd_alloc(bh_in->b_size, GFP_NOFS);
+		jbd_lock_bh_state(bh_in);
+		if (jh_in->b_frozen_data) {
+			jbd_free(tmp, bh_in->b_size);
+			goto repeat;
+		}
+
+		jh_in->b_frozen_data = tmp;
+		mapped_data = kmap_atomic(new_page);
+		memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
+		kunmap_atomic(mapped_data);
+
+		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);
+		*((unsigned int *)(mapped_data + new_offset)) = 0;
+		kunmap_atomic(mapped_data);
+	}
+
+	set_bh_page(new_bh, new_page, new_offset);
+	new_jh->b_transaction = NULL;
+	new_bh->b_size = jh2bh(jh_in)->b_size;
+	new_bh->b_bdev = transaction->t_journal->j_dev;
+	new_bh->b_blocknr = blocknr;
+	set_buffer_mapped(new_bh);
+	set_buffer_dirty(new_bh);
+
+	*jh_out = new_jh;
+
+	/*
+	 * The to-be-written buffer needs to get moved to the io queue,
+	 * and the original buffer whose contents we are shadowing or
+	 * copying is moved to the transaction's shadow queue.
+	 */
+	JBUFFER_TRACE(jh_in, "file as BJ_Shadow");
+	spin_lock(&journal->j_list_lock);
+	__journal_file_buffer(jh_in, transaction, BJ_Shadow);
+	spin_unlock(&journal->j_list_lock);
+	jbd_unlock_bh_state(bh_in);
+
+	JBUFFER_TRACE(new_jh, "file as BJ_IO");
+	journal_file_buffer(new_jh, transaction, BJ_IO);
+
+	return do_escape | (done_copy_out << 1);
+}
+
+/*
+ * Allocation code for the journal file.  Manage the space left in the
+ * journal, so that we can begin checkpointing when appropriate.
+ */
+
+/*
+ * __log_space_left: Return the number of free blocks left in the journal.
+ *
+ * Called with the journal already locked.
+ *
+ * Called under j_state_lock
+ */
+
+int __log_space_left(journal_t *journal)
+{
+	int left = journal->j_free;
+
+	assert_spin_locked(&journal->j_state_lock);
+
+	/*
+	 * Be pessimistic here about the number of those free blocks which
+	 * might be required for log descriptor control blocks.
+	 */
+
+#define MIN_LOG_RESERVED_BLOCKS 32 /* Allow for rounding errors */
+
+	left -= MIN_LOG_RESERVED_BLOCKS;
+
+	if (left <= 0)
+		return 0;
+	left -= (left >> 3);
+	return left;
+}
+
+/*
+ * Called under j_state_lock.  Returns true if a transaction commit was started.
+ */
+int __log_start_commit(journal_t *journal, tid_t target)
+{
+	/*
+	 * 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_commit_request != target &&
+	    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, "JBD: requesting commit %d/%d\n",
+			  journal->j_commit_request,
+			  journal->j_commit_sequence);
+		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, "jbd: 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 log_start_commit(journal_t *journal, tid_t tid)
+{
+	int ret;
+
+	spin_lock(&journal->j_state_lock);
+	ret = __log_start_commit(journal, tid);
+	spin_unlock(&journal->j_state_lock);
+	return ret;
+}
+
+/*
+ * Force and wait upon a commit if the calling process is not within
+ * transaction.  This is used for forcing out undo-protected data which contains
+ * bitmaps, when the fs is running out of space.
+ *
+ * We can only force the running transaction if we don't have an active handle;
+ * otherwise, we will deadlock.
+ *
+ * Returns true if a transaction was started.
+ */
+int journal_force_commit_nested(journal_t *journal)
+{
+	transaction_t *transaction = NULL;
+	tid_t tid;
+
+	spin_lock(&journal->j_state_lock);
+	if (journal->j_running_transaction && !current->journal_info) {
+		transaction = journal->j_running_transaction;
+		__log_start_commit(journal, transaction->t_tid);
+	} else if (journal->j_committing_transaction)
+		transaction = journal->j_committing_transaction;
+
+	if (!transaction) {
+		spin_unlock(&journal->j_state_lock);
+		return 0;	/* Nothing to retry */
+	}
+
+	tid = transaction->t_tid;
+	spin_unlock(&journal->j_state_lock);
+	log_wait_commit(journal, tid);
+	return 1;
+}
+
+/*
+ * Start a commit of the current running transaction (if any).  Returns true
+ * if a transaction is going to be committed (or is currently already
+ * committing), and fills its tid in at *ptid
+ */
+int journal_start_commit(journal_t *journal, tid_t *ptid)
+{
+	int ret = 0;
+
+	spin_lock(&journal->j_state_lock);
+	if (journal->j_running_transaction) {
+		tid_t tid = journal->j_running_transaction->t_tid;
+
+		__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;
+	}
+	spin_unlock(&journal->j_state_lock);
+	return ret;
+}
+
+/*
+ * Wait for a specified commit to complete.
+ * The caller may not hold the journal lock.
+ */
+int log_wait_commit(journal_t *journal, tid_t tid)
+{
+	int err = 0;
+
+#ifdef CONFIG_JBD_DEBUG
+	spin_lock(&journal->j_state_lock);
+	if (!tid_geq(journal->j_commit_request, tid)) {
+		printk(KERN_ERR
+		       "%s: error: j_commit_request=%d, tid=%d\n",
+		       __func__, journal->j_commit_request, tid);
+	}
+	spin_unlock(&journal->j_state_lock);
+#endif
+	spin_lock(&journal->j_state_lock);
+	/*
+	 * Not running or committing trans? Must be already committed. This
+	 * saves us from waiting for a *long* time when tid overflows.
+	 */
+	if (!((journal->j_running_transaction &&
+	       journal->j_running_transaction->t_tid == tid) ||
+	      (journal->j_committing_transaction &&
+	       journal->j_committing_transaction->t_tid == tid)))
+		goto out_unlock;
+
+	if (!tid_geq(journal->j_commit_waited, tid))
+		journal->j_commit_waited = tid;
+	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);
+	}
+out_unlock:
+	spin_unlock(&journal->j_state_lock);
+
+	if (unlikely(is_journal_aborted(journal)))
+		err = -EIO;
+	return err;
+}
+
+/*
+ * 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 journal_trans_will_send_data_barrier(journal_t *journal, tid_t tid)
+{
+	int ret = 0;
+	transaction_t *commit_trans;
+
+	if (!(journal->j_flags & JFS_BARRIER))
+		return 0;
+	spin_lock(&journal->j_state_lock);
+	/* Transaction already committed? */
+	if (tid_geq(journal->j_commit_sequence, tid))
+		goto out;
+	/*
+	 * Transaction is being committed and we already proceeded to
+	 * writing commit record?
+	 */
+	commit_trans = journal->j_committing_transaction;
+	if (commit_trans && commit_trans->t_tid == tid &&
+	    commit_trans->t_state >= T_COMMIT_RECORD)
+		goto out;
+	ret = 1;
+out:
+	spin_unlock(&journal->j_state_lock);
+	return ret;
+}
+EXPORT_SYMBOL(journal_trans_will_send_data_barrier);
+
+/*
+ * Log buffer allocation routines:
+ */
+
+int journal_next_log_block(journal_t *journal, unsigned int *retp)
+{
+	unsigned int blocknr;
+
+	spin_lock(&journal->j_state_lock);
+	J_ASSERT(journal->j_free > 1);
+
+	blocknr = journal->j_head;
+	journal->j_head++;
+	journal->j_free--;
+	if (journal->j_head == journal->j_last)
+		journal->j_head = journal->j_first;
+	spin_unlock(&journal->j_state_lock);
+	return journal_bmap(journal, blocknr, retp);
+}
+
+/*
+ * Conversion of logical to physical block numbers for the journal
+ *
+ * On external journals the journal blocks are identity-mapped, so
+ * this is a no-op.  If needed, we can use j_blk_offset - everything is
+ * ready.
+ */
+int journal_bmap(journal_t *journal, unsigned int blocknr,
+		 unsigned int *retp)
+{
+	int err = 0;
+	unsigned int 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 %u on %s\n",
+				__func__,
+				blocknr,
+				bdevname(journal->j_dev, b));
+			err = -EIO;
+			__journal_abort_soft(journal, err);
+		}
+	} else {
+		*retp = blocknr; /* +journal->j_blk_offset */
+	}
+	return err;
+}
+
+/*
+ * We play buffer_head aliasing tricks to write data/metadata blocks to
+ * the journal without copying their contents, but for journal
+ * descriptor blocks we do need to generate bona fide buffers.
+ *
+ * After the caller of journal_get_descriptor_buffer() has finished modifying
+ * the buffer's contents they really should run flush_dcache_page(bh->b_page).
+ * But we don't bother doing that, so there will be coherency problems with
+ * mmaps of blockdevs which hold live JBD-controlled filesystems.
+ */
+struct journal_head *journal_get_descriptor_buffer(journal_t *journal)
+{
+	struct buffer_head *bh;
+	unsigned int blocknr;
+	int err;
+
+	err = journal_next_log_block(journal, &blocknr);
+
+	if (err)
+		return NULL;
+
+	bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
+	if (!bh)
+		return NULL;
+	lock_buffer(bh);
+	memset(bh->b_data, 0, journal->j_blocksize);
+	set_buffer_uptodate(bh);
+	unlock_buffer(bh);
+	BUFFER_TRACE(bh, "return this buffer");
+	return journal_add_journal_head(bh);
+}
+
+/*
+ * Management for journal control blocks: functions to create and
+ * destroy journal_t structures, and to initialise and read existing
+ * journal blocks from disk.  */
+
+/* First: create and setup a journal_t object in memory.  We initialise
+ * very few fields yet: that has to wait until we have created the
+ * journal structures from from scratch, or loaded them from disk. */
+
+static journal_t * journal_init_common (void)
+{
+	journal_t *journal;
+	int err;
+
+	journal = kzalloc(sizeof(*journal), GFP_KERNEL);
+	if (!journal)
+		goto fail;
+
+	init_waitqueue_head(&journal->j_wait_transaction_locked);
+	init_waitqueue_head(&journal->j_wait_logspace);
+	init_waitqueue_head(&journal->j_wait_done_commit);
+	init_waitqueue_head(&journal->j_wait_checkpoint);
+	init_waitqueue_head(&journal->j_wait_commit);
+	init_waitqueue_head(&journal->j_wait_updates);
+	mutex_init(&journal->j_checkpoint_mutex);
+	spin_lock_init(&journal->j_revoke_lock);
+	spin_lock_init(&journal->j_list_lock);
+	spin_lock_init(&journal->j_state_lock);
+
+	journal->j_commit_interval = (HZ * JBD_DEFAULT_MAX_COMMIT_AGE);
+
+	/* The journal is marked for error until we succeed with recovery! */
+	journal->j_flags = JFS_ABORT;
+
+	/* Set up a default-sized revoke table for the new mount. */
+	err = journal_init_revoke(journal, JOURNAL_REVOKE_DEFAULT_HASH);
+	if (err) {
+		kfree(journal);
+		goto fail;
+	}
+	return journal;
+fail:
+	return NULL;
+}
+
+/* journal_init_dev and journal_init_inode:
+ *
+ * Create a journal structure assigned some fixed set of disk blocks to
+ * the journal.  We don't actually touch those disk blocks yet, but we
+ * need to set up all of the mapping information to tell the journaling
+ * system where the journal blocks are.
+ *
+ */
+
+/**
+ *  journal_t * journal_init_dev() - creates 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 *
+ *
+ *  journal_init_dev creates a journal which maps a fixed contiguous
+ *  range of blocks on an arbitrary block device.
+ *
+ */
+journal_t * journal_init_dev(struct block_device *bdev,
+			struct block_device *fs_dev,
+			int start, int len, int blocksize)
+{
+	journal_t *journal = journal_init_common();
+	struct buffer_head *bh;
+	int n;
+
+	if (!journal)
+		return NULL;
+
+	/* journal descriptor can store up to n blocks -bzzz */
+	journal->j_blocksize = blocksize;
+	n = journal->j_blocksize / sizeof(journal_block_tag_t);
+	journal->j_wbufsize = n;
+	journal->j_wbuf = kmalloc(n * sizeof(struct buffer_head*), GFP_KERNEL);
+	if (!journal->j_wbuf) {
+		printk(KERN_ERR "%s: Can't allocate bhs for commit thread\n",
+			__func__);
+		goto out_err;
+	}
+	journal->j_dev = bdev;
+	journal->j_fs_dev = fs_dev;
+	journal->j_blk_offset = start;
+	journal->j_maxlen = len;
+
+	bh = __getblk(journal->j_dev, start, journal->j_blocksize);
+	if (!bh) {
+		printk(KERN_ERR
+		       "%s: Cannot get buffer for journal superblock\n",
+		       __func__);
+		goto out_err;
+	}
+	journal->j_sb_buffer = bh;
+	journal->j_superblock = (journal_superblock_t *)bh->b_data;
+
+	return journal;
+out_err:
+	kfree(journal->j_wbuf);
+	kfree(journal);
+	return NULL;
+}
+
+/**
+ *  journal_t * journal_init_inode () - creates a journal which maps to a inode.
+ *  @inode: An inode to create the journal in
+ *
+ * journal_init_inode creates a journal which maps an on-disk inode as
+ * the journal.  The inode must exist already, must support bmap() and
+ * must have all data blocks preallocated.
+ */
+journal_t * journal_init_inode (struct inode *inode)
+{
+	struct buffer_head *bh;
+	journal_t *journal = journal_init_common();
+	int err;
+	int n;
+	unsigned int 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: Can't allocate bhs for commit thread\n",
+			__func__);
+		goto out_err;
+	}
+
+	err = journal_bmap(journal, 0, &blocknr);
+	/* If that failed, give up */
+	if (err) {
+		printk(KERN_ERR "%s: Cannot locate journal superblock\n",
+		       __func__);
+		goto out_err;
+	}
+
+	bh = getblk_unmovable(journal->j_dev, blocknr, journal->j_blocksize);
+	if (!bh) {
+		printk(KERN_ERR
+		       "%s: Cannot get buffer for journal superblock\n",
+		       __func__);
+		goto out_err;
+	}
+	journal->j_sb_buffer = bh;
+	journal->j_superblock = (journal_superblock_t *)bh->b_data;
+
+	return journal;
+out_err:
+	kfree(journal->j_wbuf);
+	kfree(journal);
+	return NULL;
+}
+
+/*
+ * If the journal init or create aborts, we need to mark the journal
+ * superblock as being NULL to prevent the journal destroy from writing
+ * back a bogus superblock.
+ */
+static void journal_fail_superblock (journal_t *journal)
+{
+	struct buffer_head *bh = journal->j_sb_buffer;
+	brelse(bh);
+	journal->j_sb_buffer = NULL;
+}
+
+/*
+ * Given a journal_t structure, initialise the various fields for
+ * startup of a new journaling session.  We use this both when creating
+ * a journal, and after recovering an old journal to reset it for
+ * subsequent use.
+ */
+
+static int journal_reset(journal_t *journal)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+	unsigned int first, last;
+
+	first = be32_to_cpu(sb->s_first);
+	last = be32_to_cpu(sb->s_maxlen);
+	if (first + JFS_MIN_JOURNAL_BLOCKS > last + 1) {
+		printk(KERN_ERR "JBD: Journal too short (blocks %u-%u).\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 JFS_FLUSHED.  This avoids
+	 * attempting a write to a potential-readonly device.
+	 */
+	if (sb->s_start == 0) {
+		jbd_debug(1,"JBD: Skipping superblock update on recovered sb "
+			"(start %u, seq %d, errno %d)\n",
+			journal->j_tail, journal->j_tail_sequence,
+			journal->j_errno);
+		journal->j_flags |= JFS_FLUSHED;
+	} else {
+		/* Lock here to make assertions happy... */
+		mutex_lock(&journal->j_checkpoint_mutex);
+		/*
+		 * Update log tail information. We use WRITE_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.
+		 */
+		journal_update_sb_log_tail(journal,
+					   journal->j_tail_sequence,
+					   journal->j_tail,
+					   WRITE_FUA);
+		mutex_unlock(&journal->j_checkpoint_mutex);
+	}
+	return journal_start_thread(journal);
+}
+
+/**
+ * int journal_create() - Initialise the new journal file
+ * @journal: Journal to create. This structure must have been initialised
+ *
+ * Given a journal_t structure which tells us which disk blocks we can
+ * use, create a new journal superblock and initialise all of the
+ * journal fields from scratch.
+ **/
+int journal_create(journal_t *journal)
+{
+	unsigned int blocknr;
+	struct buffer_head *bh;
+	journal_superblock_t *sb;
+	int i, err;
+
+	if (journal->j_maxlen < JFS_MIN_JOURNAL_BLOCKS) {
+		printk (KERN_ERR "Journal length (%d blocks) too short.\n",
+			journal->j_maxlen);
+		journal_fail_superblock(journal);
+		return -EINVAL;
+	}
+
+	if (journal->j_inode == NULL) {
+		/*
+		 * We don't know what block to start at!
+		 */
+		printk(KERN_EMERG
+		       "%s: creation of journal on external device!\n",
+		       __func__);
+		BUG();
+	}
+
+	/* Zero out the entire journal on disk.  We cannot afford to
+	   have any blocks on disk beginning with JFS_MAGIC_NUMBER. */
+	jbd_debug(1, "JBD: Zeroing out journal blocks...\n");
+	for (i = 0; i < journal->j_maxlen; i++) {
+		err = journal_bmap(journal, i, &blocknr);
+		if (err)
+			return err;
+		bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
+		if (unlikely(!bh))
+			return -ENOMEM;
+		lock_buffer(bh);
+		memset (bh->b_data, 0, journal->j_blocksize);
+		BUFFER_TRACE(bh, "marking dirty");
+		mark_buffer_dirty(bh);
+		BUFFER_TRACE(bh, "marking uptodate");
+		set_buffer_uptodate(bh);
+		unlock_buffer(bh);
+		__brelse(bh);
+	}
+
+	sync_blockdev(journal->j_dev);
+	jbd_debug(1, "JBD: journal cleared.\n");
+
+	/* OK, fill in the initial static fields in the new superblock */
+	sb = journal->j_superblock;
+
+	sb->s_header.h_magic	 = cpu_to_be32(JFS_MAGIC_NUMBER);
+	sb->s_header.h_blocktype = cpu_to_be32(JFS_SUPERBLOCK_V2);
+
+	sb->s_blocksize	= cpu_to_be32(journal->j_blocksize);
+	sb->s_maxlen	= cpu_to_be32(journal->j_maxlen);
+	sb->s_first	= cpu_to_be32(1);
+
+	journal->j_transaction_sequence = 1;
+
+	journal->j_flags &= ~JFS_ABORT;
+	journal->j_format_version = 2;
+
+	return journal_reset(journal);
+}
+
+static void journal_write_superblock(journal_t *journal, int write_op)
+{
+	struct buffer_head *bh = journal->j_sb_buffer;
+	int ret;
+
+	trace_journal_write_superblock(journal, write_op);
+	if (!(journal->j_flags & JFS_BARRIER))
+		write_op &= ~(REQ_FUA | REQ_FLUSH);
+	lock_buffer(bh);
+	if (buffer_write_io_error(bh)) {
+		char b[BDEVNAME_SIZE];
+		/*
+		 * 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 "JBD: previous I/O error detected "
+		       "for journal superblock update for %s.\n",
+		       journal_dev_name(journal, b));
+		clear_buffer_write_io_error(bh);
+		set_buffer_uptodate(bh);
+	}
+
+	get_bh(bh);
+	bh->b_end_io = end_buffer_write_sync;
+	ret = submit_bh(write_op, 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) {
+		char b[BDEVNAME_SIZE];
+		printk(KERN_ERR "JBD: Error %d detected "
+		       "when updating journal superblock for %s.\n",
+		       ret, journal_dev_name(journal, b));
+	}
+}
+
+/**
+ * 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.
+ */
+void journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
+				unsigned int tail_block, int write_op)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+
+	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
+	jbd_debug(1,"JBD: updating superblock (start %u, seq %u)\n",
+		  tail_block, tail_tid);
+
+	sb->s_sequence = cpu_to_be32(tail_tid);
+	sb->s_start    = cpu_to_be32(tail_block);
+
+	journal_write_superblock(journal, write_op);
+
+	/* Log is no longer empty */
+	spin_lock(&journal->j_state_lock);
+	WARN_ON(!sb->s_sequence);
+	journal->j_flags &= ~JFS_FLUSHED;
+	spin_unlock(&journal->j_state_lock);
+}
+
+/**
+ * mark_journal_empty() - Mark on disk journal as empty.
+ * @journal: The journal to update.
+ *
+ * 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 mark_journal_empty(journal_t *journal)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+
+	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
+	spin_lock(&journal->j_state_lock);
+	/* Is it already empty? */
+	if (sb->s_start == 0) {
+		spin_unlock(&journal->j_state_lock);
+		return;
+	}
+	jbd_debug(1, "JBD: Marking journal as empty (seq %d)\n",
+        	  journal->j_tail_sequence);
+
+	sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
+	sb->s_start    = cpu_to_be32(0);
+	spin_unlock(&journal->j_state_lock);
+
+	journal_write_superblock(journal, WRITE_FUA);
+
+	spin_lock(&journal->j_state_lock);
+	/* Log is empty */
+	journal->j_flags |= JFS_FLUSHED;
+	spin_unlock(&journal->j_state_lock);
+}
+
+/**
+ * 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.
+ */
+static void journal_update_sb_errno(journal_t *journal)
+{
+	journal_superblock_t *sb = journal->j_superblock;
+
+	spin_lock(&journal->j_state_lock);
+	jbd_debug(1, "JBD: updating superblock error (errno %d)\n",
+        	  journal->j_errno);
+	sb->s_errno = cpu_to_be32(journal->j_errno);
+	spin_unlock(&journal->j_state_lock);
+
+	journal_write_superblock(journal, WRITE_SYNC);
+}
+
+/*
+ * Read the superblock for a given journal, performing initial
+ * validation of the format.
+ */
+
+static int journal_get_superblock(journal_t *journal)
+{
+	struct buffer_head *bh;
+	journal_superblock_t *sb;
+	int err = -EIO;
+
+	bh = journal->j_sb_buffer;
+
+	J_ASSERT(bh != NULL);
+	if (!buffer_uptodate(bh)) {
+		ll_rw_block(READ, 1, &bh);
+		wait_on_buffer(bh);
+		if (!buffer_uptodate(bh)) {
+			printk (KERN_ERR
+				"JBD: IO error reading journal superblock\n");
+			goto out;
+		}
+	}
+
+	sb = journal->j_superblock;
+
+	err = -EINVAL;
+
+	if (sb->s_header.h_magic != cpu_to_be32(JFS_MAGIC_NUMBER) ||
+	    sb->s_blocksize != cpu_to_be32(journal->j_blocksize)) {
+		printk(KERN_WARNING "JBD: no valid journal superblock found\n");
+		goto out;
+	}
+
+	switch(be32_to_cpu(sb->s_header.h_blocktype)) {
+	case JFS_SUPERBLOCK_V1:
+		journal->j_format_version = 1;
+		break;
+	case JFS_SUPERBLOCK_V2:
+		journal->j_format_version = 2;
+		break;
+	default:
+		printk(KERN_WARNING "JBD: unrecognised superblock format ID\n");
+		goto out;
+	}
+
+	if (be32_to_cpu(sb->s_maxlen) < journal->j_maxlen)
+		journal->j_maxlen = be32_to_cpu(sb->s_maxlen);
+	else if (be32_to_cpu(sb->s_maxlen) > journal->j_maxlen) {
+		printk (KERN_WARNING "JBD: journal file too short\n");
+		goto out;
+	}
+
+	if (be32_to_cpu(sb->s_first) == 0 ||
+	    be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
+		printk(KERN_WARNING
+			"JBD: Invalid start block of journal: %u\n",
+			be32_to_cpu(sb->s_first));
+		goto out;
+	}
+
+	return 0;
+
+out:
+	journal_fail_superblock(journal);
+	return err;
+}
+
+/*
+ * Load the on-disk journal superblock and read the key fields into the
+ * journal_t.
+ */
+
+static int load_superblock(journal_t *journal)
+{
+	int err;
+	journal_superblock_t *sb;
+
+	err = journal_get_superblock(journal);
+	if (err)
+		return err;
+
+	sb = journal->j_superblock;
+
+	journal->j_tail_sequence = be32_to_cpu(sb->s_sequence);
+	journal->j_tail = be32_to_cpu(sb->s_start);
+	journal->j_first = be32_to_cpu(sb->s_first);
+	journal->j_last = be32_to_cpu(sb->s_maxlen);
+	journal->j_errno = be32_to_cpu(sb->s_errno);
+
+	return 0;
+}
+
+
+/**
+ * int journal_load() - Read journal from disk.
+ * @journal: Journal to act on.
+ *
+ * Given a journal_t structure which tells us which disk blocks contain
+ * a journal, read the journal from disk to initialise the in-memory
+ * structures.
+ */
+int journal_load(journal_t *journal)
+{
+	int err;
+	journal_superblock_t *sb;
+
+	err = load_superblock(journal);
+	if (err)
+		return err;
+
+	sb = journal->j_superblock;
+	/* If this is a V2 superblock, then we have to check the
+	 * features flags on it. */
+
+	if (journal->j_format_version >= 2) {
+		if ((sb->s_feature_ro_compat &
+		     ~cpu_to_be32(JFS_KNOWN_ROCOMPAT_FEATURES)) ||
+		    (sb->s_feature_incompat &
+		     ~cpu_to_be32(JFS_KNOWN_INCOMPAT_FEATURES))) {
+			printk (KERN_WARNING
+				"JBD: Unrecognised features on journal\n");
+			return -EINVAL;
+		}
+	}
+
+	/* Let the recovery code check whether it needs to recover any
+	 * data from the journal. */
+	if (journal_recover(journal))
+		goto recovery_error;
+
+	/* OK, we've finished with the dynamic journal bits:
+	 * reinitialise the dynamic contents of the superblock in memory
+	 * and reset them on disk. */
+	if (journal_reset(journal))
+		goto recovery_error;
+
+	journal->j_flags &= ~JFS_ABORT;
+	journal->j_flags |= JFS_LOADED;
+	return 0;
+
+recovery_error:
+	printk (KERN_WARNING "JBD: recovery failed\n");
+	return -EIO;
+}
+
+/**
+ * void journal_destroy() - Release a journal_t structure.
+ * @journal: Journal to act on.
+ *
+ * Release a journal_t structure once it is no longer in use by the
+ * journaled object.
+ * Return <0 if we couldn't clean up the journal.
+ */
+int 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)
+		journal_commit_transaction(journal);
+
+	/* Force any old transactions to disk */
+
+	/* We cannot race with anybody but must keep assertions happy */
+	mutex_lock(&journal->j_checkpoint_mutex);
+	/* Totally anal locking here... */
+	spin_lock(&journal->j_list_lock);
+	while (journal->j_checkpoint_transactions != NULL) {
+		spin_unlock(&journal->j_list_lock);
+		log_do_checkpoint(journal);
+		spin_lock(&journal->j_list_lock);
+	}
+
+	J_ASSERT(journal->j_running_transaction == NULL);
+	J_ASSERT(journal->j_committing_transaction == NULL);
+	J_ASSERT(journal->j_checkpoint_transactions == NULL);
+	spin_unlock(&journal->j_list_lock);
+
+	if (journal->j_sb_buffer) {
+		if (!is_journal_aborted(journal)) {
+			journal->j_tail_sequence =
+				++journal->j_transaction_sequence;
+			mark_journal_empty(journal);
+		} else
+			err = -EIO;
+		brelse(journal->j_sb_buffer);
+	}
+	mutex_unlock(&journal->j_checkpoint_mutex);
+
+	iput(journal->j_inode);
+	if (journal->j_revoke)
+		journal_destroy_revoke(journal);
+	kfree(journal->j_wbuf);
+	kfree(journal);
+
+	return err;
+}
+
+
+/**
+ *int journal_check_used_features () - Check if features specified are used.
+ * @journal: Journal to check.
+ * @compat: bitmask of compatible features
+ * @ro: bitmask of features that force read-only mount
+ * @incompat: bitmask of incompatible features
+ *
+ * Check whether the journal uses all of a given set of
+ * features.  Return true (non-zero) if it does.
+ **/
+
+int journal_check_used_features (journal_t *journal, unsigned long compat,
+				 unsigned long ro, unsigned long incompat)
+{
+	journal_superblock_t *sb;
+
+	if (!compat && !ro && !incompat)
+		return 1;
+	if (journal->j_format_version == 1)
+		return 0;
+
+	sb = journal->j_superblock;
+
+	if (((be32_to_cpu(sb->s_feature_compat) & compat) == compat) &&
+	    ((be32_to_cpu(sb->s_feature_ro_compat) & ro) == ro) &&
+	    ((be32_to_cpu(sb->s_feature_incompat) & incompat) == incompat))
+		return 1;
+
+	return 0;
+}
+
+/**
+ * int journal_check_available_features() - Check feature set in journalling layer
+ * @journal: Journal to check.
+ * @compat: bitmask of compatible features
+ * @ro: bitmask of features that force read-only mount
+ * @incompat: bitmask of incompatible features
+ *
+ * Check whether the journaling code supports the use of
+ * all of a given set of features on this journal.  Return true
+ * (non-zero) if it can. */
+
+int journal_check_available_features (journal_t *journal, unsigned long compat,
+				      unsigned long ro, unsigned long incompat)
+{
+	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   & JFS_KNOWN_COMPAT_FEATURES) == compat &&
+	    (ro       & JFS_KNOWN_ROCOMPAT_FEATURES) == ro &&
+	    (incompat & JFS_KNOWN_INCOMPAT_FEATURES) == incompat)
+		return 1;
+
+	return 0;
+}
+
+/**
+ * int journal_set_features () - Mark a given journal feature in the superblock
+ * @journal: Journal to act on.
+ * @compat: bitmask of compatible features
+ * @ro: bitmask of features that force read-only mount
+ * @incompat: bitmask of incompatible features
+ *
+ * Mark a given journal feature as present on the
+ * superblock.  Returns true if the requested features could be set.
+ *
+ */
+
+int journal_set_features (journal_t *journal, unsigned long compat,
+			  unsigned long ro, unsigned long incompat)
+{
+	journal_superblock_t *sb;
+
+	if (journal_check_used_features(journal, compat, ro, incompat))
+		return 1;
+
+	if (!journal_check_available_features(journal, compat, ro, incompat))
+		return 0;
+
+	jbd_debug(1, "Setting new features 0x%lx/0x%lx/0x%lx\n",
+		  compat, ro, incompat);
+
+	sb = journal->j_superblock;
+
+	sb->s_feature_compat    |= cpu_to_be32(compat);
+	sb->s_feature_ro_compat |= cpu_to_be32(ro);
+	sb->s_feature_incompat  |= cpu_to_be32(incompat);
+
+	return 1;
+}
+
+
+/**
+ * int journal_update_format () - Update on-disk journal structure.
+ * @journal: Journal to act on.
+ *
+ * Given an initialised but unloaded journal struct, poke about in the
+ * on-disk structure to update it to the most recent supported version.
+ */
+int journal_update_format (journal_t *journal)
+{
+	journal_superblock_t *sb;
+	int err;
+
+	err = journal_get_superblock(journal);
+	if (err)
+		return err;
+
+	sb = journal->j_superblock;
+
+	switch (be32_to_cpu(sb->s_header.h_blocktype)) {
+	case JFS_SUPERBLOCK_V2:
+		return 0;
+	case JFS_SUPERBLOCK_V1:
+		return journal_convert_superblock_v1(journal, sb);
+	default:
+		break;
+	}
+	return -EINVAL;
+}
+
+static int journal_convert_superblock_v1(journal_t *journal,
+					 journal_superblock_t *sb)
+{
+	int offset, blocksize;
+	struct buffer_head *bh;
+
+	printk(KERN_WARNING
+		"JBD: Converting superblock from version 1 to 2.\n");
+
+	/* Pre-initialise new fields to zero */
+	offset = ((char *) &(sb->s_feature_compat)) - ((char *) sb);
+	blocksize = be32_to_cpu(sb->s_blocksize);
+	memset(&sb->s_feature_compat, 0, blocksize-offset);
+
+	sb->s_nr_users = cpu_to_be32(1);
+	sb->s_header.h_blocktype = cpu_to_be32(JFS_SUPERBLOCK_V2);
+	journal->j_format_version = 2;
+
+	bh = journal->j_sb_buffer;
+	BUFFER_TRACE(bh, "marking dirty");
+	mark_buffer_dirty(bh);
+	sync_dirty_buffer(bh);
+	return 0;
+}
+
+
+/**
+ * int journal_flush () - Flush journal
+ * @journal: Journal to act on.
+ *
+ * Flush all data for a given journal to disk and empty the journal.
+ * Filesystems can use this when remounting readonly to ensure that
+ * recovery does not need to happen on remount.
+ */
+
+int journal_flush(journal_t *journal)
+{
+	int err = 0;
+	transaction_t *transaction = NULL;
+
+	spin_lock(&journal->j_state_lock);
+
+	/* Force everything buffered to the log... */
+	if (journal->j_running_transaction) {
+		transaction = journal->j_running_transaction;
+		__log_start_commit(journal, transaction->t_tid);
+	} else if (journal->j_committing_transaction)
+		transaction = journal->j_committing_transaction;
+
+	/* Wait for the log commit to complete... */
+	if (transaction) {
+		tid_t tid = transaction->t_tid;
+
+		spin_unlock(&journal->j_state_lock);
+		log_wait_commit(journal, tid);
+	} else {
+		spin_unlock(&journal->j_state_lock);
+	}
+
+	/* ...and flush everything in the log out to disk. */
+	spin_lock(&journal->j_list_lock);
+	while (!err && journal->j_checkpoint_transactions != NULL) {
+		spin_unlock(&journal->j_list_lock);
+		mutex_lock(&journal->j_checkpoint_mutex);
+		err = 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(&journal->j_checkpoint_mutex);
+	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. */
+	mark_journal_empty(journal);
+	mutex_unlock(&journal->j_checkpoint_mutex);
+	spin_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);
+	spin_unlock(&journal->j_state_lock);
+	return 0;
+}
+
+/**
+ * int journal_wipe() - Wipe journal contents
+ * @journal: Journal to act on.
+ * @write: flag (see below)
+ *
+ * Wipe out all of the contents of a journal, safely.  This will produce
+ * a warning if the journal contains any valid recovery information.
+ * Must be called between journal_init_*() and journal_load().
+ *
+ * If 'write' is non-zero, then we wipe out the journal on disk; otherwise
+ * we merely suppress recovery.
+ */
+
+int journal_wipe(journal_t *journal, int write)
+{
+	int err = 0;
+
+	J_ASSERT (!(journal->j_flags & JFS_LOADED));
+
+	err = load_superblock(journal);
+	if (err)
+		return err;
+
+	if (!journal->j_tail)
+		goto no_recovery;
+
+	printk (KERN_WARNING "JBD: %s recovery information on journal\n",
+		write ? "Clearing" : "Ignoring");
+
+	err = journal_skip_recovery(journal);
+	if (write) {
+		/* Lock to make assertions happy... */
+		mutex_lock(&journal->j_checkpoint_mutex);
+		mark_journal_empty(journal);
+		mutex_unlock(&journal->j_checkpoint_mutex);
+	}
+
+ no_recovery:
+	return err;
+}
+
+/*
+ * journal_dev_name: format a character string to describe on what
+ * device this journal is present.
+ */
+
+static const char *journal_dev_name(journal_t *journal, char *buffer)
+{
+	struct block_device *bdev;
+
+	if (journal->j_inode)
+		bdev = journal->j_inode->i_sb->s_bdev;
+	else
+		bdev = journal->j_dev;
+
+	return bdevname(bdev, buffer);
+}
+
+/*
+ * Journal abort has very specific semantics, which we describe
+ * for journal abort.
+ *
+ * Two internal function, which provide abort to te jbd layer
+ * itself are here.
+ */
+
+/*
+ * Quick version for internal journal use (doesn't lock the journal).
+ * Aborts hard --- we mark the abort as occurred, but do _nothing_ else,
+ * and don't attempt to make any other journal updates.
+ */
+static void __journal_abort_hard(journal_t *journal)
+{
+	transaction_t *transaction;
+	char b[BDEVNAME_SIZE];
+
+	if (journal->j_flags & JFS_ABORT)
+		return;
+
+	printk(KERN_ERR "Aborting journal on device %s.\n",
+		journal_dev_name(journal, b));
+
+	spin_lock(&journal->j_state_lock);
+	journal->j_flags |= JFS_ABORT;
+	transaction = journal->j_running_transaction;
+	if (transaction)
+		__log_start_commit(journal, transaction->t_tid);
+	spin_unlock(&journal->j_state_lock);
+}
+
+/* Soft abort: record the abort error status in the journal superblock,
+ * but don't do any other IO. */
+static void __journal_abort_soft (journal_t *journal, int errno)
+{
+	if (journal->j_flags & JFS_ABORT)
+		return;
+
+	if (!journal->j_errno)
+		journal->j_errno = errno;
+
+	__journal_abort_hard(journal);
+
+	if (errno)
+		journal_update_sb_errno(journal);
+}
+
+/**
+ * void journal_abort () - Shutdown the journal immediately.
+ * @journal: the journal to shutdown.
+ * @errno:   an error number to record in the journal indicating
+ *           the reason for the shutdown.
+ *
+ * Perform a complete, immediate shutdown of the ENTIRE
+ * journal (not of a single transaction).  This operation cannot be
+ * undone without closing and reopening the journal.
+ *
+ * The journal_abort function is intended to support higher level error
+ * recovery mechanisms such as the ext2/ext3 remount-readonly error
+ * mode.
+ *
+ * Journal abort has very specific semantics.  Any existing dirty,
+ * unjournaled buffers in the main filesystem will still be written to
+ * disk by bdflush, but the journaling mechanism will be suspended
+ * immediately and no further transaction commits will be honoured.
+ *
+ * Any dirty, journaled buffers will be written back to disk without
+ * hitting the journal.  Atomicity cannot be guaranteed on an aborted
+ * filesystem, but we _do_ attempt to leave as much data as possible
+ * behind for fsck to use for cleanup.
+ *
+ * Any attempt to get a new transaction handle on a journal which is in
+ * ABORT state will just result in an -EROFS error return.  A
+ * journal_stop on an existing handle will return -EIO if we have
+ * entered abort state during the update.
+ *
+ * Recursive transactions are not disturbed by journal abort until the
+ * final journal_stop, which will receive the -EIO error.
+ *
+ * Finally, the journal_abort call allows the caller to supply an errno
+ * which will be recorded (if possible) in the journal superblock.  This
+ * allows a client to record failure conditions in the middle of a
+ * transaction without having to complete the transaction to record the
+ * failure to disk.  ext3_error, for example, now uses this
+ * functionality.
+ *
+ * Errors which originate from within the journaling layer will NOT
+ * supply an errno; a null errno implies that absolutely no further
+ * writes are done to the journal (unless there are any already in
+ * progress).
+ *
+ */
+
+void journal_abort(journal_t *journal, int errno)
+{
+	__journal_abort_soft(journal, errno);
+}
+
+/**
+ * int journal_errno () - returns the journal's error state.
+ * @journal: journal to examine.
+ *
+ * This is the errno numbet set with journal_abort(), the last
+ * time the journal was mounted - if the journal was stopped
+ * without calling abort this will be 0.
+ *
+ * If the journal has been aborted on this mount time -EROFS will
+ * be returned.
+ */
+int journal_errno(journal_t *journal)
+{
+	int err;
+
+	spin_lock(&journal->j_state_lock);
+	if (journal->j_flags & JFS_ABORT)
+		err = -EROFS;
+	else
+		err = journal->j_errno;
+	spin_unlock(&journal->j_state_lock);
+	return err;
+}
+
+/**
+ * int journal_clear_err () - clears the journal's error state
+ * @journal: journal to act on.
+ *
+ * An error must be cleared or Acked to take a FS out of readonly
+ * mode.
+ */
+int journal_clear_err(journal_t *journal)
+{
+	int err = 0;
+
+	spin_lock(&journal->j_state_lock);
+	if (journal->j_flags & JFS_ABORT)
+		err = -EROFS;
+	else
+		journal->j_errno = 0;
+	spin_unlock(&journal->j_state_lock);
+	return err;
+}
+
+/**
+ * void journal_ack_err() - Ack journal err.
+ * @journal: journal to act on.
+ *
+ * An error must be cleared or Acked to take a FS out of readonly
+ * mode.
+ */
+void journal_ack_err(journal_t *journal)
+{
+	spin_lock(&journal->j_state_lock);
+	if (journal->j_errno)
+		journal->j_flags |= JFS_ACK_ERR;
+	spin_unlock(&journal->j_state_lock);
+}
+
+int journal_blocks_per_page(struct inode *inode)
+{
+	return 1 << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
+}
+
+/*
+ * Journal_head storage management
+ */
+static struct kmem_cache *journal_head_cache;
+#ifdef CONFIG_JBD_DEBUG
+static atomic_t nr_journal_heads = ATOMIC_INIT(0);
+#endif
+
+static int journal_init_journal_head_cache(void)
+{
+	int retval;
+
+	J_ASSERT(journal_head_cache == NULL);
+	journal_head_cache = kmem_cache_create("journal_head",
+				sizeof(struct journal_head),
+				0,		/* offset */
+				SLAB_TEMPORARY,	/* flags */
+				NULL);		/* ctor */
+	retval = 0;
+	if (!journal_head_cache) {
+		retval = -ENOMEM;
+		printk(KERN_EMERG "JBD: no memory for journal_head cache\n");
+	}
+	return retval;
+}
+
+static void journal_destroy_journal_head_cache(void)
+{
+	if (journal_head_cache) {
+		kmem_cache_destroy(journal_head_cache);
+		journal_head_cache = NULL;
+	}
+}
+
+/*
+ * journal_head splicing and dicing
+ */
+static struct journal_head *journal_alloc_journal_head(void)
+{
+	struct journal_head *ret;
+
+#ifdef CONFIG_JBD_DEBUG
+	atomic_inc(&nr_journal_heads);
+#endif
+	ret = kmem_cache_zalloc(journal_head_cache, GFP_NOFS);
+	if (ret == NULL) {
+		jbd_debug(1, "out of memory for journal_head\n");
+		printk_ratelimited(KERN_NOTICE "ENOMEM in %s, retrying.\n",
+				   __func__);
+
+		while (ret == NULL) {
+			yield();
+			ret = kmem_cache_zalloc(journal_head_cache, GFP_NOFS);
+		}
+	}
+	return ret;
+}
+
+static void journal_free_journal_head(struct journal_head *jh)
+{
+#ifdef CONFIG_JBD_DEBUG
+	atomic_dec(&nr_journal_heads);
+	memset(jh, JBD_POISON_FREE, sizeof(*jh));
+#endif
+	kmem_cache_free(journal_head_cache, jh);
+}
+
+/*
+ * A journal_head is attached to a buffer_head whenever JBD has an
+ * interest in the buffer.
+ *
+ * Whenever a buffer has an attached journal_head, its ->b_state:BH_JBD bit
+ * is set.  This bit is tested in core kernel code where we need to take
+ * JBD-specific actions.  Testing the zeroness of ->b_private is not reliable
+ * there.
+ *
+ * When a buffer has its BH_JBD bit set, its ->b_count is elevated by one.
+ *
+ * When a buffer has its BH_JBD bit set it is immune from being released by
+ * core kernel code, mainly via ->b_count.
+ *
+ * A journal_head 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, journal_add_journal_head elevates the
+ * journal_head's b_jcount refcount by one.  The caller must call
+ * journal_put_journal_head() to undo this.
+ *
+ * So the typical usage would be:
+ *
+ *	(Attach a journal_head if needed.  Increments b_jcount)
+ *	struct journal_head *jh = journal_add_journal_head(bh);
+ *	...
+ *      (Get another reference for transaction)
+ *      journal_grab_journal_head(bh);
+ *      jh->b_transaction = xxx;
+ *      (Put original reference)
+ *      journal_put_journal_head(jh);
+ */
+
+/*
+ * Give a buffer_head a journal_head.
+ *
+ * May sleep.
+ */
+struct journal_head *journal_add_journal_head(struct buffer_head *bh)
+{
+	struct journal_head *jh;
+	struct journal_head *new_jh = NULL;
+
+repeat:
+	if (!buffer_jbd(bh))
+		new_jh = journal_alloc_journal_head();
+
+	jbd_lock_bh_journal_head(bh);
+	if (buffer_jbd(bh)) {
+		jh = bh2jh(bh);
+	} else {
+		J_ASSERT_BH(bh,
+			(atomic_read(&bh->b_count) > 0) ||
+			(bh->b_page && bh->b_page->mapping));
+
+		if (!new_jh) {
+			jbd_unlock_bh_journal_head(bh);
+			goto repeat;
+		}
+
+		jh = new_jh;
+		new_jh = NULL;		/* We consumed it */
+		set_buffer_jbd(bh);
+		bh->b_private = jh;
+		jh->b_bh = bh;
+		get_bh(bh);
+		BUFFER_TRACE(bh, "added journal_head");
+	}
+	jh->b_jcount++;
+	jbd_unlock_bh_journal_head(bh);
+	if (new_jh)
+		journal_free_journal_head(new_jh);
+	return bh->b_private;
+}
+
+/*
+ * Grab a ref against this buffer_head's journal_head.  If it ended up not
+ * having a journal_head, return NULL
+ */
+struct journal_head *journal_grab_journal_head(struct buffer_head *bh)
+{
+	struct journal_head *jh = NULL;
+
+	jbd_lock_bh_journal_head(bh);
+	if (buffer_jbd(bh)) {
+		jh = bh2jh(bh);
+		jh->b_jcount++;
+	}
+	jbd_unlock_bh_journal_head(bh);
+	return jh;
+}
+
+static void __journal_remove_journal_head(struct buffer_head *bh)
+{
+	struct journal_head *jh = bh2jh(bh);
+
+	J_ASSERT_JH(jh, jh->b_jcount >= 0);
+	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__);
+		jbd_free(jh->b_frozen_data, bh->b_size);
+	}
+	if (jh->b_committed_data) {
+		printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
+		jbd_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 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);
+}
+
+/*
+ * debugfs tunables
+ */
+#ifdef CONFIG_JBD_DEBUG
+
+u8 journal_enable_debug __read_mostly;
+EXPORT_SYMBOL(journal_enable_debug);
+
+static struct dentry *jbd_debugfs_dir;
+static struct dentry *jbd_debug;
+
+static void __init jbd_create_debugfs_entry(void)
+{
+	jbd_debugfs_dir = debugfs_create_dir("jbd", NULL);
+	if (jbd_debugfs_dir)
+		jbd_debug = debugfs_create_u8("jbd-debug", S_IRUGO | S_IWUSR,
+					       jbd_debugfs_dir,
+					       &journal_enable_debug);
+}
+
+static void __exit jbd_remove_debugfs_entry(void)
+{
+	debugfs_remove(jbd_debug);
+	debugfs_remove(jbd_debugfs_dir);
+}
+
+#else
+
+static inline void jbd_create_debugfs_entry(void)
+{
+}
+
+static inline void jbd_remove_debugfs_entry(void)
+{
+}
+
+#endif
+
+struct kmem_cache *jbd_handle_cache;
+
+static int __init journal_init_handle_cache(void)
+{
+	jbd_handle_cache = kmem_cache_create("journal_handle",
+				sizeof(handle_t),
+				0,		/* offset */
+				SLAB_TEMPORARY,	/* flags */
+				NULL);		/* ctor */
+	if (jbd_handle_cache == NULL) {
+		printk(KERN_EMERG "JBD: failed to create handle cache\n");
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+static void journal_destroy_handle_cache(void)
+{
+	if (jbd_handle_cache)
+		kmem_cache_destroy(jbd_handle_cache);
+}
+
+/*
+ * Module startup and shutdown
+ */
+
+static int __init journal_init_caches(void)
+{
+	int ret;
+
+	ret = journal_init_revoke_caches();
+	if (ret == 0)
+		ret = journal_init_journal_head_cache();
+	if (ret == 0)
+		ret = journal_init_handle_cache();
+	return ret;
+}
+
+static void journal_destroy_caches(void)
+{
+	journal_destroy_revoke_caches();
+	journal_destroy_journal_head_cache();
+	journal_destroy_handle_cache();
+}
+
+static int __init journal_init(void)
+{
+	int ret;
+
+	BUILD_BUG_ON(sizeof(struct journal_superblock_s) != 1024);
+
+	ret = journal_init_caches();
+	if (ret != 0)
+		journal_destroy_caches();
+	jbd_create_debugfs_entry();
+	return ret;
+}
+
+static void __exit journal_exit(void)
+{
+#ifdef CONFIG_JBD_DEBUG
+	int n = atomic_read(&nr_journal_heads);
+	if (n)
+		printk(KERN_ERR "JBD: leaked %d journal_heads!\n", n);
+#endif
+	jbd_remove_debugfs_entry();
+	journal_destroy_caches();
+}
+
+MODULE_LICENSE("GPL");
+module_init(journal_init);
+module_exit(journal_exit);
+