journal.c

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	if (wait)
		wait_on_buffer(bh);

	/* If we have just flushed the log (by marking s_start==0), then
	 * any future commit will have to be careful to update the
	 * superblock again to re-record the true start of the log. */

	if (sb->s_start)
		journal->j_flags &= ~JFS_FLUSHED;
	else
		journal->j_flags |= JFS_FLUSHED;
}


/*
 * 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 != htonl(JFS_MAGIC_NUMBER) ||
	    sb->s_blocksize != htonl(journal->j_blocksize)) {
		printk(KERN_WARNING "JBD: no valid journal superblock found\n");
		goto out;
	}

	switch(ntohl(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 (ntohl(sb->s_maxlen) < journal->j_maxlen)
		journal->j_maxlen = ntohl(sb->s_maxlen);
	else if (ntohl(sb->s_maxlen) > journal->j_maxlen) {
		printk (KERN_WARNING "JBD: journal file too short\n");
		goto out;
	}

	return 0;

out:
	journal_fail_superblock(journal);
	return err;
}

/*
 * Load the on-disk journal superblock and read the key fields into the
 * journal_t.
 */

static int load_superblock(journal_t *journal)
{
	int err;
	journal_superblock_t *sb;

	err = journal_get_superblock(journal);
	if (err)
		return err;

	sb = journal->j_superblock;

	journal->j_tail_sequence = ntohl(sb->s_sequence);
	journal->j_tail = ntohl(sb->s_start);
	journal->j_first = ntohl(sb->s_first);
	journal->j_last = ntohl(sb->s_maxlen);
	journal->j_errno = ntohl(sb->s_errno);

	return 0;
}


/*
 * 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;

	err = load_superblock(journal);
	if (err)
		return err;

	/* If this is a V2 superblock, then we have to check the
	 * features flags on it. */

	if (journal->j_format_version >= 2) {
		journal_superblock_t *sb = journal->j_superblock;

		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;
}

/*
 * Release a journal_t structure once it is no longer in use by the
 * journaled object.
 */

void journal_destroy (journal_t *journal)
{
	/* Wait for the commit thread to wake up and die. */
	journal_kill_thread(journal);

	/* Force a final log commit */
	if (journal->j_running_transaction)
		journal_commit_transaction(journal);

	/* Force any old transactions to disk */
	lock_journal(journal);
	while (journal->j_checkpoint_transactions != NULL)
		log_do_checkpoint(journal, 1);

	J_ASSERT(journal->j_running_transaction == NULL);
	J_ASSERT(journal->j_committing_transaction == NULL);
	J_ASSERT(journal->j_checkpoint_transactions == NULL);

	/* We can now mark the journal as empty. */
	journal->j_tail = 0;
	journal->j_tail_sequence = ++journal->j_transaction_sequence;
	if (journal->j_sb_buffer) {
		journal_update_superblock(journal, 1);
		brelse(journal->j_sb_buffer);
	}

	if (journal->j_inode)
		iput(journal->j_inode);
	if (journal->j_revoke)
		journal_destroy_revoke(journal);

	unlock_journal(journal);
	kfree(journal);
	MOD_DEC_USE_COUNT;
}


/* Published API: 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;
}

/* Published API: Check whether the journaling code supports the use of
 * all of a given set of features on this journal.  Return true
 * (non-zero) if it can. */

int journal_check_available_features (journal_t *journal, unsigned long compat,
				      unsigned long ro, unsigned long incompat)
{
	journal_superblock_t *sb;

	if (!compat && !ro && !incompat)
		return 1;

	sb = journal->j_superblock;

	/* We can support any known requested features iff the
	 * superblock is in version 2.  Otherwise we fail to support any
	 * extended sb features. */

	if (journal->j_format_version != 2)
		return 0;

	if ((compat   & JFS_KNOWN_COMPAT_FEATURES) == compat &&
	    (ro       & JFS_KNOWN_ROCOMPAT_FEATURES) == ro &&
	    (incompat & JFS_KNOWN_INCOMPAT_FEATURES) == incompat)
		return 1;

	return 0;
}

/* Published API: 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;
}


/*
 * Published API:
 * 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 (ntohl(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 = ntohl(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);
	ll_rw_block(WRITE, 1, &bh);
	wait_on_buffer(bh);
	return 0;
}


/*
 * Flush all data for a given journal to disk and empty the journal.
 * Filesystems can use this when remounting readonly to ensure that
 * recovery does not need to happen on remount.
 */

int journal_flush (journal_t *journal)
{
	int err = 0;
	transaction_t *transaction = NULL;
	unsigned long old_tail;

	lock_kernel();
	
	/* Force everything buffered to the log... */
	if (journal->j_running_transaction) {
		transaction = journal->j_running_transaction;
		log_start_commit(journal, transaction);
	} else if (journal->j_committing_transaction)
		transaction = journal->j_committing_transaction;

	/* Wait for the log commit to complete... */
	if (transaction)
		log_wait_commit(journal, transaction->t_tid);

	/* ...and flush everything in the log out to disk. */
	lock_journal(journal);
	while (!err && journal->j_checkpoint_transactions != NULL)
		err = log_do_checkpoint(journal, journal->j_maxlen);
	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. */
	old_tail = journal->j_tail;
	journal->j_tail = 0;
	journal_update_superblock(journal, 1);
	journal->j_tail = old_tail;

	unlock_journal(journal);

	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);

	unlock_kernel();
	
	return err;
}

/*
 * Wipe out all of the contents of a journal, safely.  This will produce
 * a warning if the journal contains any valid recovery information.
 * Must be called between journal_init_*() and journal_load().
 *
 * If (write) is non-zero, then we wipe out the journal on disk; otherwise
 * we merely suppress recovery.
 */

int journal_wipe (journal_t *journal, int write)
{
	journal_superblock_t *sb;
	int err = 0;

	J_ASSERT (!(journal->j_flags & JFS_LOADED));

	err = load_superblock(journal);
	if (err)
		return err;

	sb = journal->j_superblock;

	if (!journal->j_tail)
		goto no_recovery;

	printk (KERN_WARNING "JBD: %s recovery information on journal\n",
		write ? "Clearing" : "Ignoring");

	err = journal_skip_recovery(journal);
	if (write)
		journal_update_superblock(journal, 1);

 no_recovery:
	return err;
}

/*
 * journal_dev_name: format a character string to describe on what
 * device this journal is present.
 */

const char * journal_dev_name(journal_t *journal)
{
	kdev_t dev;

	if (journal->j_inode)
		dev = journal->j_inode->i_dev;
	else
		dev = journal->j_dev;

	return bdevname(dev);
}

/*
 * journal_abort: 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 recored (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