fs/ocfs2/buffer_head_io.c - kernel/msm-4.9 - Gitiles

 /* -*- mode: c; c-basic-offset: 8; -*-
  * vim: noexpandtab sw=8 ts=8 sts=0:
  *
  * io.c
  *
  * Buffer cache handling
  *
  * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  *
  * You should have received a copy of the GNU General Public
  * License along with this program; if not, write to the
  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  * Boston, MA 021110-1307, USA.
  */

 #include <linux/fs.h>
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/highmem.h>

 #include <cluster/masklog.h>

 #include "ocfs2.h"

 #include "alloc.h"
 #include "inode.h"
 #include "journal.h"
 #include "uptodate.h"

 #include "buffer_head_io.h"

 int ocfs2_write_block(struct ocfs2_super *osb, struct buffer_head *bh,
 		      struct inode *inode)
 {
 	int ret = 0;

 	mlog_entry("(bh->b_blocknr = %llu, inode=%p)\n",
 		   (unsigned long long)bh->b_blocknr, inode);

 	BUG_ON(bh->b_blocknr < OCFS2_SUPER_BLOCK_BLKNO);
 	BUG_ON(buffer_jbd(bh));

 	/* No need to check for a soft readonly file system here. non
 	 * journalled writes are only ever done on system files which
 	 * can get modified during recovery even if read-only. */
 	if (ocfs2_is_hard_readonly(osb)) {
 		ret = -EROFS;
 		goto out;
 	}

 	mutex_lock(&OCFS2_I(inode)->ip_io_mutex);

 	lock_buffer(bh);
 	set_buffer_uptodate(bh);

 	/* remove from dirty list before I/O. */
 	clear_buffer_dirty(bh);

 	get_bh(bh); /* for end_buffer_write_sync() */
 	bh->b_end_io = end_buffer_write_sync;
 	submit_bh(WRITE, bh);

 	wait_on_buffer(bh);

 	if (buffer_uptodate(bh)) {
 		ocfs2_set_buffer_uptodate(inode, bh);
 	} else {
 		/* We don't need to remove the clustered uptodate
 		 * information for this bh as it's not marked locally
 		 * uptodate. */
 		ret = -EIO;
 		put_bh(bh);
 	}

 	mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);
 out:
 	mlog_exit(ret);
 	return ret;
 }

 int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
 			   unsigned int nr, struct buffer_head *bhs[])
 {
 	int status = 0;
 	unsigned int i;
 	struct buffer_head *bh;

 	if (!nr) {
 		mlog(ML_BH_IO, "No buffers will be read!\n");
 		goto bail;
 	}

 	for (i = 0 ; i < nr ; i++) {
 		if (bhs[i] == NULL) {
 			bhs[i] = sb_getblk(osb->sb, block++);
 			if (bhs[i] == NULL) {
 				status = -EIO;
 				mlog_errno(status);
 				goto bail;
 			}
 		}
 		bh = bhs[i];

 		if (buffer_jbd(bh)) {
 			mlog(ML_ERROR,
 			     "trying to sync read a jbd "
 			     "managed bh (blocknr = %llu), skipping\n",
 			     (unsigned long long)bh->b_blocknr);
 			continue;
 		}

 		if (buffer_dirty(bh)) {
 			/* This should probably be a BUG, or
 			 * at least return an error. */
 			mlog(ML_ERROR,
 			     "trying to sync read a dirty "
 			     "buffer! (blocknr = %llu), skipping\n",
 			     (unsigned long long)bh->b_blocknr);
 			continue;
 		}

 		lock_buffer(bh);
 		if (buffer_jbd(bh)) {
 			mlog(ML_ERROR,
 			     "block %llu had the JBD bit set "
 			     "while I was in lock_buffer!",
 			     (unsigned long long)bh->b_blocknr);
 			BUG();
 		}

 		clear_buffer_uptodate(bh);
 		get_bh(bh); /* for end_buffer_read_sync() */
 		bh->b_end_io = end_buffer_read_sync;
 		submit_bh(READ, bh);
 	}

 	for (i = nr; i > 0; i--) {
 		bh = bhs[i - 1];

 		if (buffer_jbd(bh)) {
 			mlog(ML_ERROR,
 			     "the journal got the buffer while it was "
 			     "locked for io! (blocknr = %llu)\n",
 			     (unsigned long long)bh->b_blocknr);
 			BUG();
 		}

 		wait_on_buffer(bh);
 		if (!buffer_uptodate(bh)) {
 			/* Status won't be cleared from here on out,
 			 * so we can safely record this and loop back
 			 * to cleanup the other buffers. */
 			status = -EIO;
 			put_bh(bh);
 			bhs[i - 1] = NULL;
 		}
 	}

 bail:
 	return status;
 }

 int ocfs2_read_blocks(struct inode *inode, u64 block, int nr,
 		      struct buffer_head *bhs[], int flags)
 {
 	int status = 0;
 	int i, ignore_cache = 0;
 	struct buffer_head *bh;

 	mlog_entry("(inode=%p, block=(%llu), nr=(%d), flags=%d)\n",
 		   inode, (unsigned long long)block, nr, flags);

 	BUG_ON(!inode);
 	BUG_ON((flags & OCFS2_BH_READAHEAD) &&
 	       (flags & OCFS2_BH_IGNORE_CACHE));

 	if (bhs == NULL) {
 		status = -EINVAL;
 		mlog_errno(status);
 		goto bail;
 	}

 	if (nr < 0) {
 		mlog(ML_ERROR, "asked to read %d blocks!\n", nr);
 		status = -EINVAL;
 		mlog_errno(status);
 		goto bail;
 	}

 	if (nr == 0) {
 		mlog(ML_BH_IO, "No buffers will be read!\n");
 		status = 0;
 		goto bail;
 	}

 	mutex_lock(&OCFS2_I(inode)->ip_io_mutex);
 	for (i = 0 ; i < nr ; i++) {
 		if (bhs[i] == NULL) {
 			bhs[i] = sb_getblk(inode->i_sb, block++);
 			if (bhs[i] == NULL) {
 				mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);
 				status = -EIO;
 				mlog_errno(status);
 				goto bail;
 			}
 		}
 		bh = bhs[i];
 		ignore_cache = (flags & OCFS2_BH_IGNORE_CACHE);

 		/* There are three read-ahead cases here which we need to
 		 * be concerned with. All three assume a buffer has
 		 * previously been submitted with OCFS2_BH_READAHEAD
 		 * and it hasn't yet completed I/O.
 		 *
 		 * 1) The current request is sync to disk. This rarely
 		 *    happens these days, and never when performance
 		 *    matters - the code can just wait on the buffer
 		 *    lock and re-submit.
 		 *
 		 * 2) The current request is cached, but not
 		 *    readahead. ocfs2_buffer_uptodate() will return
 		 *    false anyway, so we'll wind up waiting on the
 		 *    buffer lock to do I/O. We re-check the request
 		 *    with after getting the lock to avoid a re-submit.
 		 *
 		 * 3) The current request is readahead (and so must
 		 *    also be a caching one). We short circuit if the
 		 *    buffer is locked (under I/O) and if it's in the
 		 *    uptodate cache. The re-check from #2 catches the
 		 *    case that the previous read-ahead completes just
 		 *    before our is-it-in-flight check.
 		 */

 		if (!ignore_cache && !ocfs2_buffer_uptodate(inode, bh)) {
 			mlog(ML_UPTODATE,
 			     "bh (%llu), inode %llu not uptodate\n",
 			     (unsigned long long)bh->b_blocknr,
 			     (unsigned long long)OCFS2_I(inode)->ip_blkno);
 			/* We're using ignore_cache here to say
 			 * "go to disk" */
 			ignore_cache = 1;
 		}

 		/* XXX: Can we ever get this and *not* have the cached
 		 * flag set? */
 		if (buffer_jbd(bh)) {
 			if (ignore_cache)
 				mlog(ML_BH_IO, "trying to sync read a jbd "
 					       "managed bh (blocknr = %llu)\n",
 				     (unsigned long long)bh->b_blocknr);
 			continue;
 		}

 		if (ignore_cache) {
 			if (buffer_dirty(bh)) {
 				/* This should probably be a BUG, or
 				 * at least return an error. */
 				mlog(ML_BH_IO, "asking me to sync read a dirty "
 					       "buffer! (blocknr = %llu)\n",
 				     (unsigned long long)bh->b_blocknr);
 				continue;
 			}

 			/* A read-ahead request was made - if the
 			 * buffer is already under read-ahead from a
 			 * previously submitted request than we are
 			 * done here. */
 			if ((flags & OCFS2_BH_READAHEAD)
 			    && ocfs2_buffer_read_ahead(inode, bh))
 				continue;

 			lock_buffer(bh);
 			if (buffer_jbd(bh)) {
 #ifdef CATCH_BH_JBD_RACES
 				mlog(ML_ERROR, "block %llu had the JBD bit set "
 					       "while I was in lock_buffer!",
 				     (unsigned long long)bh->b_blocknr);
 				BUG();
 #else
 				unlock_buffer(bh);
 				continue;
 #endif
 			}

 			/* Re-check ocfs2_buffer_uptodate() as a
 			 * previously read-ahead buffer may have
 			 * completed I/O while we were waiting for the
 			 * buffer lock. */
 			if (!(flags & OCFS2_BH_IGNORE_CACHE)
 			    && !(flags & OCFS2_BH_READAHEAD)
 			    && ocfs2_buffer_uptodate(inode, bh)) {
 				unlock_buffer(bh);
 				continue;
 			}

 			clear_buffer_uptodate(bh);
 			get_bh(bh); /* for end_buffer_read_sync() */
 			bh->b_end_io = end_buffer_read_sync;
 			submit_bh(READ, bh);
 			continue;
 		}
 	}

 	status = 0;

 	for (i = (nr - 1); i >= 0; i--) {
 		bh = bhs[i];

 		if (!(flags & OCFS2_BH_READAHEAD)) {
 			/* We know this can't have changed as we hold the
 			 * inode sem. Avoid doing any work on the bh if the
 			 * journal has it. */
 			if (!buffer_jbd(bh))
 				wait_on_buffer(bh);

 			if (!buffer_uptodate(bh)) {
 				/* Status won't be cleared from here on out,
 				 * so we can safely record this and loop back
 				 * to cleanup the other buffers. Don't need to
 				 * remove the clustered uptodate information
 				 * for this bh as it's not marked locally
 				 * uptodate. */
 				status = -EIO;
 				put_bh(bh);
 				bhs[i] = NULL;
 				continue;
 			}
 		}

 		/* Always set the buffer in the cache, even if it was
 		 * a forced read, or read-ahead which hasn't yet
 		 * completed. */
 		ocfs2_set_buffer_uptodate(inode, bh);
 	}
 	mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);

 	mlog(ML_BH_IO, "block=(%llu), nr=(%d), cached=%s, flags=0x%x\n",
 	     (unsigned long long)block, nr,
 	     ((flags & OCFS2_BH_IGNORE_CACHE) || ignore_cache) ? "no" : "yes",
 	     flags);

 bail:

 	mlog_exit(status);
 	return status;
 }

 /* Check whether the blkno is the super block or one of the backups. */
 static void ocfs2_check_super_or_backup(struct super_block *sb,
 					sector_t blkno)
 {
 	int i;
 	u64 backup_blkno;

 	if (blkno == OCFS2_SUPER_BLOCK_BLKNO)
 		return;

 	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
 		backup_blkno = ocfs2_backup_super_blkno(sb, i);
 		if (backup_blkno == blkno)
 			return;
 	}

 	BUG();
 }

 /*
  * Write super block and backups doesn't need to collaborate with journal,
  * so we don't need to lock ip_io_mutex and inode doesn't need to bea passed
  * into this function.
  */
 int ocfs2_write_super_or_backup(struct ocfs2_super *osb,
 				struct buffer_head *bh)
 {
 	int ret = 0;

 	mlog_entry_void();

 	BUG_ON(buffer_jbd(bh));
 	ocfs2_check_super_or_backup(osb->sb, bh->b_blocknr);

 	if (ocfs2_is_hard_readonly(osb) || ocfs2_is_soft_readonly(osb)) {
 		ret = -EROFS;
 		goto out;
 	}

 	lock_buffer(bh);
 	set_buffer_uptodate(bh);

 	/* remove from dirty list before I/O. */
 	clear_buffer_dirty(bh);

 	get_bh(bh); /* for end_buffer_write_sync() */
 	bh->b_end_io = end_buffer_write_sync;
 	submit_bh(WRITE, bh);

 	wait_on_buffer(bh);

 	if (!buffer_uptodate(bh)) {
 		ret = -EIO;
 		put_bh(bh);
 	}

 out:
 	mlog_exit(ret);
 	return ret;
 }
	/* -- mode: c; c-basic-offset: 8; --
	* vim: noexpandtab sw=8 ts=8 sts=0:
	*
	* io.c
	*
	* Buffer cache handling
	*
	* Copyright (C) 2002, 2004 Oracle. All rights reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public
	* License as published by the Free Software Foundation; either
	* version 2 of the License, or (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public
	* License along with this program; if not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* Boston, MA 021110-1307, USA.
	*/

	#include <linux/fs.h>
	#include <linux/types.h>
	#include <linux/slab.h>
	#include <linux/highmem.h>

	#include <cluster/masklog.h>

	#include "ocfs2.h"

	#include "alloc.h"
	#include "inode.h"
	#include "journal.h"
	#include "uptodate.h"

	#include "buffer_head_io.h"

	int ocfs2_write_block(struct ocfs2_super osb, struct buffer_head bh,
	struct inode *inode)
	{
	int ret = 0;

	mlog_entry("(bh->b_blocknr = %llu, inode=%p)\n",
	(unsigned long long)bh->b_blocknr, inode);

	BUG_ON(bh->b_blocknr < OCFS2_SUPER_BLOCK_BLKNO);
	BUG_ON(buffer_jbd(bh));

	/* No need to check for a soft readonly file system here. non
	* journalled writes are only ever done on system files which
	* can get modified during recovery even if read-only. */
	if (ocfs2_is_hard_readonly(osb)) {
	ret = -EROFS;
	goto out;
	}

	mutex_lock(&OCFS2_I(inode)->ip_io_mutex);

	lock_buffer(bh);
	set_buffer_uptodate(bh);

	/* remove from dirty list before I/O. */
	clear_buffer_dirty(bh);

	get_bh(bh); /* for end_buffer_write_sync() */
	bh->b_end_io = end_buffer_write_sync;
	submit_bh(WRITE, bh);

	wait_on_buffer(bh);

	if (buffer_uptodate(bh)) {
	ocfs2_set_buffer_uptodate(inode, bh);
	} else {
	/* We don't need to remove the clustered uptodate
	* information for this bh as it's not marked locally
	* uptodate. */
	ret = -EIO;
	put_bh(bh);
	}

	mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);
	out:
	mlog_exit(ret);
	return ret;
	}

	int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
	unsigned int nr, struct buffer_head *bhs[])
	{
	int status = 0;
	unsigned int i;
	struct buffer_head *bh;

	if (!nr) {
	mlog(ML_BH_IO, "No buffers will be read!\n");
	goto bail;
	}

	for (i = 0 ; i < nr ; i++) {
	if (bhs[i] == NULL) {
	bhs[i] = sb_getblk(osb->sb, block++);
	if (bhs[i] == NULL) {
	status = -EIO;
	mlog_errno(status);
	goto bail;
	}
	}
	bh = bhs[i];

	if (buffer_jbd(bh)) {
	mlog(ML_ERROR,
	"trying to sync read a jbd "
	"managed bh (blocknr = %llu), skipping\n",
	(unsigned long long)bh->b_blocknr);
	continue;
	}

	if (buffer_dirty(bh)) {
	/* This should probably be a BUG, or
	* at least return an error. */
	mlog(ML_ERROR,
	"trying to sync read a dirty "
	"buffer! (blocknr = %llu), skipping\n",
	(unsigned long long)bh->b_blocknr);
	continue;
	}

	lock_buffer(bh);
	if (buffer_jbd(bh)) {
	mlog(ML_ERROR,
	"block %llu had the JBD bit set "
	"while I was in lock_buffer!",
	(unsigned long long)bh->b_blocknr);
	BUG();
	}

	clear_buffer_uptodate(bh);
	get_bh(bh); /* for end_buffer_read_sync() */
	bh->b_end_io = end_buffer_read_sync;
	submit_bh(READ, bh);
	}

	for (i = nr; i > 0; i--) {
	bh = bhs[i - 1];

	if (buffer_jbd(bh)) {
	mlog(ML_ERROR,
	"the journal got the buffer while it was "
	"locked for io! (blocknr = %llu)\n",
	(unsigned long long)bh->b_blocknr);
	BUG();
	}

	wait_on_buffer(bh);
	if (!buffer_uptodate(bh)) {
	/* Status won't be cleared from here on out,
	* so we can safely record this and loop back
	* to cleanup the other buffers. */
	status = -EIO;
	put_bh(bh);
	bhs[i - 1] = NULL;
	}
	}

	bail:
	return status;
	}

	int ocfs2_read_blocks(struct inode *inode, u64 block, int nr,
	struct buffer_head *bhs[], int flags)
	{
	int status = 0;
	int i, ignore_cache = 0;
	struct buffer_head *bh;

	mlog_entry("(inode=%p, block=(%llu), nr=(%d), flags=%d)\n",
	inode, (unsigned long long)block, nr, flags);

	BUG_ON(!inode);
	BUG_ON((flags & OCFS2_BH_READAHEAD) &&
	(flags & OCFS2_BH_IGNORE_CACHE));

	if (bhs == NULL) {
	status = -EINVAL;
	mlog_errno(status);
	goto bail;
	}

	if (nr < 0) {
	mlog(ML_ERROR, "asked to read %d blocks!\n", nr);
	status = -EINVAL;
	mlog_errno(status);
	goto bail;
	}

	if (nr == 0) {
	mlog(ML_BH_IO, "No buffers will be read!\n");
	status = 0;
	goto bail;
	}

	mutex_lock(&OCFS2_I(inode)->ip_io_mutex);
	for (i = 0 ; i < nr ; i++) {
	if (bhs[i] == NULL) {
	bhs[i] = sb_getblk(inode->i_sb, block++);
	if (bhs[i] == NULL) {
	mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);
	status = -EIO;
	mlog_errno(status);
	goto bail;
	}
	}
	bh = bhs[i];
	ignore_cache = (flags & OCFS2_BH_IGNORE_CACHE);

	/* There are three read-ahead cases here which we need to
	* be concerned with. All three assume a buffer has
	* previously been submitted with OCFS2_BH_READAHEAD
	* and it hasn't yet completed I/O.
	*
	* 1) The current request is sync to disk. This rarely
	* happens these days, and never when performance
	* matters - the code can just wait on the buffer
	* lock and re-submit.
	*
	* 2) The current request is cached, but not
	* readahead. ocfs2_buffer_uptodate() will return
	* false anyway, so we'll wind up waiting on the
	* buffer lock to do I/O. We re-check the request
	* with after getting the lock to avoid a re-submit.
	*
	* 3) The current request is readahead (and so must
	* also be a caching one). We short circuit if the
	* buffer is locked (under I/O) and if it's in the
	* uptodate cache. The re-check from #2 catches the
	* case that the previous read-ahead completes just
	* before our is-it-in-flight check.
	*/

	if (!ignore_cache && !ocfs2_buffer_uptodate(inode, bh)) {
	mlog(ML_UPTODATE,
	"bh (%llu), inode %llu not uptodate\n",
	(unsigned long long)bh->b_blocknr,
	(unsigned long long)OCFS2_I(inode)->ip_blkno);
	/* We're using ignore_cache here to say
	* "go to disk" */
	ignore_cache = 1;
	}

	/* XXX: Can we ever get this and not have the cached
	* flag set? */
	if (buffer_jbd(bh)) {
	if (ignore_cache)
	mlog(ML_BH_IO, "trying to sync read a jbd "
	"managed bh (blocknr = %llu)\n",
	(unsigned long long)bh->b_blocknr);
	continue;
	}

	if (ignore_cache) {
	if (buffer_dirty(bh)) {
	/* This should probably be a BUG, or
	* at least return an error. */
	mlog(ML_BH_IO, "asking me to sync read a dirty "
	"buffer! (blocknr = %llu)\n",
	(unsigned long long)bh->b_blocknr);
	continue;
	}

	/* A read-ahead request was made - if the
	* buffer is already under read-ahead from a
	* previously submitted request than we are
	* done here. */
	if ((flags & OCFS2_BH_READAHEAD)
	&& ocfs2_buffer_read_ahead(inode, bh))
	continue;

	lock_buffer(bh);
	if (buffer_jbd(bh)) {
	#ifdef CATCH_BH_JBD_RACES
	mlog(ML_ERROR, "block %llu had the JBD bit set "
	"while I was in lock_buffer!",
	(unsigned long long)bh->b_blocknr);
	BUG();
	#else
	unlock_buffer(bh);
	continue;
	#endif
	}

	/* Re-check ocfs2_buffer_uptodate() as a
	* previously read-ahead buffer may have
	* completed I/O while we were waiting for the
	* buffer lock. */
	if (!(flags & OCFS2_BH_IGNORE_CACHE)
	&& !(flags & OCFS2_BH_READAHEAD)
	&& ocfs2_buffer_uptodate(inode, bh)) {
	unlock_buffer(bh);
	continue;
	}

	clear_buffer_uptodate(bh);
	get_bh(bh); /* for end_buffer_read_sync() */
	bh->b_end_io = end_buffer_read_sync;
	submit_bh(READ, bh);
	continue;
	}
	}

	status = 0;

	for (i = (nr - 1); i >= 0; i--) {
	bh = bhs[i];

	if (!(flags & OCFS2_BH_READAHEAD)) {
	/* We know this can't have changed as we hold the
	* inode sem. Avoid doing any work on the bh if the
	* journal has it. */
	if (!buffer_jbd(bh))
	wait_on_buffer(bh);

	if (!buffer_uptodate(bh)) {
	/* Status won't be cleared from here on out,
	* so we can safely record this and loop back
	* to cleanup the other buffers. Don't need to
	* remove the clustered uptodate information
	* for this bh as it's not marked locally
	* uptodate. */
	status = -EIO;
	put_bh(bh);
	bhs[i] = NULL;
	continue;
	}
	}

	/* Always set the buffer in the cache, even if it was
	* a forced read, or read-ahead which hasn't yet
	* completed. */
	ocfs2_set_buffer_uptodate(inode, bh);
	}
	mutex_unlock(&OCFS2_I(inode)->ip_io_mutex);

	mlog(ML_BH_IO, "block=(%llu), nr=(%d), cached=%s, flags=0x%x\n",
	(unsigned long long)block, nr,
	((flags & OCFS2_BH_IGNORE_CACHE) \|\| ignore_cache) ? "no" : "yes",
	flags);

	bail:

	mlog_exit(status);
	return status;
	}

	/* Check whether the blkno is the super block or one of the backups. */
	static void ocfs2_check_super_or_backup(struct super_block *sb,
	sector_t blkno)
	{
	int i;
	u64 backup_blkno;

	if (blkno == OCFS2_SUPER_BLOCK_BLKNO)
	return;

	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
	backup_blkno = ocfs2_backup_super_blkno(sb, i);
	if (backup_blkno == blkno)
	return;
	}

	BUG();
	}

	/*
	* Write super block and backups doesn't need to collaborate with journal,
	* so we don't need to lock ip_io_mutex and inode doesn't need to bea passed
	* into this function.
	*/
	int ocfs2_write_super_or_backup(struct ocfs2_super *osb,
	struct buffer_head *bh)
	{
	int ret = 0;

	mlog_entry_void();

	BUG_ON(buffer_jbd(bh));
	ocfs2_check_super_or_backup(osb->sb, bh->b_blocknr);

	if (ocfs2_is_hard_readonly(osb) \|\| ocfs2_is_soft_readonly(osb)) {
	ret = -EROFS;
	goto out;
	}

	lock_buffer(bh);
	set_buffer_uptodate(bh);

	/* remove from dirty list before I/O. */
	clear_buffer_dirty(bh);

	get_bh(bh); /* for end_buffer_write_sync() */
	bh->b_end_io = end_buffer_write_sync;
	submit_bh(WRITE, bh);

	wait_on_buffer(bh);

	if (!buffer_uptodate(bh)) {
	ret = -EIO;
	put_bh(bh);
	}

	out:
	mlog_exit(ret);
	return ret;
	}