fs/gfs2/meta_io.c - maze/linux - Git at Google

 /*
  * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
  * Copyright (C) 2004-2008 Red Hat, Inc.  All rights reserved.
  *
  * This copyrighted material is made available to anyone wishing to use,
  * modify, copy, or redistribute it subject to the terms and conditions
  * of the GNU General Public License version 2.
  */

 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/completion.h>
 #include <linux/buffer_head.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/writeback.h>
 #include <linux/swap.h>
 #include <linux/delay.h>
 #include <linux/bio.h>
 #include <linux/gfs2_ondisk.h>

 #include "gfs2.h"
 #include "incore.h"
 #include "glock.h"
 #include "glops.h"
 #include "inode.h"
 #include "log.h"
 #include "lops.h"
 #include "meta_io.h"
 #include "rgrp.h"
 #include "trans.h"
 #include "util.h"
 #include "trace_gfs2.h"

 static int gfs2_aspace_writepage(struct page *page, struct writeback_control *wbc)
 {
 	struct buffer_head *bh, *head;
 	int nr_underway = 0;
 	int write_op = REQ_META | REQ_PRIO |
 		(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);

 	BUG_ON(!PageLocked(page));
 	BUG_ON(!page_has_buffers(page));

 	head = page_buffers(page);
 	bh = head;

 	do {
 		if (!buffer_mapped(bh))
 			continue;
 		/*
 		 * If it's a fully non-blocking write attempt and we cannot
 		 * lock the buffer then redirty the page.  Note that this can
 		 * potentially cause a busy-wait loop from flusher thread and kswapd
 		 * activity, but those code paths have their own higher-level
 		 * throttling.
 		 */
 		if (wbc->sync_mode != WB_SYNC_NONE) {
 			lock_buffer(bh);
 		} else if (!trylock_buffer(bh)) {
 			redirty_page_for_writepage(wbc, page);
 			continue;
 		}
 		if (test_clear_buffer_dirty(bh)) {
 			mark_buffer_async_write(bh);
 		} else {
 			unlock_buffer(bh);
 		}
 	} while ((bh = bh->b_this_page) != head);

 	/*
 	 * The page and its buffers are protected by PageWriteback(), so we can
 	 * drop the bh refcounts early.
 	 */
 	BUG_ON(PageWriteback(page));
 	set_page_writeback(page);

 	do {
 		struct buffer_head *next = bh->b_this_page;
 		if (buffer_async_write(bh)) {
 			submit_bh(write_op, bh);
 			nr_underway++;
 		}
 		bh = next;
 	} while (bh != head);
 	unlock_page(page);

 	if (nr_underway == 0)
 		end_page_writeback(page);

 	return 0;
 }

 const struct address_space_operations gfs2_meta_aops = {
 	.writepage = gfs2_aspace_writepage,
 	.releasepage = gfs2_releasepage,
 };

 /**
  * gfs2_meta_sync - Sync all buffers associated with a glock
  * @gl: The glock
  *
  */

 void gfs2_meta_sync(struct gfs2_glock *gl)
 {
 	struct address_space *mapping = gfs2_glock2aspace(gl);
 	int error;

 	filemap_fdatawrite(mapping);
 	error = filemap_fdatawait(mapping);

 	if (error)
 		gfs2_io_error(gl->gl_sbd);
 }

 /**
  * gfs2_getbuf - Get a buffer with a given address space
  * @gl: the glock
  * @blkno: the block number (filesystem scope)
  * @create: 1 if the buffer should be created
  *
  * Returns: the buffer
  */

 struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
 {
 	struct address_space *mapping = gfs2_glock2aspace(gl);
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct page *page;
 	struct buffer_head *bh;
 	unsigned int shift;
 	unsigned long index;
 	unsigned int bufnum;

 	shift = PAGE_CACHE_SHIFT - sdp->sd_sb.sb_bsize_shift;
 	index = blkno >> shift;             /* convert block to page */
 	bufnum = blkno - (index << shift);  /* block buf index within page */

 	if (create) {
 		for (;;) {
 			page = grab_cache_page(mapping, index);
 			if (page)
 				break;
 			yield();
 		}
 	} else {
 		page = find_lock_page(mapping, index);
 		if (!page)
 			return NULL;
 	}

 	if (!page_has_buffers(page))
 		create_empty_buffers(page, sdp->sd_sb.sb_bsize, 0);

 	/* Locate header for our buffer within our page */
 	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
 		/* Do nothing */;
 	get_bh(bh);

 	if (!buffer_mapped(bh))
 		map_bh(bh, sdp->sd_vfs, blkno);

 	unlock_page(page);
 	mark_page_accessed(page);
 	page_cache_release(page);

 	return bh;
 }

 static void meta_prep_new(struct buffer_head *bh)
 {
 	struct gfs2_meta_header *mh = (struct gfs2_meta_header *)bh->b_data;

 	lock_buffer(bh);
 	clear_buffer_dirty(bh);
 	set_buffer_uptodate(bh);
 	unlock_buffer(bh);

 	mh->mh_magic = cpu_to_be32(GFS2_MAGIC);
 }

 /**
  * gfs2_meta_new - Get a block
  * @gl: The glock associated with this block
  * @blkno: The block number
  *
  * Returns: The buffer
  */

 struct buffer_head *gfs2_meta_new(struct gfs2_glock *gl, u64 blkno)
 {
 	struct buffer_head *bh;
 	bh = gfs2_getbuf(gl, blkno, CREATE);
 	meta_prep_new(bh);
 	return bh;
 }

 /**
  * gfs2_meta_read - Read a block from disk
  * @gl: The glock covering the block
  * @blkno: The block number
  * @flags: flags
  * @bhp: the place where the buffer is returned (NULL on failure)
  *
  * Returns: errno
  */

 int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
 		   struct buffer_head **bhp)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct buffer_head *bh;

 	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
 		*bhp = NULL;
 		return -EIO;
 	}

 	*bhp = bh = gfs2_getbuf(gl, blkno, CREATE);

 	lock_buffer(bh);
 	if (buffer_uptodate(bh)) {
 		unlock_buffer(bh);
 		return 0;
 	}
 	bh->b_end_io = end_buffer_read_sync;
 	get_bh(bh);
 	submit_bh(READ_SYNC | REQ_META | REQ_PRIO, bh);
 	if (!(flags & DIO_WAIT))
 		return 0;

 	wait_on_buffer(bh);
 	if (unlikely(!buffer_uptodate(bh))) {
 		struct gfs2_trans *tr = current->journal_info;
 		if (tr && tr->tr_touched)
 			gfs2_io_error_bh(sdp, bh);
 		brelse(bh);
 		*bhp = NULL;
 		return -EIO;
 	}

 	return 0;
 }

 /**
  * gfs2_meta_wait - Reread a block from disk
  * @sdp: the filesystem
  * @bh: The block to wait for
  *
  * Returns: errno
  */

 int gfs2_meta_wait(struct gfs2_sbd *sdp, struct buffer_head *bh)
 {
 	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
 		return -EIO;

 	wait_on_buffer(bh);

 	if (!buffer_uptodate(bh)) {
 		struct gfs2_trans *tr = current->journal_info;
 		if (tr && tr->tr_touched)
 			gfs2_io_error_bh(sdp, bh);
 		return -EIO;
 	}
 	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
 		return -EIO;

 	return 0;
 }

 void gfs2_remove_from_journal(struct buffer_head *bh, struct gfs2_trans *tr, int meta)
 {
 	struct address_space *mapping = bh->b_page->mapping;
 	struct gfs2_sbd *sdp = gfs2_mapping2sbd(mapping);
 	struct gfs2_bufdata *bd = bh->b_private;

 	if (test_clear_buffer_pinned(bh)) {
 		trace_gfs2_pin(bd, 0);
 		atomic_dec(&sdp->sd_log_pinned);
 		list_del_init(&bd->bd_list);
 		if (meta) {
 			gfs2_assert_warn(sdp, sdp->sd_log_num_buf);
 			sdp->sd_log_num_buf--;
 			tr->tr_num_buf_rm++;
 		} else {
 			gfs2_assert_warn(sdp, sdp->sd_log_num_databuf);
 			sdp->sd_log_num_databuf--;
 			tr->tr_num_databuf_rm++;
 		}
 		tr->tr_touched = 1;
 		brelse(bh);
 	}
 	if (bd) {
 		spin_lock(&sdp->sd_ail_lock);
 		if (bd->bd_tr) {
 			gfs2_remove_from_ail(bd);
 			bh->b_private = NULL;
 			bd->bd_bh = NULL;
 			bd->bd_blkno = bh->b_blocknr;
 			gfs2_trans_add_revoke(sdp, bd);
 		}
 		spin_unlock(&sdp->sd_ail_lock);
 	}
 	clear_buffer_dirty(bh);
 	clear_buffer_uptodate(bh);
 }

 /**
  * gfs2_meta_wipe - make inode's buffers so they aren't dirty/pinned anymore
  * @ip: the inode who owns the buffers
  * @bstart: the first buffer in the run
  * @blen: the number of buffers in the run
  *
  */

 void gfs2_meta_wipe(struct gfs2_inode *ip, u64 bstart, u32 blen)
 {
 	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
 	struct buffer_head *bh;

 	while (blen) {
 		bh = gfs2_getbuf(ip->i_gl, bstart, NO_CREATE);
 		if (bh) {
 			lock_buffer(bh);
 			gfs2_log_lock(sdp);
 			gfs2_remove_from_journal(bh, current->journal_info, 1);
 			gfs2_log_unlock(sdp);
 			unlock_buffer(bh);
 			brelse(bh);
 		}

 		bstart++;
 		blen--;
 	}
 }

 /**
  * gfs2_meta_indirect_buffer - Get a metadata buffer
  * @ip: The GFS2 inode
  * @height: The level of this buf in the metadata (indir addr) tree (if any)
  * @num: The block number (device relative) of the buffer
  * @bhp: the buffer is returned here
  *
  * Returns: errno
  */

 int gfs2_meta_indirect_buffer(struct gfs2_inode *ip, int height, u64 num,
 			      struct buffer_head **bhp)
 {
 	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
 	struct gfs2_glock *gl = ip->i_gl;
 	struct buffer_head *bh;
 	int ret = 0;
 	u32 mtype = height ? GFS2_METATYPE_IN : GFS2_METATYPE_DI;

 	ret = gfs2_meta_read(gl, num, DIO_WAIT, &bh);
 	if (ret == 0 && gfs2_metatype_check(sdp, bh, mtype)) {
 		brelse(bh);
 		ret = -EIO;
 	}
 	*bhp = bh;
 	return ret;
 }

 /**
  * gfs2_meta_ra - start readahead on an extent of a file
  * @gl: the glock the blocks belong to
  * @dblock: the starting disk block
  * @extlen: the number of blocks in the extent
  *
  * returns: the first buffer in the extent
  */

 struct buffer_head *gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct buffer_head *first_bh, *bh;
 	u32 max_ra = gfs2_tune_get(sdp, gt_max_readahead) >>
 			  sdp->sd_sb.sb_bsize_shift;

 	BUG_ON(!extlen);

 	if (max_ra < 1)
 		max_ra = 1;
 	if (extlen > max_ra)
 		extlen = max_ra;

 	first_bh = gfs2_getbuf(gl, dblock, CREATE);

 	if (buffer_uptodate(first_bh))
 		goto out;
 	if (!buffer_locked(first_bh))
 		ll_rw_block(READ_SYNC | REQ_META, 1, &first_bh);

 	dblock++;
 	extlen--;

 	while (extlen) {
 		bh = gfs2_getbuf(gl, dblock, CREATE);

 		if (!buffer_uptodate(bh) && !buffer_locked(bh))
 			ll_rw_block(READA | REQ_META, 1, &bh);
 		brelse(bh);
 		dblock++;
 		extlen--;
 		if (!buffer_locked(first_bh) && buffer_uptodate(first_bh))
 			goto out;
 	}

 	wait_on_buffer(first_bh);
 out:
 	return first_bh;
 }
	/*
	* Copyright (C) Sistina Software, Inc. 1997-2003 All rights reserved.
	* Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
	*
	* This copyrighted material is made available to anyone wishing to use,
	* modify, copy, or redistribute it subject to the terms and conditions
	* of the GNU General Public License version 2.
	*/

	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/completion.h>
	#include <linux/buffer_head.h>
	#include <linux/mm.h>
	#include <linux/pagemap.h>
	#include <linux/writeback.h>
	#include <linux/swap.h>
	#include <linux/delay.h>
	#include <linux/bio.h>
	#include <linux/gfs2_ondisk.h>

	#include "gfs2.h"
	#include "incore.h"
	#include "glock.h"
	#include "glops.h"
	#include "inode.h"
	#include "log.h"
	#include "lops.h"
	#include "meta_io.h"
	#include "rgrp.h"
	#include "trans.h"
	#include "util.h"
	#include "trace_gfs2.h"

	static int gfs2_aspace_writepage(struct page page, struct writeback_control wbc)
	{
	struct buffer_head bh, head;
	int nr_underway = 0;
	int write_op = REQ_META \| REQ_PRIO \|
	(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);

	BUG_ON(!PageLocked(page));
	BUG_ON(!page_has_buffers(page));

	head = page_buffers(page);
	bh = head;

	do {
	if (!buffer_mapped(bh))
	continue;
	/*
	* If it's a fully non-blocking write attempt and we cannot
	* lock the buffer then redirty the page. Note that this can
	* potentially cause a busy-wait loop from flusher thread and kswapd
	* activity, but those code paths have their own higher-level
	* throttling.
	*/
	if (wbc->sync_mode != WB_SYNC_NONE) {
	lock_buffer(bh);
	} else if (!trylock_buffer(bh)) {
	redirty_page_for_writepage(wbc, page);
	continue;
	}
	if (test_clear_buffer_dirty(bh)) {
	mark_buffer_async_write(bh);
	} else {
	unlock_buffer(bh);
	}
	} while ((bh = bh->b_this_page) != head);

	/*
	* The page and its buffers are protected by PageWriteback(), so we can
	* drop the bh refcounts early.
	*/
	BUG_ON(PageWriteback(page));
	set_page_writeback(page);

	do {
	struct buffer_head *next = bh->b_this_page;
	if (buffer_async_write(bh)) {
	submit_bh(write_op, bh);
	nr_underway++;
	}
	bh = next;
	} while (bh != head);
	unlock_page(page);

	if (nr_underway == 0)
	end_page_writeback(page);

	return 0;
	}

	const struct address_space_operations gfs2_meta_aops = {
	.writepage = gfs2_aspace_writepage,
	.releasepage = gfs2_releasepage,
	};

	/**
	* gfs2_meta_sync - Sync all buffers associated with a glock
	* @gl: The glock
	*
	*/

	void gfs2_meta_sync(struct gfs2_glock *gl)
	{
	struct address_space *mapping = gfs2_glock2aspace(gl);
	int error;

	filemap_fdatawrite(mapping);
	error = filemap_fdatawait(mapping);

	if (error)
	gfs2_io_error(gl->gl_sbd);
	}

	/**
	* gfs2_getbuf - Get a buffer with a given address space
	* @gl: the glock
	* @blkno: the block number (filesystem scope)
	* @create: 1 if the buffer should be created
	*
	* Returns: the buffer
	*/

	struct buffer_head gfs2_getbuf(struct gfs2_glock gl, u64 blkno, int create)
	{
	struct address_space *mapping = gfs2_glock2aspace(gl);
	struct gfs2_sbd *sdp = gl->gl_sbd;
	struct page *page;
	struct buffer_head *bh;
	unsigned int shift;
	unsigned long index;
	unsigned int bufnum;

	shift = PAGE_CACHE_SHIFT - sdp->sd_sb.sb_bsize_shift;
	index = blkno >> shift; /* convert block to page */
	bufnum = blkno - (index << shift); /* block buf index within page */

	if (create) {
	for (;;) {
	page = grab_cache_page(mapping, index);
	if (page)
	break;
	yield();
	}
	} else {
	page = find_lock_page(mapping, index);
	if (!page)
	return NULL;
	}

	if (!page_has_buffers(page))
	create_empty_buffers(page, sdp->sd_sb.sb_bsize, 0);

	/* Locate header for our buffer within our page */
	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
	/* Do nothing */;
	get_bh(bh);

	if (!buffer_mapped(bh))
	map_bh(bh, sdp->sd_vfs, blkno);

	unlock_page(page);
	mark_page_accessed(page);
	page_cache_release(page);

	return bh;
	}

	static void meta_prep_new(struct buffer_head *bh)
	{
	struct gfs2_meta_header mh = (struct gfs2_meta_header )bh->b_data;

	lock_buffer(bh);
	clear_buffer_dirty(bh);
	set_buffer_uptodate(bh);
	unlock_buffer(bh);

	mh->mh_magic = cpu_to_be32(GFS2_MAGIC);
	}

	/**
	* gfs2_meta_new - Get a block
	* @gl: The glock associated with this block
	* @blkno: The block number
	*
	* Returns: The buffer
	*/

	struct buffer_head gfs2_meta_new(struct gfs2_glock gl, u64 blkno)
	{
	struct buffer_head *bh;
	bh = gfs2_getbuf(gl, blkno, CREATE);
	meta_prep_new(bh);
	return bh;
	}

	/**
	* gfs2_meta_read - Read a block from disk
	* @gl: The glock covering the block
	* @blkno: The block number
	* @flags: flags
	* @bhp: the place where the buffer is returned (NULL on failure)
	*
	* Returns: errno
	*/

	int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
	struct buffer_head **bhp)
	{
	struct gfs2_sbd *sdp = gl->gl_sbd;
	struct buffer_head *bh;

	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
	*bhp = NULL;
	return -EIO;
	}

	*bhp = bh = gfs2_getbuf(gl, blkno, CREATE);

	lock_buffer(bh);
	if (buffer_uptodate(bh)) {
	unlock_buffer(bh);
	return 0;
	}
	bh->b_end_io = end_buffer_read_sync;
	get_bh(bh);
	submit_bh(READ_SYNC \| REQ_META \| REQ_PRIO, bh);
	if (!(flags & DIO_WAIT))
	return 0;

	wait_on_buffer(bh);
	if (unlikely(!buffer_uptodate(bh))) {
	struct gfs2_trans *tr = current->journal_info;
	if (tr && tr->tr_touched)
	gfs2_io_error_bh(sdp, bh);
	brelse(bh);
	*bhp = NULL;
	return -EIO;
	}

	return 0;
	}

	/**
	* gfs2_meta_wait - Reread a block from disk
	* @sdp: the filesystem
	* @bh: The block to wait for
	*
	* Returns: errno
	*/

	int gfs2_meta_wait(struct gfs2_sbd sdp, struct buffer_head bh)
	{
	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
	return -EIO;

	wait_on_buffer(bh);

	if (!buffer_uptodate(bh)) {
	struct gfs2_trans *tr = current->journal_info;
	if (tr && tr->tr_touched)
	gfs2_io_error_bh(sdp, bh);
	return -EIO;
	}
	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
	return -EIO;

	return 0;
	}

	void gfs2_remove_from_journal(struct buffer_head bh, struct gfs2_trans tr, int meta)
	{
	struct address_space *mapping = bh->b_page->mapping;
	struct gfs2_sbd *sdp = gfs2_mapping2sbd(mapping);
	struct gfs2_bufdata *bd = bh->b_private;

	if (test_clear_buffer_pinned(bh)) {
	trace_gfs2_pin(bd, 0);
	atomic_dec(&sdp->sd_log_pinned);
	list_del_init(&bd->bd_list);
	if (meta) {
	gfs2_assert_warn(sdp, sdp->sd_log_num_buf);
	sdp->sd_log_num_buf--;
	tr->tr_num_buf_rm++;
	} else {
	gfs2_assert_warn(sdp, sdp->sd_log_num_databuf);
	sdp->sd_log_num_databuf--;
	tr->tr_num_databuf_rm++;
	}
	tr->tr_touched = 1;
	brelse(bh);
	}
	if (bd) {
	spin_lock(&sdp->sd_ail_lock);
	if (bd->bd_tr) {
	gfs2_remove_from_ail(bd);
	bh->b_private = NULL;
	bd->bd_bh = NULL;
	bd->bd_blkno = bh->b_blocknr;
	gfs2_trans_add_revoke(sdp, bd);
	}
	spin_unlock(&sdp->sd_ail_lock);
	}
	clear_buffer_dirty(bh);
	clear_buffer_uptodate(bh);
	}

	/**
	* gfs2_meta_wipe - make inode's buffers so they aren't dirty/pinned anymore
	* @ip: the inode who owns the buffers
	* @bstart: the first buffer in the run
	* @blen: the number of buffers in the run
	*
	*/

	void gfs2_meta_wipe(struct gfs2_inode *ip, u64 bstart, u32 blen)
	{
	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
	struct buffer_head *bh;

	while (blen) {
	bh = gfs2_getbuf(ip->i_gl, bstart, NO_CREATE);
	if (bh) {
	lock_buffer(bh);
	gfs2_log_lock(sdp);
	gfs2_remove_from_journal(bh, current->journal_info, 1);
	gfs2_log_unlock(sdp);
	unlock_buffer(bh);
	brelse(bh);
	}

	bstart++;
	blen--;
	}
	}

	/**
	* gfs2_meta_indirect_buffer - Get a metadata buffer
	* @ip: The GFS2 inode
	* @height: The level of this buf in the metadata (indir addr) tree (if any)
	* @num: The block number (device relative) of the buffer
	* @bhp: the buffer is returned here
	*
	* Returns: errno
	*/

	int gfs2_meta_indirect_buffer(struct gfs2_inode *ip, int height, u64 num,
	struct buffer_head **bhp)
	{
	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
	struct gfs2_glock *gl = ip->i_gl;
	struct buffer_head *bh;
	int ret = 0;
	u32 mtype = height ? GFS2_METATYPE_IN : GFS2_METATYPE_DI;

	ret = gfs2_meta_read(gl, num, DIO_WAIT, &bh);
	if (ret == 0 && gfs2_metatype_check(sdp, bh, mtype)) {
	brelse(bh);
	ret = -EIO;
	}
	*bhp = bh;
	return ret;
	}

	/**
	* gfs2_meta_ra - start readahead on an extent of a file
	* @gl: the glock the blocks belong to
	* @dblock: the starting disk block
	* @extlen: the number of blocks in the extent
	*
	* returns: the first buffer in the extent
	*/

	struct buffer_head gfs2_meta_ra(struct gfs2_glock gl, u64 dblock, u32 extlen)
	{
	struct gfs2_sbd *sdp = gl->gl_sbd;
	struct buffer_head first_bh, bh;
	u32 max_ra = gfs2_tune_get(sdp, gt_max_readahead) >>
	sdp->sd_sb.sb_bsize_shift;

	BUG_ON(!extlen);

	if (max_ra < 1)
	max_ra = 1;
	if (extlen > max_ra)
	extlen = max_ra;

	first_bh = gfs2_getbuf(gl, dblock, CREATE);

	if (buffer_uptodate(first_bh))
	goto out;
	if (!buffer_locked(first_bh))
	ll_rw_block(READ_SYNC \| REQ_META, 1, &first_bh);

	dblock++;
	extlen--;

	while (extlen) {
	bh = gfs2_getbuf(gl, dblock, CREATE);

	if (!buffer_uptodate(bh) && !buffer_locked(bh))
	ll_rw_block(READA \| REQ_META, 1, &bh);
	brelse(bh);
	dblock++;
	extlen--;
	if (!buffer_locked(first_bh) && buffer_uptodate(first_bh))
	goto out;
	}

	wait_on_buffer(first_bh);
	out:
	return first_bh;
	}