[deliverable/linux.git] / fs / gfs2 / meta_io.c

/*
 * 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_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;

	if (mapping == NULL)
		mapping = &sdp->sd_aspace;

	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;
	int was_pinned = 0;

	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)
			tr->tr_num_buf_rm++;
		else
			tr->tr_num_databuf_rm++;
		tr->tr_touched = 1;
		was_pinned = 1;
		brelse(bh);
	}
	if (bd) {
		spin_lock(&sdp->sd_ail_lock);
		if (bd->bd_tr) {
			gfs2_trans_add_revoke(sdp, bd);
		} else if (was_pinned) {
			bh->b_private = NULL;
			kmem_cache_free(gfs2_bufdata_cachep, 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;
}
Commit	Line	Data
	1	/*
	2	* Copyright (C) Sistina Software, Inc. 1997-2003 All rights reserved.
	3	* Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
	4	*
	5	* This copyrighted material is made available to anyone wishing to use,
	6	* modify, copy, or redistribute it subject to the terms and conditions
	7	* of the GNU General Public License version 2.
	8	*/
	9
	10	#include <linux/sched.h>
	11	#include <linux/slab.h>
	12	#include <linux/spinlock.h>
	13	#include <linux/completion.h>
	14	#include <linux/buffer_head.h>
	15	#include <linux/mm.h>
	16	#include <linux/pagemap.h>
	17	#include <linux/writeback.h>
	18	#include <linux/swap.h>
	19	#include <linux/delay.h>
	20	#include <linux/bio.h>
	21	#include <linux/gfs2_ondisk.h>
	22
	23	#include "gfs2.h"
	24	#include "incore.h"
	25	#include "glock.h"
	26	#include "glops.h"
	27	#include "inode.h"
	28	#include "log.h"
	29	#include "lops.h"
	30	#include "meta_io.h"
	31	#include "rgrp.h"
	32	#include "trans.h"
	33	#include "util.h"
	34	#include "trace_gfs2.h"
	35
	36	static int gfs2_aspace_writepage(struct page page, struct writeback_control wbc)
	37	{
	38	struct buffer_head bh, head;
	39	int nr_underway = 0;
	40	int write_op = REQ_META \| REQ_PRIO \|
	41	(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
	42
	43	BUG_ON(!PageLocked(page));
	44	BUG_ON(!page_has_buffers(page));
	45
	46	head = page_buffers(page);
	47	bh = head;
	48
	49	do {
	50	if (!buffer_mapped(bh))
	51	continue;
	52	/*
	53	* If it's a fully non-blocking write attempt and we cannot
	54	* lock the buffer then redirty the page. Note that this can
	55	* potentially cause a busy-wait loop from flusher thread and kswapd
	56	* activity, but those code paths have their own higher-level
	57	* throttling.
	58	*/
	59	if (wbc->sync_mode != WB_SYNC_NONE) {
	60	lock_buffer(bh);
	61	} else if (!trylock_buffer(bh)) {
	62	redirty_page_for_writepage(wbc, page);
	63	continue;
	64	}
	65	if (test_clear_buffer_dirty(bh)) {
	66	mark_buffer_async_write(bh);
	67	} else {
	68	unlock_buffer(bh);
	69	}
	70	} while ((bh = bh->b_this_page) != head);
	71
	72	/*
	73	* The page and its buffers are protected by PageWriteback(), so we can
	74	* drop the bh refcounts early.
	75	*/
	76	BUG_ON(PageWriteback(page));
	77	set_page_writeback(page);
	78
	79	do {
	80	struct buffer_head *next = bh->b_this_page;
	81	if (buffer_async_write(bh)) {
	82	submit_bh(write_op, bh);
	83	nr_underway++;
	84	}
	85	bh = next;
	86	} while (bh != head);
	87	unlock_page(page);
	88
	89	if (nr_underway == 0)
	90	end_page_writeback(page);
	91
	92	return 0;
	93	}
	94
	95	const struct address_space_operations gfs2_meta_aops = {
	96	.writepage = gfs2_aspace_writepage,
	97	.releasepage = gfs2_releasepage,
	98	};
	99
	100	/**
	101	* gfs2_getbuf - Get a buffer with a given address space
	102	* @gl: the glock
	103	* @blkno: the block number (filesystem scope)
	104	* @create: 1 if the buffer should be created
	105	*
	106	* Returns: the buffer
	107	*/
	108
	109	struct buffer_head gfs2_getbuf(struct gfs2_glock gl, u64 blkno, int create)
	110	{
	111	struct address_space *mapping = gfs2_glock2aspace(gl);
	112	struct gfs2_sbd *sdp = gl->gl_sbd;
	113	struct page *page;
	114	struct buffer_head *bh;
	115	unsigned int shift;
	116	unsigned long index;
	117	unsigned int bufnum;
	118
	119	if (mapping == NULL)
	120	mapping = &sdp->sd_aspace;
	121
	122	shift = PAGE_CACHE_SHIFT - sdp->sd_sb.sb_bsize_shift;
	123	index = blkno >> shift; /* convert block to page */
	124	bufnum = blkno - (index << shift); /* block buf index within page */
	125
	126	if (create) {
	127	for (;;) {
	128	page = grab_cache_page(mapping, index);
	129	if (page)
	130	break;
	131	yield();
	132	}
	133	} else {
	134	page = find_lock_page(mapping, index);
	135	if (!page)
	136	return NULL;
	137	}
	138
	139	if (!page_has_buffers(page))
	140	create_empty_buffers(page, sdp->sd_sb.sb_bsize, 0);
	141
	142	/* Locate header for our buffer within our page */
	143	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
	144	/* Do nothing */;
	145	get_bh(bh);
	146
	147	if (!buffer_mapped(bh))
	148	map_bh(bh, sdp->sd_vfs, blkno);
	149
	150	unlock_page(page);
	151	mark_page_accessed(page);
	152	page_cache_release(page);
	153
	154	return bh;
	155	}
	156
	157	static void meta_prep_new(struct buffer_head *bh)
	158	{
	159	struct gfs2_meta_header mh = (struct gfs2_meta_header )bh->b_data;
	160
	161	lock_buffer(bh);
	162	clear_buffer_dirty(bh);
	163	set_buffer_uptodate(bh);
	164	unlock_buffer(bh);
	165
	166	mh->mh_magic = cpu_to_be32(GFS2_MAGIC);
	167	}
	168
	169	/**
	170	* gfs2_meta_new - Get a block
	171	* @gl: The glock associated with this block
	172	* @blkno: The block number
	173	*
	174	* Returns: The buffer
	175	*/
	176
	177	struct buffer_head gfs2_meta_new(struct gfs2_glock gl, u64 blkno)
	178	{
	179	struct buffer_head *bh;
	180	bh = gfs2_getbuf(gl, blkno, CREATE);
	181	meta_prep_new(bh);
	182	return bh;
	183	}
	184
	185	/**
	186	* gfs2_meta_read - Read a block from disk
	187	* @gl: The glock covering the block
	188	* @blkno: The block number
	189	* @flags: flags
	190	* @bhp: the place where the buffer is returned (NULL on failure)
	191	*
	192	* Returns: errno
	193	*/
	194
	195	int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
	196	struct buffer_head **bhp)
	197	{
	198	struct gfs2_sbd *sdp = gl->gl_sbd;
	199	struct buffer_head *bh;
	200
	201	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
	202	*bhp = NULL;
	203	return -EIO;
	204	}
	205
	206	*bhp = bh = gfs2_getbuf(gl, blkno, CREATE);
	207
	208	lock_buffer(bh);
	209	if (buffer_uptodate(bh)) {
	210	unlock_buffer(bh);
	211	return 0;
	212	}
	213	bh->b_end_io = end_buffer_read_sync;
	214	get_bh(bh);
	215	submit_bh(READ_SYNC \| REQ_META \| REQ_PRIO, bh);
	216	if (!(flags & DIO_WAIT))
	217	return 0;
	218
	219	wait_on_buffer(bh);
	220	if (unlikely(!buffer_uptodate(bh))) {
	221	struct gfs2_trans *tr = current->journal_info;
	222	if (tr && tr->tr_touched)
	223	gfs2_io_error_bh(sdp, bh);
	224	brelse(bh);
	225	*bhp = NULL;
	226	return -EIO;
	227	}
	228
	229	return 0;
	230	}
	231
	232	/**
	233	* gfs2_meta_wait - Reread a block from disk
	234	* @sdp: the filesystem
	235	* @bh: The block to wait for
	236	*
	237	* Returns: errno
	238	*/
	239
	240	int gfs2_meta_wait(struct gfs2_sbd sdp, struct buffer_head bh)
	241	{
	242	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
	243	return -EIO;
	244
	245	wait_on_buffer(bh);
	246
	247	if (!buffer_uptodate(bh)) {
	248	struct gfs2_trans *tr = current->journal_info;
	249	if (tr && tr->tr_touched)
	250	gfs2_io_error_bh(sdp, bh);
	251	return -EIO;
	252	}
	253	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
	254	return -EIO;
	255
	256	return 0;
	257	}
	258
	259	void gfs2_remove_from_journal(struct buffer_head bh, struct gfs2_trans tr, int meta)
	260	{
	261	struct address_space *mapping = bh->b_page->mapping;
	262	struct gfs2_sbd *sdp = gfs2_mapping2sbd(mapping);
	263	struct gfs2_bufdata *bd = bh->b_private;
	264	int was_pinned = 0;
	265
	266	if (test_clear_buffer_pinned(bh)) {
	267	trace_gfs2_pin(bd, 0);
	268	atomic_dec(&sdp->sd_log_pinned);
	269	list_del_init(&bd->bd_list);
	270	if (meta)
	271	tr->tr_num_buf_rm++;
	272	else
	273	tr->tr_num_databuf_rm++;
	274	tr->tr_touched = 1;
	275	was_pinned = 1;
	276	brelse(bh);
	277	}
	278	if (bd) {
	279	spin_lock(&sdp->sd_ail_lock);
	280	if (bd->bd_tr) {
	281	gfs2_trans_add_revoke(sdp, bd);
	282	} else if (was_pinned) {
	283	bh->b_private = NULL;
	284	kmem_cache_free(gfs2_bufdata_cachep, bd);
	285	}
	286	spin_unlock(&sdp->sd_ail_lock);
	287	}
	288	clear_buffer_dirty(bh);
	289	clear_buffer_uptodate(bh);
	290	}
	291
	292	/**
	293	* gfs2_meta_wipe - make inode's buffers so they aren't dirty/pinned anymore
	294	* @ip: the inode who owns the buffers
	295	* @bstart: the first buffer in the run
	296	* @blen: the number of buffers in the run
	297	*
	298	*/
	299
	300	void gfs2_meta_wipe(struct gfs2_inode *ip, u64 bstart, u32 blen)
	301	{
	302	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
	303	struct buffer_head *bh;
	304
	305	while (blen) {
	306	bh = gfs2_getbuf(ip->i_gl, bstart, NO_CREATE);
	307	if (bh) {
	308	lock_buffer(bh);
	309	gfs2_log_lock(sdp);
	310	gfs2_remove_from_journal(bh, current->journal_info, 1);
	311	gfs2_log_unlock(sdp);
	312	unlock_buffer(bh);
	313	brelse(bh);
	314	}
	315
	316	bstart++;
	317	blen--;
	318	}
	319	}
	320
	321	/**
	322	* gfs2_meta_indirect_buffer - Get a metadata buffer
	323	* @ip: The GFS2 inode
	324	* @height: The level of this buf in the metadata (indir addr) tree (if any)
	325	* @num: The block number (device relative) of the buffer
	326	* @bhp: the buffer is returned here
	327	*
	328	* Returns: errno
	329	*/
	330
	331	int gfs2_meta_indirect_buffer(struct gfs2_inode *ip, int height, u64 num,
	332	struct buffer_head **bhp)
	333	{
	334	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
	335	struct gfs2_glock *gl = ip->i_gl;
	336	struct buffer_head *bh;
	337	int ret = 0;
	338	u32 mtype = height ? GFS2_METATYPE_IN : GFS2_METATYPE_DI;
	339
	340	ret = gfs2_meta_read(gl, num, DIO_WAIT, &bh);
	341	if (ret == 0 && gfs2_metatype_check(sdp, bh, mtype)) {
	342	brelse(bh);
	343	ret = -EIO;
	344	}
	345	*bhp = bh;
	346	return ret;
	347	}
	348
	349	/**
	350	* gfs2_meta_ra - start readahead on an extent of a file
	351	* @gl: the glock the blocks belong to
	352	* @dblock: the starting disk block
	353	* @extlen: the number of blocks in the extent
	354	*
	355	* returns: the first buffer in the extent
	356	*/
	357
	358	struct buffer_head gfs2_meta_ra(struct gfs2_glock gl, u64 dblock, u32 extlen)
	359	{
	360	struct gfs2_sbd *sdp = gl->gl_sbd;
	361	struct buffer_head first_bh, bh;
	362	u32 max_ra = gfs2_tune_get(sdp, gt_max_readahead) >>
	363	sdp->sd_sb.sb_bsize_shift;
	364
	365	BUG_ON(!extlen);
	366
	367	if (max_ra < 1)
	368	max_ra = 1;
	369	if (extlen > max_ra)
	370	extlen = max_ra;
	371
	372	first_bh = gfs2_getbuf(gl, dblock, CREATE);
	373
	374	if (buffer_uptodate(first_bh))
	375	goto out;
	376	if (!buffer_locked(first_bh))
	377	ll_rw_block(READ_SYNC \| REQ_META, 1, &first_bh);
	378
	379	dblock++;
	380	extlen--;
	381
	382	while (extlen) {
	383	bh = gfs2_getbuf(gl, dblock, CREATE);
	384
	385	if (!buffer_uptodate(bh) && !buffer_locked(bh))
	386	ll_rw_block(READA \| REQ_META, 1, &bh);
	387	brelse(bh);
	388	dblock++;
	389	extlen--;
	390	if (!buffer_locked(first_bh) && buffer_uptodate(first_bh))
	391	goto out;
	392	}
	393
	394	wait_on_buffer(first_bh);
	395	out:
	396	return first_bh;
	397	}
	398