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NetBSD/sys/kern/vfs_cluster.c

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/* $NetBSD: vfs_cluster.c,v 1.21 1998/11/08 18:18:31 mycroft Exp $ */
/*-
* Copyright (c) 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)vfs_cluster.c 8.10 (Berkeley) 3/28/95
*/
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/trace.h>
#include <sys/malloc.h>
#include <sys/systm.h>
#include <sys/resourcevar.h>
#include <vm/vm.h>
int doreallocblks = 0;
#ifdef DEBUG
#include <sys/sysctl.h>
struct ctldebug debug13 = { "doreallocblks", &doreallocblks };
#endif
/*
* Local declarations
*/
struct buf *cluster_rbuild __P((struct vnode *, u_quad_t, struct buf *,
daddr_t, daddr_t, long, int, long));
void cluster_wbuild __P((struct vnode *, struct buf *, long,
daddr_t, int, daddr_t));
struct cluster_save *cluster_collectbufs __P((struct vnode *, struct buf *));
#ifdef DIAGNOSTIC
/*
* Set to 1 if reads of block zero should cause readahead to be done.
* Set to 0 treats a read of block zero as a non-sequential read.
*
* Setting to one assumes that most reads of block zero of files are due to
* sequential passes over the files (e.g. cat, sum) where additional blocks
* will soon be needed. Setting to zero assumes that the majority are
* surgical strikes to get particular info (e.g. size, file) where readahead
* blocks will not be used and, in fact, push out other potentially useful
* blocks from the cache. The former seems intuitive, but some quick tests
* showed that the latter performed better from a system-wide point of view.
*/
int doclusterraz = 0;
#define ISSEQREAD(vp, blk) \
(((blk) != 0 || doclusterraz) && \
((blk) == (vp)->v_lastr + 1 || (blk) == (vp)->v_lastr))
#else
#define ISSEQREAD(vp, blk) \
((blk) != 0 && ((blk) == (vp)->v_lastr + 1 || (blk) == (vp)->v_lastr))
#endif
/*
* This replaces bread. If this is a bread at the beginning of a file and
* lastr is 0, we assume this is the first read and we'll read up to two
* blocks if they are sequential. After that, we'll do regular read ahead
* in clustered chunks.
*
* There are 4 or 5 cases depending on how you count:
* Desired block is in the cache:
* 1 Not sequential access (0 I/Os).
* 2 Access is sequential, do read-ahead (1 ASYNC).
* Desired block is not in cache:
* 3 Not sequential access (1 SYNC).
* 4 Sequential access, next block is contiguous (1 SYNC).
* 5 Sequential access, next block is not contiguous (1 SYNC, 1 ASYNC)
*
* There are potentially two buffers that require I/O.
* bp is the block requested.
* rbp is the read-ahead block.
* If either is NULL, then you don't have to do the I/O.
*/
int
cluster_read(vp, filesize, lblkno, size, cred, bpp)
struct vnode *vp;
u_quad_t filesize;
daddr_t lblkno;
long size;
struct ucred *cred;
struct buf **bpp;
{
struct buf *bp, *rbp;
daddr_t blkno, ioblkno;
long flags;
int error, num_ra, alreadyincore;
#ifdef DIAGNOSTIC
if (size == 0)
panic("cluster_read: size = 0");
#endif
error = 0;
flags = B_READ;
*bpp = bp = getblk(vp, lblkno, size, 0, 0);
if (bp->b_flags & (B_DONE | B_DELWRI)) {
/*
* Desired block is in cache; do any readahead ASYNC.
* Case 1, 2.
*/
trace(TR_BREADHIT, pack(vp, size), lblkno);
flags |= B_ASYNC;
ioblkno = lblkno + (vp->v_ralen ? vp->v_ralen : 1);
alreadyincore = incore(vp, ioblkno) != NULL;
bp = NULL;
} else {
/* Block wasn't in cache, case 3, 4, 5. */
trace(TR_BREADMISS, pack(vp, size), lblkno);
bp->b_flags |= B_READ;
ioblkno = lblkno;
alreadyincore = 0;
curproc->p_stats->p_ru.ru_inblock++; /* XXX */
}
/*
* XXX
* Replace 1 with a window size based on some permutation of
* maxcontig and rot_delay. This will let you figure out how
* many blocks you should read-ahead (case 2, 4, 5).
*
* If the access isn't sequential, reset the window to 1.
* Note that a read to the same block is considered sequential.
* This catches the case where the file is being read sequentially,
* but at smaller than the filesystem block size.
*/
rbp = NULL;
if (!ISSEQREAD(vp, lblkno)) {
vp->v_ralen = 0;
vp->v_maxra = lblkno;
} else if ((u_quad_t)(ioblkno + 1) * (u_quad_t)size <= filesize &&
!alreadyincore &&
!(error = VOP_BMAP(vp, ioblkno, NULL, &blkno, &num_ra)) &&
blkno != -1) {
/*
* Reading sequentially, and the next block is not in the
* cache. We are going to try reading ahead.
*/
if (num_ra) {
/*
* If our desired readahead block had been read
* in a previous readahead but is no longer in
* core, then we may be reading ahead too far
* or are not using our readahead very rapidly.
* In this case we scale back the window.
*/
if (!alreadyincore && ioblkno <= vp->v_maxra)
vp->v_ralen = max(vp->v_ralen >> 1, 1);
/*
* There are more sequential blocks than our current
* window allows, scale up. Ideally we want to get
* in sync with the filesystem maxcontig value.
*/
else if (num_ra > vp->v_ralen && lblkno != vp->v_lastr)
vp->v_ralen = vp->v_ralen ?
min(num_ra, vp->v_ralen << 1) : 1;
if (num_ra > vp->v_ralen)
num_ra = vp->v_ralen;
}
if (num_ra) /* case 2, 4 */
rbp = cluster_rbuild(vp, filesize,
bp, ioblkno, blkno, size, num_ra, flags);
else if (ioblkno == lblkno) {
bp->b_blkno = blkno;
/* Case 5: check how many blocks to read ahead */
++ioblkno;
if (((u_quad_t)(ioblkno + 1) * (u_quad_t)size >
filesize) ||
incore(vp, ioblkno) ||
(error = VOP_BMAP(vp, ioblkno, NULL,
&blkno, &num_ra)) ||
blkno == -1)
goto skip_readahead;
/*
* Adjust readahead as above.
* Don't check alreadyincore, we know it is 0 from
* the previous conditional.
*/
if (num_ra) {
if (ioblkno <= vp->v_maxra)
vp->v_ralen = max(vp->v_ralen >> 1, 1);
else if (num_ra > vp->v_ralen &&
lblkno != vp->v_lastr)
vp->v_ralen = vp->v_ralen ?
min(num_ra,vp->v_ralen<<1) : 1;
if (num_ra > vp->v_ralen)
num_ra = vp->v_ralen;
}
flags |= B_ASYNC;
if (num_ra)
rbp = cluster_rbuild(vp, filesize,
NULL, ioblkno, blkno, size, num_ra, flags);
else {
rbp = getblk(vp, ioblkno, size, 0, 0);
rbp->b_flags |= flags;
rbp->b_blkno = blkno;
}
} else {
/* case 2; read ahead single block */
rbp = getblk(vp, ioblkno, size, 0, 0);
rbp->b_flags |= flags;
rbp->b_blkno = blkno;
}
if (rbp == bp) /* case 4 */
rbp = NULL;
else if (rbp) { /* case 2, 5 */
trace(TR_BREADMISSRA,
pack(vp, (num_ra + 1) * size), ioblkno);
curproc->p_stats->p_ru.ru_inblock++; /* XXX */
}
}
/* XXX Kirk, do we need to make sure the bp has creds? */
skip_readahead:
if (bp) {
if (bp->b_flags & (B_DONE | B_DELWRI))
panic("cluster_read: DONE bp");
else
error = VOP_STRATEGY(bp);
}
if (rbp) {
if (error || rbp->b_flags & (B_DONE | B_DELWRI)) {
rbp->b_flags &= ~(B_ASYNC | B_READ);
brelse(rbp);
} else
(void) VOP_STRATEGY(rbp);
}
/*
* Recalculate our maximum readahead
*/
if (rbp == NULL)
rbp = bp;
if (rbp)
vp->v_maxra = rbp->b_lblkno + (rbp->b_bcount / size) - 1;
if (bp)
return(biowait(bp));
return(error);
}
/*
* If blocks are contiguous on disk, use this to provide clustered
* read ahead. We will read as many blocks as possible sequentially
* and then parcel them up into logical blocks in the buffer hash table.
*/
struct buf *
cluster_rbuild(vp, filesize, bp, lbn, blkno, size, run, flags)
struct vnode *vp;
u_quad_t filesize;
struct buf *bp;
daddr_t lbn;
daddr_t blkno;
long size;
int run;
long flags;
{
struct cluster_save *b_save = 0;
struct buf *tbp;
daddr_t bn;
int i, inc;
#ifdef DIAGNOSTIC
if (size != vp->v_mount->mnt_stat.f_iosize)
panic("cluster_rbuild: size %ld != filesize %ld\n",
size, vp->v_mount->mnt_stat.f_iosize);
#endif
if ((u_quad_t)size * (u_quad_t)(lbn + run + 1) > filesize)
--run;
if (run == 0) {
if (!bp) {
bp = getblk(vp, lbn, size, 0, 0);
bp->b_blkno = blkno;
bp->b_flags |= flags;
}
return (bp);
}
if (!bp)
bp = getblk(vp, lbn, size, 0, 0);
bp->b_blkno = blkno;
/*
* If initial component of the cluster is already
* in core, terminate the cluster early.
*/
if (bp->b_flags & (B_DONE | B_DELWRI))
return (bp);
bp->b_flags |= flags;
/*
* If block size is not a multiple of page size there
* is no way of doing the necessary page moving, so
* terminate early.
*/
if (size != roundup(size, CLBYTES))
return (bp);
inc = btodb(size);
for (bn = blkno + inc, i = 1; i <= run; ++i, bn += inc) {
/*
* If a component of the cluster is already in core,
* terminate the cluster early.
*/
if (incore(vp, lbn + i))
break;
tbp = getblk(vp, lbn + i, size, 0, 0);
if (tbp->b_flags & (B_DONE | B_DELWRI)) {
brelse(tbp);
break;
}
/*
* If there are excess pages in the cluster buffer and
* this buffer can take some of them, then shift some
* of the excess to here.
*/
if (bp->b_bufsize > (i * size)) {
int freespace = MAXBSIZE - tbp->b_bufsize;
if (freespace > 0) {
int nbytes = bp->b_bufsize - (i * size);
if (nbytes > freespace)
nbytes = freespace;
/* move pages and update sizes */
pagemove(bp->b_data + bp->b_bufsize - nbytes,
tbp->b_data + tbp->b_bufsize,
nbytes);
bp->b_bufsize -= nbytes;
tbp->b_bufsize += nbytes;
}
}
/*
* If there there is no space for forming a composite
* cluster buffer with this one, terminate.
*/
if (bp->b_bufsize + size > MAXBSIZE) {
brelse(tbp);
break;
}
/*
* Have good candidate for cluster; make sure cluster
* save area is allocated etc.
*/
if (b_save == 0) {
bp->b_iodone = cluster_callback;
bp->b_flags |= B_CALL;
b_save = malloc(sizeof(struct buf *) * run +
sizeof(struct cluster_save),
M_SEGMENT, M_WAITOK);
b_save->bs_bufsize = b_save->bs_bcount = size;
b_save->bs_nchildren = 0;
b_save->bs_children = (struct buf **)(b_save + 1);
b_save->bs_saveaddr = bp->b_saveaddr;
bp->b_saveaddr = (caddr_t) b_save;
}
/*
* Move pages to the cluster buffer and update
* its size appropriately.
*/
pagemove(tbp->b_data, bp->b_data + bp->b_bufsize, size);
bp->b_bcount += size;
bp->b_bufsize += size;
tbp->b_bufsize -= size;
tbp->b_blkno = bn;
tbp->b_flags |= flags | B_READ | B_ASYNC;
b_save->bs_children[b_save->bs_nchildren++] = tbp;
}
return(bp);
}
/*
* Cleanup after a clustered read or write.
* This is complicated by the fact that any of the buffers might have
* extra memory (if there were no empty buffer headers at allocbuf time)
* that we will need to shift around.
*/
void
cluster_callback(bp)
struct buf *bp;
{
struct cluster_save *b_save;
struct buf *tbp;
long bsize;
caddr_t cp;
int error = 0;
/*
* Must propogate errors to all the components.
*/
if (bp->b_flags & B_ERROR)
error = bp->b_error;
b_save = (struct cluster_save *)(bp->b_saveaddr);
bp->b_saveaddr = b_save->bs_saveaddr;
bsize = b_save->bs_bufsize;
cp = (char *)bp->b_data + bsize * b_save->bs_nchildren;
/*
* Move memory from the large cluster buffer into the component
* buffers in reverse order and mark IO as done on these.
*/
while (b_save->bs_nchildren--) {
tbp = b_save->bs_children[b_save->bs_nchildren];
pagemove(cp, tbp->b_data, bsize);
tbp->b_bufsize += bsize;
tbp->b_bcount = bsize;
if (error) {
tbp->b_flags |= B_ERROR;
tbp->b_error = error;
}
biodone(tbp);
bp->b_bufsize -= bsize;
cp -= bsize;
}
/*
* If there was excess memory in the cluster buffer,
* slide it up adjacent to the remaining valid data.
*/
if (bp->b_bufsize != bsize) {
if (bp->b_bufsize < bsize)
panic("cluster_callback: too little memory");
pagemove((char *)bp->b_data + bp->b_bcount,
(char *)bp->b_data + bsize,
bp->b_bufsize - bsize);
}
bp->b_bcount = bsize;
bp->b_iodone = NULL;
free(b_save, M_SEGMENT);
if (bp->b_flags & B_ASYNC)
brelse(bp);
else {
bp->b_flags &= ~B_WANTED;
wakeup((caddr_t)bp);
}
}
/*
* Do clustered write for FFS.
*
* Three cases:
* 1. Write is not sequential (write asynchronously)
* Write is sequential:
* 2. beginning of cluster - begin cluster
* 3. middle of a cluster - add to cluster
* 4. end of a cluster - asynchronously write cluster
*/
void
cluster_write(bp, filesize)
struct buf *bp;
u_quad_t filesize;
{
struct vnode *vp;
daddr_t lbn;
int maxclen, cursize;
vp = bp->b_vp;
lbn = bp->b_lblkno;
/* Initialize vnode to beginning of file. */
if (lbn == 0)
vp->v_lasta = vp->v_clen = vp->v_cstart = vp->v_lastw = 0;
if (vp->v_clen == 0 || lbn != vp->v_lastw + 1 ||
(bp->b_blkno != vp->v_lasta + btodb(bp->b_bcount))) {
maxclen = MAXBSIZE / vp->v_mount->mnt_stat.f_iosize - 1;
if (vp->v_clen != 0) {
/*
* Next block is not sequential.
*
* If we are not writing at end of file, the process
* seeked to another point in the file since its
* last write, or we have reached our maximum
* cluster size, then push the previous cluster.
* Otherwise try reallocating to make it sequential.
*/
cursize = vp->v_lastw - vp->v_cstart + 1;
if (!doreallocblks ||
(u_quad_t)(lbn + 1) * bp->b_bcount != filesize ||
lbn != vp->v_lastw + 1 || vp->v_clen <= cursize) {
cluster_wbuild(vp, NULL, bp->b_bcount,
vp->v_cstart, cursize, lbn);
} else {
struct buf **bpp, **endbp;
struct cluster_save *buflist;
buflist = cluster_collectbufs(vp, bp);
endbp = &buflist->bs_children
[buflist->bs_nchildren - 1];
if (VOP_REALLOCBLKS(vp, buflist)) {
/*
* Failed, push the previous cluster.
*/
for (bpp = buflist->bs_children;
bpp < endbp; bpp++)
brelse(*bpp);
free(buflist, M_SEGMENT);
cluster_wbuild(vp, NULL, bp->b_bcount,
vp->v_cstart, cursize, lbn);
} else {
/*
* Succeeded, keep building cluster.
*/
for (bpp = buflist->bs_children;
bpp <= endbp; bpp++)
bdwrite(*bpp);
free(buflist, M_SEGMENT);
vp->v_lastw = lbn;
vp->v_lasta = bp->b_blkno;
return;
}
}
}
/*
* Consider beginning a cluster.
* If at end of file, make cluster as large as possible,
* otherwise find size of existing cluster.
*/
if ((u_quad_t)(lbn + 1) * (u_quad_t)bp->b_bcount != filesize &&
(VOP_BMAP(vp, lbn, NULL, &bp->b_blkno, &maxclen) ||
bp->b_blkno == -1)) {
bawrite(bp);
vp->v_clen = 0;
vp->v_lasta = bp->b_blkno;
vp->v_cstart = lbn + 1;
vp->v_lastw = lbn;
return;
}
vp->v_clen = maxclen;
if (maxclen == 0) { /* I/O not contiguous */
vp->v_cstart = lbn + 1;
bawrite(bp);
} else { /* Wait for rest of cluster */
vp->v_cstart = lbn;
bdwrite(bp);
}
} else if (lbn == vp->v_cstart + vp->v_clen) {
/*
* At end of cluster, write it out.
*/
cluster_wbuild(vp, bp, bp->b_bcount, vp->v_cstart,
vp->v_clen + 1, lbn);
vp->v_clen = 0;
vp->v_cstart = lbn + 1;
} else
/*
* In the middle of a cluster, so just delay the
* I/O for now.
*/
bdwrite(bp);
vp->v_lastw = lbn;
vp->v_lasta = bp->b_blkno;
}
/*
* This is an awful lot like cluster_rbuild...wish they could be combined.
* The last lbn argument is the current block on which I/O is being
* performed. Check to see that it doesn't fall in the middle of
* the current block (if last_bp == NULL).
*/
void
cluster_wbuild(vp, last_bp, size, start_lbn, len, lbn)
struct vnode *vp;
struct buf *last_bp;
long size;
daddr_t start_lbn;
int len;
daddr_t lbn;
{
struct cluster_save *b_save;
struct buf *bp, *tbp;
caddr_t cp;
int i, s;
#ifdef DIAGNOSTIC
if (size != vp->v_mount->mnt_stat.f_iosize)
panic("cluster_wbuild: size %ld != filesize %ld\n",
size, vp->v_mount->mnt_stat.f_iosize);
#endif
redo:
while ((!incore(vp, start_lbn) || start_lbn == lbn) && len) {
++start_lbn;
--len;
}
/* Get more memory for current buffer */
if (len <= 1) {
if (last_bp) {
bawrite(last_bp);
} else if (len) {
bp = getblk(vp, start_lbn, size, 0, 0);
/*
* The buffer may have been in the process of being
* reclaimed, and is no longer valid. If so, we'll
* get a new buffer here, which won't have B_DELWRI
* set. Detect this and just drop the buffer on the
* floor rather than writing it out.
*/
if (!(bp->b_flags & B_DELWRI))
brelse(bp);
else
bawrite(bp);
}
return;
}
bp = getblk(vp, start_lbn, size, 0, 0);
if (!(bp->b_flags & B_DELWRI)) {
++start_lbn;
--len;
brelse(bp);
goto redo;
}
/*
* Extra memory in the buffer, punt on this buffer.
* XXX we could handle this in most cases, but we would have to
* push the extra memory down to after our max possible cluster
* size and then potentially pull it back up if the cluster was
* terminated prematurely--too much hassle.
*/
if (bp->b_bcount != bp->b_bufsize) {
++start_lbn;
--len;
bawrite(bp);
goto redo;
}
--len;
b_save = malloc(sizeof(struct buf *) * len + sizeof(struct cluster_save),
M_SEGMENT, M_WAITOK);
b_save->bs_bcount = bp->b_bcount;
b_save->bs_bufsize = bp->b_bufsize;
b_save->bs_nchildren = 0;
b_save->bs_children = (struct buf **)(b_save + 1);
b_save->bs_saveaddr = bp->b_saveaddr;
bp->b_saveaddr = (caddr_t) b_save;
bp->b_flags |= B_CALL;
bp->b_iodone = cluster_callback;
cp = (char *)bp->b_data + size;
for (++start_lbn, i = 0; i < len; ++i, ++start_lbn) {
/*
* Block is not in core or the non-sequential block
* ending our cluster was part of the cluster (in which
* case we don't want to write it twice).
*/
if (!incore(vp, start_lbn) ||
(last_bp == NULL && start_lbn == lbn))
break;
/*
* Get the desired block buffer (unless it is the final
* sequential block whose buffer was passed in explictly
* as last_bp).
*/
if (last_bp == NULL || start_lbn != lbn) {
tbp = getblk(vp, start_lbn, size, 0, 0);
if (!(tbp->b_flags & B_DELWRI)) {
brelse(tbp);
break;
}
} else
tbp = last_bp;
++b_save->bs_nchildren;
/* Move memory from children to parent */
if (tbp->b_blkno != (bp->b_blkno + btodb(bp->b_bufsize))) {
printf("Clustered Block: %d addr %x bufsize: %ld\n",
bp->b_lblkno, bp->b_blkno, bp->b_bufsize);
printf("Child Block: %d addr: %x\n", tbp->b_lblkno,
tbp->b_blkno);
panic("Clustered write to wrong blocks");
}
pagemove(tbp->b_data, cp, size);
bp->b_bcount += size;
bp->b_bufsize += size;
tbp->b_bufsize -= size;
tbp->b_flags &= ~(B_READ | B_DONE | B_ERROR | B_DELWRI);
/*
* We might as well AGE the buffer here; it's either empty, or
* contains data that we couldn't get rid of (but wanted to).
*/
tbp->b_flags |= (B_ASYNC | B_AGE);
s = splbio();
reassignbuf(tbp, tbp->b_vp); /* put on clean list */
++tbp->b_vp->v_numoutput;
splx(s);
b_save->bs_children[i] = tbp;
cp += size;
}
if (i == 0) {
/* None to cluster */
bp->b_saveaddr = b_save->bs_saveaddr;
bp->b_flags &= ~B_CALL;
bp->b_iodone = NULL;
free(b_save, M_SEGMENT);
}
bawrite(bp);
if (i < len) {
len -= i + 1;
start_lbn += 1;
goto redo;
}
}
/*
* Collect together all the buffers in a cluster.
* Plus add one additional buffer.
*/
struct cluster_save *
cluster_collectbufs(vp, last_bp)
struct vnode *vp;
struct buf *last_bp;
{
struct cluster_save *buflist;
daddr_t lbn;
int i, len;
len = vp->v_lastw - vp->v_cstart + 1;
buflist = malloc(sizeof(struct buf *) * (len + 1) + sizeof(*buflist),
M_SEGMENT, M_WAITOK);
buflist->bs_nchildren = 0;
buflist->bs_children = (struct buf **)(buflist + 1);
for (lbn = vp->v_cstart, i = 0; i < len; lbn++, i++)
(void)bread(vp, lbn, last_bp->b_bcount, NOCRED,
&buflist->bs_children[i]);
buflist->bs_children[i] = last_bp;
buflist->bs_nchildren = i + 1;
return (buflist);
}
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