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| Current File : //usr/src/usr.sbin/makefs/ffs/ffs_alloc.c |
/* $NetBSD: ffs_alloc.c,v 1.14 2004/06/20 22:20:18 jmc Exp $ */
/* From: NetBSD: ffs_alloc.c,v 1.50 2001/09/06 02:16:01 lukem Exp */
/*
* Copyright (c) 2002 Networks Associates Technology, Inc.
* All rights reserved.
*
* This software was developed for the FreeBSD Project by Marshall
* Kirk McKusick and Network Associates Laboratories, the Security
* Research Division of Network Associates, Inc. under DARPA/SPAWAR
* contract N66001-01-C-8035 ("CBOSS"), as part of the DARPA CHATS
* research program
*
* Copyright (c) 1982, 1986, 1989, 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. 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.
*
* @(#)ffs_alloc.c 8.19 (Berkeley) 7/13/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: release/9.1.0/usr.sbin/makefs/ffs/ffs_alloc.c 214921 2010-11-07 16:05:04Z cognet $");
#include <sys/param.h>
#include <sys/time.h>
#include <errno.h>
#include "makefs.h"
#include <ufs/ufs/dinode.h>
#include <ufs/ffs/fs.h>
#include "ffs/ufs_bswap.h"
#include "ffs/buf.h"
#include "ffs/ufs_inode.h"
#include "ffs/ffs_extern.h"
static int scanc(u_int, const u_char *, const u_char *, int);
static daddr_t ffs_alloccg(struct inode *, int, daddr_t, int);
static daddr_t ffs_alloccgblk(struct inode *, struct buf *, daddr_t);
static daddr_t ffs_hashalloc(struct inode *, int, daddr_t, int,
daddr_t (*)(struct inode *, int, daddr_t, int));
static int32_t ffs_mapsearch(struct fs *, struct cg *, daddr_t, int);
/*
* Allocate a block in the file system.
*
* The size of the requested block is given, which must be some
* multiple of fs_fsize and <= fs_bsize.
* A preference may be optionally specified. If a preference is given
* the following hierarchy is used to allocate a block:
* 1) allocate the requested block.
* 2) allocate a rotationally optimal block in the same cylinder.
* 3) allocate a block in the same cylinder group.
* 4) quadradically rehash into other cylinder groups, until an
* available block is located.
* If no block preference is given the following hierarchy is used
* to allocate a block:
* 1) allocate a block in the cylinder group that contains the
* inode for the file.
* 2) quadradically rehash into other cylinder groups, until an
* available block is located.
*/
int
ffs_alloc(struct inode *ip, daddr_t lbn __unused, daddr_t bpref, int size,
daddr_t *bnp)
{
struct fs *fs = ip->i_fs;
daddr_t bno;
int cg;
*bnp = 0;
if (size > fs->fs_bsize || fragoff(fs, size) != 0) {
errx(1, "ffs_alloc: bad size: bsize %d size %d",
fs->fs_bsize, size);
}
if (size == fs->fs_bsize && fs->fs_cstotal.cs_nbfree == 0)
goto nospace;
if (bpref >= fs->fs_size)
bpref = 0;
if (bpref == 0)
cg = ino_to_cg(fs, ip->i_number);
else
cg = dtog(fs, bpref);
bno = ffs_hashalloc(ip, cg, bpref, size, ffs_alloccg);
if (bno > 0) {
if (ip->i_fs->fs_magic == FS_UFS1_MAGIC)
ip->i_ffs1_blocks += size / DEV_BSIZE;
else
ip->i_ffs2_blocks += size / DEV_BSIZE;
*bnp = bno;
return (0);
}
nospace:
return (ENOSPC);
}
/*
* Select the desired position for the next block in a file. The file is
* logically divided into sections. The first section is composed of the
* direct blocks. Each additional section contains fs_maxbpg blocks.
*
* If no blocks have been allocated in the first section, the policy is to
* request a block in the same cylinder group as the inode that describes
* the file. If no blocks have been allocated in any other section, the
* policy is to place the section in a cylinder group with a greater than
* average number of free blocks. An appropriate cylinder group is found
* by using a rotor that sweeps the cylinder groups. When a new group of
* blocks is needed, the sweep begins in the cylinder group following the
* cylinder group from which the previous allocation was made. The sweep
* continues until a cylinder group with greater than the average number
* of free blocks is found. If the allocation is for the first block in an
* indirect block, the information on the previous allocation is unavailable;
* here a best guess is made based upon the logical block number being
* allocated.
*
* If a section is already partially allocated, the policy is to
* contiguously allocate fs_maxcontig blocks. The end of one of these
* contiguous blocks and the beginning of the next is physically separated
* so that the disk head will be in transit between them for at least
* fs_rotdelay milliseconds. This is to allow time for the processor to
* schedule another I/O transfer.
*/
/* XXX ondisk32 */
daddr_t
ffs_blkpref_ufs1(struct inode *ip, daddr_t lbn, int indx, int32_t *bap)
{
struct fs *fs;
int cg;
int avgbfree, startcg;
fs = ip->i_fs;
if (indx % fs->fs_maxbpg == 0 || bap[indx - 1] == 0) {
if (lbn < NDADDR + NINDIR(fs)) {
cg = ino_to_cg(fs, ip->i_number);
return (fs->fs_fpg * cg + fs->fs_frag);
}
/*
* Find a cylinder with greater than average number of
* unused data blocks.
*/
if (indx == 0 || bap[indx - 1] == 0)
startcg =
ino_to_cg(fs, ip->i_number) + lbn / fs->fs_maxbpg;
else
startcg = dtog(fs,
ufs_rw32(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + 1);
startcg %= fs->fs_ncg;
avgbfree = fs->fs_cstotal.cs_nbfree / fs->fs_ncg;
for (cg = startcg; cg < fs->fs_ncg; cg++)
if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree)
return (fs->fs_fpg * cg + fs->fs_frag);
for (cg = 0; cg <= startcg; cg++)
if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree)
return (fs->fs_fpg * cg + fs->fs_frag);
return (0);
}
/*
* We just always try to lay things out contiguously.
*/
return ufs_rw32(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + fs->fs_frag;
}
daddr_t
ffs_blkpref_ufs2(struct inode *ip, daddr_t lbn, int indx, int64_t *bap)
{
struct fs *fs;
int cg;
int avgbfree, startcg;
fs = ip->i_fs;
if (indx % fs->fs_maxbpg == 0 || bap[indx - 1] == 0) {
if (lbn < NDADDR + NINDIR(fs)) {
cg = ino_to_cg(fs, ip->i_number);
return (fs->fs_fpg * cg + fs->fs_frag);
}
/*
* Find a cylinder with greater than average number of
* unused data blocks.
*/
if (indx == 0 || bap[indx - 1] == 0)
startcg =
ino_to_cg(fs, ip->i_number) + lbn / fs->fs_maxbpg;
else
startcg = dtog(fs,
ufs_rw64(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + 1);
startcg %= fs->fs_ncg;
avgbfree = fs->fs_cstotal.cs_nbfree / fs->fs_ncg;
for (cg = startcg; cg < fs->fs_ncg; cg++)
if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree) {
return (fs->fs_fpg * cg + fs->fs_frag);
}
for (cg = 0; cg < startcg; cg++)
if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree) {
return (fs->fs_fpg * cg + fs->fs_frag);
}
return (0);
}
/*
* We just always try to lay things out contiguously.
*/
return ufs_rw64(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + fs->fs_frag;
}
/*
* Implement the cylinder overflow algorithm.
*
* The policy implemented by this algorithm is:
* 1) allocate the block in its requested cylinder group.
* 2) quadradically rehash on the cylinder group number.
* 3) brute force search for a free block.
*
* `size': size for data blocks, mode for inodes
*/
/*VARARGS5*/
static daddr_t
ffs_hashalloc(struct inode *ip, int cg, daddr_t pref, int size,
daddr_t (*allocator)(struct inode *, int, daddr_t, int))
{
struct fs *fs;
daddr_t result;
int i, icg = cg;
fs = ip->i_fs;
/*
* 1: preferred cylinder group
*/
result = (*allocator)(ip, cg, pref, size);
if (result)
return (result);
/*
* 2: quadratic rehash
*/
for (i = 1; i < fs->fs_ncg; i *= 2) {
cg += i;
if (cg >= fs->fs_ncg)
cg -= fs->fs_ncg;
result = (*allocator)(ip, cg, 0, size);
if (result)
return (result);
}
/*
* 3: brute force search
* Note that we start at i == 2, since 0 was checked initially,
* and 1 is always checked in the quadratic rehash.
*/
cg = (icg + 2) % fs->fs_ncg;
for (i = 2; i < fs->fs_ncg; i++) {
result = (*allocator)(ip, cg, 0, size);
if (result)
return (result);
cg++;
if (cg == fs->fs_ncg)
cg = 0;
}
return (0);
}
/*
* Determine whether a block can be allocated.
*
* Check to see if a block of the appropriate size is available,
* and if it is, allocate it.
*/
static daddr_t
ffs_alloccg(struct inode *ip, int cg, daddr_t bpref, int size)
{
struct cg *cgp;
struct buf *bp;
daddr_t bno, blkno;
int error, frags, allocsiz, i;
struct fs *fs = ip->i_fs;
const int needswap = UFS_FSNEEDSWAP(fs);
if (fs->fs_cs(fs, cg).cs_nbfree == 0 && size == fs->fs_bsize)
return (0);
error = bread(ip->i_fd, ip->i_fs, fsbtodb(fs, cgtod(fs, cg)),
(int)fs->fs_cgsize, &bp);
if (error) {
brelse(bp);
return (0);
}
cgp = (struct cg *)bp->b_data;
if (!cg_chkmagic_swap(cgp, needswap) ||
(cgp->cg_cs.cs_nbfree == 0 && size == fs->fs_bsize)) {
brelse(bp);
return (0);
}
if (size == fs->fs_bsize) {
bno = ffs_alloccgblk(ip, bp, bpref);
bdwrite(bp);
return (bno);
}
/*
* check to see if any fragments are already available
* allocsiz is the size which will be allocated, hacking
* it down to a smaller size if necessary
*/
frags = numfrags(fs, size);
for (allocsiz = frags; allocsiz < fs->fs_frag; allocsiz++)
if (cgp->cg_frsum[allocsiz] != 0)
break;
if (allocsiz == fs->fs_frag) {
/*
* no fragments were available, so a block will be
* allocated, and hacked up
*/
if (cgp->cg_cs.cs_nbfree == 0) {
brelse(bp);
return (0);
}
bno = ffs_alloccgblk(ip, bp, bpref);
bpref = dtogd(fs, bno);
for (i = frags; i < fs->fs_frag; i++)
setbit(cg_blksfree_swap(cgp, needswap), bpref + i);
i = fs->fs_frag - frags;
ufs_add32(cgp->cg_cs.cs_nffree, i, needswap);
fs->fs_cstotal.cs_nffree += i;
fs->fs_cs(fs, cg).cs_nffree += i;
fs->fs_fmod = 1;
ufs_add32(cgp->cg_frsum[i], 1, needswap);
bdwrite(bp);
return (bno);
}
bno = ffs_mapsearch(fs, cgp, bpref, allocsiz);
for (i = 0; i < frags; i++)
clrbit(cg_blksfree_swap(cgp, needswap), bno + i);
ufs_add32(cgp->cg_cs.cs_nffree, -frags, needswap);
fs->fs_cstotal.cs_nffree -= frags;
fs->fs_cs(fs, cg).cs_nffree -= frags;
fs->fs_fmod = 1;
ufs_add32(cgp->cg_frsum[allocsiz], -1, needswap);
if (frags != allocsiz)
ufs_add32(cgp->cg_frsum[allocsiz - frags], 1, needswap);
blkno = cg * fs->fs_fpg + bno;
bdwrite(bp);
return blkno;
}
/*
* Allocate a block in a cylinder group.
*
* This algorithm implements the following policy:
* 1) allocate the requested block.
* 2) allocate a rotationally optimal block in the same cylinder.
* 3) allocate the next available block on the block rotor for the
* specified cylinder group.
* Note that this routine only allocates fs_bsize blocks; these
* blocks may be fragmented by the routine that allocates them.
*/
static daddr_t
ffs_alloccgblk(struct inode *ip, struct buf *bp, daddr_t bpref)
{
struct cg *cgp;
daddr_t blkno;
int32_t bno;
struct fs *fs = ip->i_fs;
const int needswap = UFS_FSNEEDSWAP(fs);
u_int8_t *blksfree_swap;
cgp = (struct cg *)bp->b_data;
blksfree_swap = cg_blksfree_swap(cgp, needswap);
if (bpref == 0 || (uint32_t)dtog(fs, bpref) != ufs_rw32(cgp->cg_cgx, needswap)) {
bpref = ufs_rw32(cgp->cg_rotor, needswap);
} else {
bpref = blknum(fs, bpref);
bno = dtogd(fs, bpref);
/*
* if the requested block is available, use it
*/
if (ffs_isblock(fs, blksfree_swap, fragstoblks(fs, bno)))
goto gotit;
}
/*
* Take the next available one in this cylinder group.
*/
bno = ffs_mapsearch(fs, cgp, bpref, (int)fs->fs_frag);
if (bno < 0)
return (0);
cgp->cg_rotor = ufs_rw32(bno, needswap);
gotit:
blkno = fragstoblks(fs, bno);
ffs_clrblock(fs, blksfree_swap, (long)blkno);
ffs_clusteracct(fs, cgp, blkno, -1);
ufs_add32(cgp->cg_cs.cs_nbfree, -1, needswap);
fs->fs_cstotal.cs_nbfree--;
fs->fs_cs(fs, ufs_rw32(cgp->cg_cgx, needswap)).cs_nbfree--;
fs->fs_fmod = 1;
blkno = ufs_rw32(cgp->cg_cgx, needswap) * fs->fs_fpg + bno;
return (blkno);
}
/*
* Free a block or fragment.
*
* The specified block or fragment is placed back in the
* free map. If a fragment is deallocated, a possible
* block reassembly is checked.
*/
void
ffs_blkfree(struct inode *ip, daddr_t bno, long size)
{
struct cg *cgp;
struct buf *bp;
int32_t fragno, cgbno;
int i, error, cg, blk, frags, bbase;
struct fs *fs = ip->i_fs;
const int needswap = UFS_FSNEEDSWAP(fs);
if (size > fs->fs_bsize || fragoff(fs, size) != 0 ||
fragnum(fs, bno) + numfrags(fs, size) > fs->fs_frag) {
errx(1, "blkfree: bad size: bno %lld bsize %d size %ld",
(long long)bno, fs->fs_bsize, size);
}
cg = dtog(fs, bno);
if (bno >= fs->fs_size) {
warnx("bad block %lld, ino %llu", (long long)bno,
(unsigned long long)ip->i_number);
return;
}
error = bread(ip->i_fd, ip->i_fs, fsbtodb(fs, cgtod(fs, cg)),
(int)fs->fs_cgsize, &bp);
if (error) {
brelse(bp);
return;
}
cgp = (struct cg *)bp->b_data;
if (!cg_chkmagic_swap(cgp, needswap)) {
brelse(bp);
return;
}
cgbno = dtogd(fs, bno);
if (size == fs->fs_bsize) {
fragno = fragstoblks(fs, cgbno);
if (!ffs_isfreeblock(fs, cg_blksfree_swap(cgp, needswap), fragno)) {
errx(1, "blkfree: freeing free block %lld",
(long long)bno);
}
ffs_setblock(fs, cg_blksfree_swap(cgp, needswap), fragno);
ffs_clusteracct(fs, cgp, fragno, 1);
ufs_add32(cgp->cg_cs.cs_nbfree, 1, needswap);
fs->fs_cstotal.cs_nbfree++;
fs->fs_cs(fs, cg).cs_nbfree++;
} else {
bbase = cgbno - fragnum(fs, cgbno);
/*
* decrement the counts associated with the old frags
*/
blk = blkmap(fs, cg_blksfree_swap(cgp, needswap), bbase);
ffs_fragacct_swap(fs, blk, cgp->cg_frsum, -1, needswap);
/*
* deallocate the fragment
*/
frags = numfrags(fs, size);
for (i = 0; i < frags; i++) {
if (isset(cg_blksfree_swap(cgp, needswap), cgbno + i)) {
errx(1, "blkfree: freeing free frag: block %lld",
(long long)(cgbno + i));
}
setbit(cg_blksfree_swap(cgp, needswap), cgbno + i);
}
ufs_add32(cgp->cg_cs.cs_nffree, i, needswap);
fs->fs_cstotal.cs_nffree += i;
fs->fs_cs(fs, cg).cs_nffree += i;
/*
* add back in counts associated with the new frags
*/
blk = blkmap(fs, cg_blksfree_swap(cgp, needswap), bbase);
ffs_fragacct_swap(fs, blk, cgp->cg_frsum, 1, needswap);
/*
* if a complete block has been reassembled, account for it
*/
fragno = fragstoblks(fs, bbase);
if (ffs_isblock(fs, cg_blksfree_swap(cgp, needswap), fragno)) {
ufs_add32(cgp->cg_cs.cs_nffree, -fs->fs_frag, needswap);
fs->fs_cstotal.cs_nffree -= fs->fs_frag;
fs->fs_cs(fs, cg).cs_nffree -= fs->fs_frag;
ffs_clusteracct(fs, cgp, fragno, 1);
ufs_add32(cgp->cg_cs.cs_nbfree, 1, needswap);
fs->fs_cstotal.cs_nbfree++;
fs->fs_cs(fs, cg).cs_nbfree++;
}
}
fs->fs_fmod = 1;
bdwrite(bp);
}
static int
scanc(u_int size, const u_char *cp, const u_char table[], int mask)
{
const u_char *end = &cp[size];
while (cp < end && (table[*cp] & mask) == 0)
cp++;
return (end - cp);
}
/*
* Find a block of the specified size in the specified cylinder group.
*
* It is a panic if a request is made to find a block if none are
* available.
*/
static int32_t
ffs_mapsearch(struct fs *fs, struct cg *cgp, daddr_t bpref, int allocsiz)
{
int32_t bno;
int start, len, loc, i;
int blk, field, subfield, pos;
int ostart, olen;
const int needswap = UFS_FSNEEDSWAP(fs);
/*
* find the fragment by searching through the free block
* map for an appropriate bit pattern
*/
if (bpref)
start = dtogd(fs, bpref) / NBBY;
else
start = ufs_rw32(cgp->cg_frotor, needswap) / NBBY;
len = howmany(fs->fs_fpg, NBBY) - start;
ostart = start;
olen = len;
loc = scanc((u_int)len,
(const u_char *)&cg_blksfree_swap(cgp, needswap)[start],
(const u_char *)fragtbl[fs->fs_frag],
(1 << (allocsiz - 1 + (fs->fs_frag % NBBY))));
if (loc == 0) {
len = start + 1;
start = 0;
loc = scanc((u_int)len,
(const u_char *)&cg_blksfree_swap(cgp, needswap)[0],
(const u_char *)fragtbl[fs->fs_frag],
(1 << (allocsiz - 1 + (fs->fs_frag % NBBY))));
if (loc == 0) {
errx(1,
"ffs_alloccg: map corrupted: start %d len %d offset %d %ld",
ostart, olen,
ufs_rw32(cgp->cg_freeoff, needswap),
(long)cg_blksfree_swap(cgp, needswap) - (long)cgp);
/* NOTREACHED */
}
}
bno = (start + len - loc) * NBBY;
cgp->cg_frotor = ufs_rw32(bno, needswap);
/*
* found the byte in the map
* sift through the bits to find the selected frag
*/
for (i = bno + NBBY; bno < i; bno += fs->fs_frag) {
blk = blkmap(fs, cg_blksfree_swap(cgp, needswap), bno);
blk <<= 1;
field = around[allocsiz];
subfield = inside[allocsiz];
for (pos = 0; pos <= fs->fs_frag - allocsiz; pos++) {
if ((blk & field) == subfield)
return (bno + pos);
field <<= 1;
subfield <<= 1;
}
}
errx(1, "ffs_alloccg: block not in map: bno %lld", (long long)bno);
return (-1);
}
/*
* Update the cluster map because of an allocation or free.
*
* Cnt == 1 means free; cnt == -1 means allocating.
*/
void
ffs_clusteracct(struct fs *fs, struct cg *cgp, int32_t blkno, int cnt)
{
int32_t *sump;
int32_t *lp;
u_char *freemapp, *mapp;
int i, start, end, forw, back, map, bit;
const int needswap = UFS_FSNEEDSWAP(fs);
if (fs->fs_contigsumsize <= 0)
return;
freemapp = cg_clustersfree_swap(cgp, needswap);
sump = cg_clustersum_swap(cgp, needswap);
/*
* Allocate or clear the actual block.
*/
if (cnt > 0)
setbit(freemapp, blkno);
else
clrbit(freemapp, blkno);
/*
* Find the size of the cluster going forward.
*/
start = blkno + 1;
end = start + fs->fs_contigsumsize;
if ((unsigned)end >= ufs_rw32(cgp->cg_nclusterblks, needswap))
end = ufs_rw32(cgp->cg_nclusterblks, needswap);
mapp = &freemapp[start / NBBY];
map = *mapp++;
bit = 1 << (start % NBBY);
for (i = start; i < end; i++) {
if ((map & bit) == 0)
break;
if ((i & (NBBY - 1)) != (NBBY - 1)) {
bit <<= 1;
} else {
map = *mapp++;
bit = 1;
}
}
forw = i - start;
/*
* Find the size of the cluster going backward.
*/
start = blkno - 1;
end = start - fs->fs_contigsumsize;
if (end < 0)
end = -1;
mapp = &freemapp[start / NBBY];
map = *mapp--;
bit = 1 << (start % NBBY);
for (i = start; i > end; i--) {
if ((map & bit) == 0)
break;
if ((i & (NBBY - 1)) != 0) {
bit >>= 1;
} else {
map = *mapp--;
bit = 1 << (NBBY - 1);
}
}
back = start - i;
/*
* Account for old cluster and the possibly new forward and
* back clusters.
*/
i = back + forw + 1;
if (i > fs->fs_contigsumsize)
i = fs->fs_contigsumsize;
ufs_add32(sump[i], cnt, needswap);
if (back > 0)
ufs_add32(sump[back], -cnt, needswap);
if (forw > 0)
ufs_add32(sump[forw], -cnt, needswap);
/*
* Update cluster summary information.
*/
lp = &sump[fs->fs_contigsumsize];
for (i = fs->fs_contigsumsize; i > 0; i--)
if (ufs_rw32(*lp--, needswap) > 0)
break;
fs->fs_maxcluster[ufs_rw32(cgp->cg_cgx, needswap)] = i;
}