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cow: use pread/pwrite

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Use pread/pwrite instead of lseek + read/write in preparation of using the
qemu block API.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Christoph Hellwig 2010-06-07 12:06:28 +02:00 • committed by Kevin Wolf
parent 68dba0bf45
commit 122bb9e32d
1 changed files with 5 additions and 5 deletions
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10
block/cow.c
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@ -78,7 +78,7 @@ static int cow_open(BlockDriverState *bs, const char *filename, int flags)
} }
s->fd = fd; s->fd = fd;
/* see if it is a cow image */ /* see if it is a cow image */
if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) { if (pread(fd, &cow_header, sizeof(cow_header), 0) != sizeof(cow_header)) {
goto fail; goto fail;
} }
@ -159,8 +159,8 @@ static int cow_read(BlockDriverState *bs, int64_t sector_num,
while (nb_sectors > 0) { while (nb_sectors > 0) {
if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) { if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET); ret = pread(s->fd, buf, n * 512,
ret = read(s->fd, buf, n * 512); s->cow_sectors_offset + sector_num * 512);
if (ret != n * 512) if (ret != n * 512)
return -1; return -1;
} else { } else {
@ -186,8 +186,8 @@ static int cow_write(BlockDriverState *bs, int64_t sector_num,
BDRVCowState *s = bs->opaque; BDRVCowState *s = bs->opaque;
int ret, i; int ret, i;
lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET); ret = pwrite(s->fd, buf, nb_sectors * 512,
ret = write(s->fd, buf, nb_sectors * 512); s->cow_sectors_offset + sector_num * 512);
if (ret != nb_sectors * 512) if (ret != nb_sectors * 512)
return -1; return -1;
for (i = 0; i < nb_sectors; i++) for (i = 0; i < nb_sectors; i++)