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[Qemu-devel] [PATCH 1/3] cow: use pread/pwrite
From: |
Christoph Hellwig |
Subject: |
[Qemu-devel] [PATCH 1/3] cow: use pread/pwrite |
Date: |
Fri, 7 May 2010 17:17:09 +0200 |
User-agent: |
Mutt/1.3.28i |
Use pread/pwrite instead of lseek + read/write in preparation of using the
qemu block API.
Signed-off-by: Christoph Hellwig <address@hidden>
Index: qemu/block/cow.c
===================================================================
--- qemu.orig/block/cow.c 2010-05-04 19:11:24.897004616 +0200
+++ qemu/block/cow.c 2010-05-04 19:12:29.010255070 +0200
@@ -78,7 +78,7 @@ static int cow_open(BlockDriverState *bs
}
s->fd = fd;
/* 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;
}
@@ -159,8 +159,8 @@ static int cow_read(BlockDriverState *bs
while (nb_sectors > 0) {
if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
- lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
- ret = read(s->fd, buf, n * 512);
+ ret = pread(s->fd, buf, n * 512,
+ s->cow_sectors_offset + sector_num * 512);
if (ret != n * 512)
return -1;
} else {
@@ -186,8 +186,8 @@ static int cow_write(BlockDriverState *b
BDRVCowState *s = bs->opaque;
int ret, i;
- lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
- ret = write(s->fd, buf, nb_sectors * 512);
+ ret = pwrite(s->fd, buf, nb_sectors * 512,
+ s->cow_sectors_offset + sector_num * 512);
if (ret != nb_sectors * 512)
return -1;
for (i = 0; i < nb_sectors; i++)