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qemu-img rebase: Fix for undersized backing files 

Backing files may be smaller than the corresponding COW file. When
reading directly from the backing file, qemu-img rebase must consider
this and assume zero sectors after the end of backing files.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
This commit is contained in:
Kevin Wolf 2011-12-07 12:42:10 +01:00
parent b9c532903f
commit 87a1b3e381
1 changed files with 33 additions and 9 deletions
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42
qemu-img.c
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@ -1420,6 +1420,8 @@ static int img_rebase(int argc, char **argv)
*/
if (!unsafe) {
uint64_t num_sectors;
uint64_t old_backing_num_sectors;
uint64_t new_backing_num_sectors;
uint64_t sector;
int n;
uint8_t * buf_old;
@ -1430,6 +1432,8 @@ static int img_rebase(int argc, char **argv)
buf_new = qemu_blockalign(bs, IO_BUF_SIZE);
bdrv_get_geometry(bs, &num_sectors);
bdrv_get_geometry(bs_old_backing, &old_backing_num_sectors);
bdrv_get_geometry(bs_new_backing, &new_backing_num_sectors);
local_progress = (float)100 /
(num_sectors / MIN(num_sectors, IO_BUF_SIZE / 512));
@ -1448,16 +1452,36 @@ static int img_rebase(int argc, char **argv)
continue;
}
/* Read old and new backing file */
ret = bdrv_read(bs_old_backing, sector, buf_old, n);
if (ret < 0) {
error_report("error while reading from old backing file");
goto out;
/*
* Read old and new backing file and take into consideration that
* backing files may be smaller than the COW image.
*/
if (sector >= old_backing_num_sectors) {
memset(buf_old, 0, n * BDRV_SECTOR_SIZE);
} else {
if (sector + n > old_backing_num_sectors) {
n = old_backing_num_sectors - sector;
}
ret = bdrv_read(bs_old_backing, sector, buf_old, n);
if (ret < 0) {
error_report("error while reading from old backing file");
goto out;
}
}
ret = bdrv_read(bs_new_backing, sector, buf_new, n);
if (ret < 0) {
error_report("error while reading from new backing file");
goto out;
if (sector >= new_backing_num_sectors) {
memset(buf_new, 0, n * BDRV_SECTOR_SIZE);
} else {
if (sector + n > new_backing_num_sectors) {
n = new_backing_num_sectors - sector;
}
ret = bdrv_read(bs_new_backing, sector, buf_new, n);
if (ret < 0) {
error_report("error while reading from new backing file");
goto out;
}
}
/* If they differ, we need to write to the COW file */