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qcow2: Update snapshot table information at once 

Failing in the middle wouldn't help with the integrity of the image, so
doing everything in a single request seems better.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
This commit is contained in:
Kevin Wolf 2011-11-18 18:27:00 +01:00
parent 07fd877900
commit d69969c404
1 changed files with 10 additions and 12 deletions
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22
block/qcow2-snapshot.c
View File

@ -137,8 +137,10 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
QCowSnapshot *sn;
QCowSnapshotHeader h;
int i, name_size, id_str_size, snapshots_size;
uint64_t data64;
uint32_t data32;
struct {
uint32_t nb_snapshots;
uint64_t snapshots_offset;
} QEMU_PACKED header_data;
int64_t offset, snapshots_offset;
int ret;
@ -200,24 +202,20 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
/*
* Update the header to point to the new snapshot table. This requires the
* new table and its refcounts to be stable on disk.
*
* FIXME This should be done with a single write
*/
ret = bdrv_flush(bs);
if (ret < 0) {
goto fail;
}
data64 = cpu_to_be64(snapshots_offset);
ret = bdrv_pwrite(bs->file, offsetof(QCowHeader, snapshots_offset),
&data64, sizeof(data64));
if (ret < 0) {
goto fail;
}
QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
header_data.nb_snapshots = cpu_to_be32(s->nb_snapshots);
header_data.snapshots_offset = cpu_to_be64(snapshots_offset);
data32 = cpu_to_be32(s->nb_snapshots);
ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
&data32, sizeof(data32));
&header_data, sizeof(header_data));
if (ret < 0) {
goto fail;
}