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block: Reuse bs as backing hd for drive-backup sync=none 

Opening the backing image for the second time is bad, especially here
when it is also in use as the active image as the source. The
drive-backup job itself doesn't read from target->backing for COW,
instead it gets data from the write notifier, so it's not a big problem.
However, exporting the target to NBD etc. won't work, because of the
likely stale metadata cache.

Use BDRV_O_NO_BACKING in this case and manually set up the backing
BdrvChild.

Cc: qemu-stable@nongnu.org
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2017-05-03 00:35:53 +08:00 committed by Kevin Wolf
parent 9c77fec2d3
commit fc0932fdcf
1 changed files with 14 additions and 1 deletions
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15
blockdev.c
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@ -3151,6 +3151,7 @@ static BlockJob *do_drive_backup(DriveBackup *backup, BlockJobTxn *txn,
Error *local_err = NULL;
int flags;
int64_t size;
bool set_backing_hd = false;
if (!backup->has_speed) {
backup->speed = 0;
@ -3201,6 +3202,8 @@ static BlockJob *do_drive_backup(DriveBackup *backup, BlockJobTxn *txn,
}
if (backup->sync == MIRROR_SYNC_MODE_NONE) {
source = bs;
flags |= BDRV_O_NO_BACKING;
set_backing_hd = true;
}
size = bdrv_getlength(bs);
@ -3227,7 +3230,9 @@ static BlockJob *do_drive_backup(DriveBackup *backup, BlockJobTxn *txn,
}
if (backup->format) {
options = qdict_new();
if (!options) {
options = qdict_new();
}
qdict_put_str(options, "driver", backup->format);
}
@ -3238,6 +3243,14 @@ static BlockJob *do_drive_backup(DriveBackup *backup, BlockJobTxn *txn,
bdrv_set_aio_context(target_bs, aio_context);
if (set_backing_hd) {
bdrv_set_backing_hd(target_bs, source, &local_err);
if (local_err) {
bdrv_unref(target_bs);
goto out;
}
}
if (backup->has_bitmap) {
bmap = bdrv_find_dirty_bitmap(bs, backup->bitmap);
if (!bmap) {