| Message ID | 20190920152804.12875-2-mreitz@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Fix check_to_replace_node() | expand |
20.09.2019 18:27, Max Reitz wrote: > There is no good reason why we would allow external snapshots only on > the first non-filter node in a chain. Parent BDSs should not care > whether their child is replaced by a snapshot. (If they do care, they > should announce that via freezing the chain, which is checked in > bdrv_append() through bdrv_set_backing_hd().) > > Before we had bdrv_is_first_non_filter() here (since 212a5a8f095), there > was a special function bdrv_check_ext_snapshot() that allowed snapshots > by default, but block drivers could override this. Only blkverify did > so, however. > > It is not clear to me why blkverify would do so; maybe just so that the > testee block driver would not be replaced. The introducing commit > f6186f49e2c does not explain why. Maybe because 08b24cfe376 would have > been the correct solution? (Which adds a .supports_backing check.) > > Signed-off-by: Max Reitz<mreitz@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
diff --git a/blockdev.c b/blockdev.c index f89e48fc79..b62b33dc03 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1596,11 +1596,6 @@ static void external_snapshot_prepare(BlkActionState *common, } } - if (!bdrv_is_first_non_filter(state->old_bs)) { - error_setg(errp, QERR_FEATURE_DISABLED, "snapshot"); - goto out; - } - if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) { BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data; const char *format = s->has_format ? s->format : "qcow2";
There is no good reason why we would allow external snapshots only on the first non-filter node in a chain. Parent BDSs should not care whether their child is replaced by a snapshot. (If they do care, they should announce that via freezing the chain, which is checked in bdrv_append() through bdrv_set_backing_hd().) Before we had bdrv_is_first_non_filter() here (since 212a5a8f095), there was a special function bdrv_check_ext_snapshot() that allowed snapshots by default, but block drivers could override this. Only blkverify did so, however. It is not clear to me why blkverify would do so; maybe just so that the testee block driver would not be replaced. The introducing commit f6186f49e2c does not explain why. Maybe because 08b24cfe376 would have been the correct solution? (Which adds a .supports_backing check.) Signed-off-by: Max Reitz <mreitz@redhat.com> --- blockdev.c | 5 ----- 1 file changed, 5 deletions(-)