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Lunev wrote: > From: Denis V. Lunev > > discard_l2_subclusters() passes the discarded range down to the host > file even when the cluster is still referenced by an internal snapshot. > The active L2 table is copied before it is changed, so the snapshot > metadata stays correct, but the host range under it is punched out and > the snapshot reads zeroes there afterwards. qemu-img check finds nothing > wrong. > > Pass the discard down only for a cluster with QCOW_OFLAG_COPIED set, > i.e. one owned by the active layer alone. A shared cluster gets only > its active L2 bitmap updated, as a whole-cluster discard already does > by dropping the refcount instead of punching the host file. > > Cover it in iotest 271. > > Fixes: 225b4de1249 ("qcow2: make subclusters discardable") > Signed-off-by: Denis V. Lunev > --- > [...] Reviewed-by: Andrey Drobyshev