When loading an internal snapshot whose L1 table is smaller than the current L1 table, the size of the current L1 would be shrunk to the snapshot's L1 size in memory, but not on disk. This lead to incorrect refcount updates and eventuelly to image corruption.
Instead of writing the new L1 size to disk, this simply retains the bigger L1 size that is currently in use and makes sure that the unused part is zeroed. Signed-off-by: Kevin Wolf <kw...@redhat.com> --- Philipp, I think this should fix your corruption. Please give it a try. Anthony, this must go into 0.15. Given the short time until -rc2, do you prefer to pick it up directly or should I send a pull request tomorrow? The patch looks obvious, is tested with the given testcase and survives a basic qemu-iotests run (though qemu-iotests doesn't exercise snapshots a lot) Stefan, please review :-) block/qcow2-snapshot.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c index 74823a5..4a8868a 100644 --- a/block/qcow2-snapshot.c +++ b/block/qcow2-snapshot.c @@ -330,8 +330,9 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id) if (qcow2_grow_l1_table(bs, sn->l1_size, true) < 0) goto fail; - s->l1_size = sn->l1_size; + memset(s->l1_table + sn->l1_size, 0, s->l1_size - sn->l1_size); l1_size2 = s->l1_size * sizeof(uint64_t); + /* copy the snapshot l1 table to the current l1 table */ if (bdrv_pread(bs->file, sn->l1_table_offset, s->l1_table, l1_size2) != l1_size2) -- 1.7.6