On 28.06.20 13:02, Alberto Garcia wrote: > The offset field of an uncompressed cluster's L2 entry must be aligned > to the cluster size, otherwise it is invalid. If the cluster has no > data then it means that the offset points to a preallocation, so we > can clear the offset field without affecting the guest-visible data. > This is what 'qemu-img check' does when run in repair mode. > > On traditional qcow2 images this can only happen when QCOW_OFLAG_ZERO > is set, and repairing such entries turns the clusters from ZERO_ALLOC > into ZERO_PLAIN. > > Extended L2 entries have no ZERO_ALLOC clusters and no QCOW_OFLAG_ZERO > but the idea is the same: if none of the subclusters are allocated > then we can clear the offset field and leave the bitmap untouched. > > Signed-off-by: Alberto Garcia <[email protected]> > --- > block/qcow2-refcount.c | 16 +++++++++++----- > tests/qemu-iotests/060.out | 2 +- > 2 files changed, 12 insertions(+), 6 deletions(-)
Reviewed-by: Max Reitz <[email protected]>
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