If a reference count is not representable with the current refcount order, the image check should point to qemu-img amend for increasing the refcount order. However, qemu-img amend needs write access to the image which cannot be provided if the image is marked corrupt; and the image check will not mark the image consistent unless everything actually is consistent.
Therefore, if an image is marked corrupt and the image check encounters a reference count overflow, it cannot be fixed by using qemu-img amend to increase the refcount order. Instead, one has to use qemu-img convert to create a completely new copy of the image in this case. Alternatively, we may want to give the user a way of manually removing the corrupt flag, maybe through qemu-img amend, but this is not part of this patch. Signed-off-by: Max Reitz <mre...@redhat.com> Reviewed-by: Eric Blake <ebl...@redhat.com> --- block/qcow2-refcount.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index b59a028..e9647ce 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -1368,6 +1368,9 @@ static int inc_refcounts(BlockDriverState *bs, if (refcount == s->refcount_max) { fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64 "\n", cluster_offset); + fprintf(stderr, "Use qemu-img amend to increase the refcount entry " + "width or qemu-img convert to create a clean copy if the " + "image cannot be opened for writing\n"); res->corruptions++; continue; } -- 1.9.3