On 04.11.19 13:35, Max Reitz wrote: > On 26.10.19 23:25, Alberto Garcia wrote: >> This function returns the type of an individual subcluster. If an >> image does not have subclusters then this returns the exact same value >> as qcow2_get_cluster_type(). >> >> The information in standard and extended L2 entries is encoded in a >> slightly different way, but all existing QCow2ClusterType values are >> also valid for subclusters and have the same meanings (although they >> typically only apply to the requested subcluster). >> >> There are two important exceptions to this: >> >> a) QCOW2_CLUSTER_COMPRESSED means that the whole cluster is >> compressed. We do not support compression at the subcluster >> level. >> >> b) QCOW2_CLUSTER_UNALLOCATED means that the cluster is unallocated, >> that is, the offset field of the L2 entry does not point to a >> host cluster. All subclusters are obviously unallocated too but >> any of them could be of type QCOW2_CLUSTER_ZERO_PLAIN. >> >> In addition to that, extended L2 entries allow one new scenario where >> the cluster is normally allocated but an individual subcluster is not. >> This is very different from (b) and because of that this patch adds a >> new value called QCOW2_CLUSTER_UNALLOCATED_SUBCLUSTER. >> >> As a last thing, this patch adds QCOW2_CLUSTER_INVALID to detect the >> cases where an L2 entry has a value that violates the spec. The caller >> is responsible for handling these situations. >> >> To prevent compatibility problems with images that have invalid values >> but are currently being read by QEMU without causing side effects, >> QCOW2_CLUSTER_INVALID is only returned for images with extended L2 >> entries. >> >> Signed-off-by: Alberto Garcia <be...@igalia.com> >> --- >> block/qcow2.h | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 62 insertions(+) > > [...] > >> + case QCOW2_CLUSTER_ZERO_PLAIN: >> + case QCOW2_CLUSTER_ZERO_ALLOC: >> + return QCOW2_CLUSTER_INVALID; > > The spec doesn’t say anything about this, though.
It does, I just forgot. O:-) Max
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