On 22.12.19 12:36, Alberto Garcia wrote: > This patch adds QCow2SubclusterType, which is the subcluster-level > version of QCow2ClusterType. All QCOW2_SUBCLUSTER_* values have the > the same meaning as their QCOW2_CLUSTER_* equivalents (when they > exist). See below for details and caveats. > > In images without extended L2 entries clusters are treated as having > exactly one subcluster so it is possible to replace one data type with > the other while keeping the exact same semantics. > > With extended L2 entries there are new possible values, and every > subcluster in the same cluster can obviously have a different > QCow2SubclusterType so functions need to be adapted to work on the > subcluster level. > > There are several things that have to be taken into account: > > a) QCOW2_SUBCLUSTER_COMPRESSED means that the whole cluster is > compressed. We do not support compression at the subcluster > level. > > b) There are two different values for unallocated subclusters: > QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN which means that the whole > cluster is unallocated, and QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC > which means that the cluster is allocated but the subcluster is > not. The latter can only happen in images with extended L2 > entries. > > c) QCOW2_SUBCLUSTER_INVALID is used to detect the cases where an L2 > entry has a value that violates the specification. 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_SUBCLUSTER_INVALID is only returned for images > with extended L2 entries. > > qcow2_cluster_to_subcluster_type() is added as a separate function > from qcow2_get_subcluster_type(), but this is only temporary and both > will be merged in a subsequent patch. > > Signed-off-by: Alberto Garcia <be...@igalia.com> > --- > block/qcow2.h | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 92 insertions(+)
With the comment style fixed as now required by the coding style (/* and */ on separate lines), and regardless of the bit ordering: Reviewed-by: Max Reitz <mre...@redhat.com>
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