Re: [libvirt PATCH 2/2] storage_file: add support to probe cluster_size from QCOW2 images

On Thu, May 13, 2021 at 13:23:05 +0200, Pavel Hrdina wrote: > >From QEMU docs/interop/qcow2.txt : > > Byte 20 - 23: cluster_bits > Number of bits that are used for addressing an offset > within a cluster (1 << cluster_bits is the cluster size). > > With this patch libvirt will be able to report the current cluster_size > for all existing storage volumes managed by storage driver. > > Signed-off-by: Pavel Hrdina <phrdina(a)redhat.com&gt; > --- > src/storage/storage_util.c | 3 ++ > src/storage_file/storage_file_probe.c | 55 +++++++++++++++++++-------- > 2 files changed, 42 insertions(+), 16 deletions(-) [...] > diff --git a/src/storage_file/storage_file_probe.c b/src/storage_file/storage_file_probe.c > index afe64da02e..423597049f 100644 > --- a/src/storage_file/storage_file_probe.c > +++ b/src/storage_file/storage_file_probe.c > @@ -94,6 +94,9 @@ struct FileTypeInfo { > /* Store a COW base image path (possibly relative), > * or NULL if there is no COW base image, to RES; > * return BACKING_STORE_* */ > + int clusterBitsOffset; /* Byte offset from start of file where we find > + * number of cluster bits, -1 to skip. */ > + int clusterBitsSize; /* Number of bytes for cluster bits. */ This isn't actually used [1].

> const struct FileEncryptionInfo *cryptInfo; /* Encryption info */ > int (*getBackingStore)(char **res, int *format, > const char *buf, size_t buf_size); Given how the value is stored in the header it seems that it won't really be usable for any other format. I think we should parse it via a callback rather than the generic offset/size parser. Specifically since the cluster size is stored as number of bits.