Re: [libvirt PATCH v2 2/2] storage_file: add support to probe cluster_size from QCOW2 images

>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; --- Changes in v2: - Reworkded to use callback. src/storage/storage_util.c | 3 ++ src/storage_file/storage_file_probe.c | 70 ++++++++++++++++++++------- 2 files changed, 56 insertions(+), 17 deletions(-)

@@ -468,6 +477,28 @@ qcow2GetExtensions(const char *buf, } +static unsigned long long +qcow2GetClusterSize(const char *buf, + size_t buf_size, + int endian)

+{ + int clusterBits = 0; + + if ((QCOWX_HDR_CLUSTER_BITS_OFFSET + 4) > buf_size) + return 0; + + if (endian == LV_LITTLE_ENDIAN) + clusterBits = virReadBufInt32LE(buf + QCOWX_HDR_CLUSTER_BITS_OFFSET); + else + clusterBits = virReadBufInt32BE(buf + QCOWX_HDR_CLUSTER_BITS_OFFSET); + + if (clusterBits > 0) + return 1 << clusterBits; + + return 0; +}