[libvirt PATCH v2 2/2] storage_file: add support to probe cluster_size from QCOW2 images
John Ferlan
jferlan at redhat.com
Sat May 22 13:23:38 UTC 2021
On 5/20/21 11:14 AM, 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 at redhat.com>
> ---
>
> 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(-)
>
[...]
>
> +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;
> +
Coverity showed me a new error today: OVERFLOW_BEFORE_WIDEN
1) Event overflow_before_widen: Potentially overflowing expression "1 <<
clusterBits" with type "int" (32 bits, signed) is evaluated using 32-bit
arithmetic, and then used in a context that expects an expression of
type "unsigned long long" (64 bits, unsigned).
(2) Event remediation: To avoid overflow, cast "1" to type "unsigned
long long".
John
> + return 0;
> +}
> +
> +
[...]
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