Re: [Qemu-devel] [RFC PATCH 07/17] qcow2: introduce icount field for snapshots

[Eric Blake]

On 04/25/2018 07:46 AM, Pavel Dovgalyuk wrote:
> This patch introduces the icount field for saving within the snapshot.
> It is required for navigation between the snapshots in record/replay mode.
> 
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> ---
>  block/qcow2-snapshot.c |    9 +++++++++
>  block/qcow2.h          |    2 ++
>  2 files changed, 11 insertions(+)

Missing a change to docs/interop/qcow2.txt.  You cannot add new features
into the qcow2 internal snapshot metadata without first documenting them
as part of the qcow2 spec.

> 
> diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
> index 74293be..4f2357e 100644
> --- a/block/qcow2-snapshot.c
> +++ b/block/qcow2-snapshot.c
> @@ -103,6 +103,12 @@ int qcow2_read_snapshots(BlockDriverState *bs)
>              sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
>          }
>  
> +        if (extra_data_size >= 24) {
> +            sn->icount = be64_to_cpu(extra.icount);

That's VERY dangerous without a spec change.  If someone else adds extra
data in some other format, then you will misinterpret their extra
information as your icount information.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

signature.asc
Description: OpenPGP digital signature