Re: [Qemu-devel] [PATCH v2 07/16] qcow2: Write v3-compliant snapshot list on upgrade

[Eric Blake <eblake@redhat.com>]

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On 8/19/19 1:55 PM, Max Reitz wrote:
> qcow2 v3 requires every snapshot table entry to have two extra data
> fields: The 64-bit VM state size, and the virtual disk size.  Both are
> optional for v2 images, so they may not be present.
> 
> qcow2_upgrade() therefore should update the snapshot table to ensure all
> entries have these extra data fields.
> 
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1727347
> Reported-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 

> @@ -4768,7 +4770,33 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
>      /* There are no other versions (yet) that you can upgrade to */
>      assert(target_version == 3);
>  
> -    status_cb(bs, 0, 1, cb_opaque);
> +    status_cb(bs, 0, 2, cb_opaque);
> +
> +    /*
> +     * In v2, snapshots do not need to have extra data.  v3 requires
> +     * the 64-bit VM state size and the virtual disk size to be
> +     * present.
> +     * qcow2_write_snapshots() will always write the list in the
> +     * v3-compliant format.
> +     */
> +    need_snapshot_update = false;
> +    for (i = 0; i < s->nb_snapshots; i++) {
> +        if (s->snapshots[i].extra_data_size <
> +            sizeof_field(QCowSnapshotExtraData, vm_state_size_large) +
> +            sizeof_field(QCowSnapshotExtraData, disk_size))

sizeof(extra) would be more concise than two sizeof_field() added
together, but might cause problems if we later expand the size of extra
for other reasons, but don't revisit this code.  So I actually like what
you did here.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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