Re: [PATCH 02/13] qcow2: introduce icount field for snapshots

[Eric Blake <eblake@redhat.com>]

On 6/26/20 5:19 AM, Pavel Dovgalyuk wrote:
> From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> 
> 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 <Pavel.Dovgalyuk@ispras.ru>
> Acked-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   0 files changed
> 

That's an odd diffstat; you may want to investigate why git isn't 
showing the usual diffstat that makes it easier to see which files are 
touched and the relative size of the changes.


> +++ b/docs/interop/qcow2.txt
> @@ -645,6 +645,11 @@ Snapshot table entry:
>   
>                       Byte 48 - 55:   Virtual disk size of the snapshot in bytes
>   
> +                    Byte 56 - 63:   icount value which corresponds to
> +                                    the record/replay instruction count
> +                                    when the snapshot was taken. Set to -1
> +                                    if icount was disabled
> +
>                       Version 3 images must include extra data at least up to
>                       byte 55.

Should we have additional text here, similar to what was added to the 
overall header in 3ae3fcfa, about how to properly add additional 
optional fields while maintaining back-compat considerations?  Maybe 
just a one sentence reference that the rules in that section apply here too?

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