Re: [PATCH] audio: Never send migration section

[Daniel P . Berrangé]

On Mon, Aug 09, 2021 at 06:09:56PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The audio migration vmstate is empty, and always has been; we can't
> just remove it though because an old qemu might send it us.
> Changes with -audiodev now mean it's sometimes created when it didn't
> used to be, and can confuse migration to old qemu.
> 
> Change it so that vmstate_audio is never sent; if it's received it
> should still be accepted, and old qemu's shouldn't be too upset if it's
> missing.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  audio/audio.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>


For testing I have a VM with -audiodev, but *WITHOUT* any sound
frontend devices. Live migrating to a QEMU using QEMU_AUDIO_DRV
would previously fail. With this applied it now works, showing
that we dont uncessarily send this.

I also tested migration to a QEMU with -audiodev, but without
this patch, and that still works as before, showing that QEMU
is happy if this section is not sent.

> 
> diff --git a/audio/audio.c b/audio/audio.c
> index 59453ef856..54a153c0ef 100644
> --- a/audio/audio.c
> +++ b/audio/audio.c
> @@ -1622,10 +1622,20 @@ void audio_cleanup(void)
>      }
>  }
>  
> +static bool vmstate_audio_needed(void *opaque)
> +{
> +    /*
> +     * Never needed, this vmstate only exists in case
> +     * an old qemu sends it to us.
> +     */
> +    return false;
> +}
> +
>  static const VMStateDescription vmstate_audio = {
>      .name = "audio",
>      .version_id = 1,
>      .minimum_version_id = 1,
> +    .needed = vmstate_audio_needed,
>      .fields = (VMStateField[]) {
>          VMSTATE_END_OF_LIST()
>      }
> -- 
> 2.31.1
> 

Regards,
Daniel
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