Re: [PATCH] vhost-user: Silence unsupported VHOST_USER_PROTOCOL_F_RARP error

[Stefano Garzarella]

On Tue, Jan 21, 2025 at 11:00:29AM +0100, Laurent Vivier wrote:
> In vhost_user_receive() if vhost_net_notify_migration_done() reports
> an error we display on the console:
>
>  Vhost user backend fails to broadcast fake RARP
>
> This message can be useful if there is a problem to execute
> VHOST_USER_SEND_RARP but it is useless if the backend doesn't
> support VHOST_USER_PROTOCOL_F_RARP.
>
> Don't report the error if vhost_net_notify_migration_done()
> returns -ENOTSUP (from vhost_user_migration_done())
>
> Update vhost_net-stub.c to return -ENOTSUP too.
>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> hw/net/vhost_net-stub.c | 2 +-
> net/vhost-user.c        | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/vhost_net-stub.c b/hw/net/vhost_net-stub.c
> index 72df6d757e4d..875cd6c2b9c8 100644
> --- a/hw/net/vhost_net-stub.c
> +++ b/hw/net/vhost_net-stub.c
> @@ -93,7 +93,7 @@ void vhost_net_config_mask(VHostNetState *net, VirtIODevice 
> *dev, bool mask)
>
> int vhost_net_notify_migration_done(struct vhost_net *net, char* mac_addr)
> {
> -    return -1;
> +    return -ENOTSUP;
> }
>
> VHostNetState *get_vhost_net(NetClientState *nc)
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 12555518e838..636fff8a84a2 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -146,7 +146,7 @@ static ssize_t vhost_user_receive(NetClientState *nc, const 
> uint8_t *buf,
>
>         r = vhost_net_notify_migration_done(s->vhost_net, mac_addr);
>
> -        if ((r != 0) && (display_rarp_failure)) {
> +        if ((r != 0) && (r != -ENOTSUP) && (display_rarp_failure)) {
>             fprintf(stderr,
>                     "Vhost user backend fails to broadcast fake RARP\n");
>             fflush(stderr);
> --
> 2.47.1

IIUC the message was there since the introduction about 10 years ago
from commit 3e866365e1 ("vhost user: add rarp sending after live
migration for legacy guest"). IIUC -ENOTSUP is returned when both F_RARP
and F_GUEST_ANNOUNCE are not negotiated.

That said, I honestly don't know what F_RARP or F_GUEST_ANNOUNCE is for,
but my understanding is that the message was to notify that the
migration was finished (reading that commit).

If neither feature is supported, could this be a problem for the user
and that's why we were printing the message?

Thanks,
Stefano