netdev - Re: [PATCH RFC 2/2] virtio_net: enable probing for NEEDS

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Date:   Tue, 29 Aug 2017 23:16:58 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC 2/2] virtio_net: enable probing for NEEDS_RESET
 support

On Tue, Aug 29, 2017 at 04:07:59PM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> Implement a mechanism to signal that a virtio device implements the
> VIRTIO_CONFIG_S_NEEDS_RESET command.
> 
> Testing for VIRTIO_CONFIG_S_NEEDS_RESET support by issuing the request
> and verifying the reset state would require an expensive state change.
> 
> To avoid that, add a status bit to the feature register used during
> feature negotiation between host and guest.
> 
> Set the bit for virtio-net, which supports the feature.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

All virtio 1 devices have the reset feature so maybe guest does
not need this flag. Does device need it? Does device really
care that guest can't recover?

> ---
>  drivers/net/virtio_net.c           | 2 ++
>  include/uapi/linux/virtio_config.h | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5e349226f7c1..15483a982106 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2801,12 +2801,14 @@ static struct virtio_device_id id_table[] = {
>  
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> +	VIRTIO_F_CAN_RESET,
>  };
>  
>  static unsigned int features_legacy[] = {
>  	VIRTNET_FEATURES,
>  	VIRTIO_NET_F_GSO,
>  	VIRTIO_F_ANY_LAYOUT,
> +	VIRTIO_F_CAN_RESET,
>  };
>  
>  static struct virtio_driver virtio_net_driver = {
> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> index 308e2096291f..726be44a04d3 100644
> --- a/include/uapi/linux/virtio_config.h
> +++ b/include/uapi/linux/virtio_config.h
> @@ -56,6 +56,9 @@
>   * suppressed them? */
>  #define VIRTIO_F_NOTIFY_ON_EMPTY	24
>  
> +/* Driver supports the VIRTIO_CONFIG_S_NEEDS_RESET command */
> +#define VIRTIO_F_CAN_RESET		25
> +
>  /* Can the device handle any descriptor layout? */
>  #define VIRTIO_F_ANY_LAYOUT		27
>  #endif /* VIRTIO_CONFIG_NO_LEGACY */
> -- 
> 2.14.1.342.g6490525c54-goog