linux-kernel - Re: [PATCH 1/6] virtio_balloon: transitional interface

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Message-ID: <20150330195508-mutt-send-email-mst@redhat.com>
Date:	Mon, 30 Mar 2015 19:55:53 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH 1/6] virtio_balloon: transitional interface

On Mon, Mar 30, 2015 at 07:37:12PM +0200, Michael S. Tsirkin wrote:
> Virtio 1.0 doesn't include a modern balloon device.
> But it's not a big change to support a transitional
> balloon device: this has the advantage of supporting
> existing drivers, transparently.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---

Hmm, re-reading the code, this won't be enough for BE
guests. We are doing one extra byteswap there.

I'll fix up and repost.

>  include/uapi/linux/virtio_balloon.h | 6 ++++++
>  drivers/virtio/virtio_balloon.c     | 8 ++++++--
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 4b0488f..5d83902 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -56,4 +56,10 @@ struct virtio_balloon_stat {
>  	__u64 val;
>  } __attribute__((packed));
>  
> +struct virtio_balloon_stat_modern {
> +	__u8 reserved[6];
> +	__u16 tag;
> +	__u64 val;
> +};
> +
>  #endif /* _LINUX_VIRTIO_BALLOON_H */
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 6a356e3..68e937f 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -77,7 +77,7 @@ struct virtio_balloon {
>  
>  	/* Memory statistics */
>  	int need_stats_update;
> -	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
> +	struct virtio_balloon_stat_modern stats[VIRTIO_BALLOON_S_NR];
>  
>  	/* To register callback in oom notifier call chain */
>  	struct notifier_block nb;
> @@ -269,7 +269,11 @@ static void stats_handle_request(struct virtio_balloon *vb)
>  	vq = vb->stats_vq;
>  	if (!virtqueue_get_buf(vq, &len))
>  		return;
> -	sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> +	if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
> +		sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> +	else
> +		sg_init_one(&sg, &vb->stats->tag, sizeof(vb->stats) -
> +			    offsetof(typeof(*vb->stats, tag);
>  	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
>  	virtqueue_kick(vq);
>  }
> -- 
> MST
> 
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