Re: [RFC PATCH] Subject: virtio: Add unused buffers detach from vring

Michael S. Tsirkin
2009-12-15T18:50:27Z

On Tue, Dec 15, 2009 at 10:42:53AM -0800, Shirley Ma wrote:
> I submit one split patch for review to make sure that's the right format.
> I copied Rusty's comment for the commit message, and change destroy
> to detach since we destroy the buffers in caller. This patch is built
> against Dave's net-next tree.

Almost :) text not intended for git commit logs like the above
should go after ---, this way git am knows to skip it.

> There's currently no way for a virtio driver to ask for unused
> buffers, so it has to keep a list itself to reclaim them at shutdown.
> This is redundant, since virtio_ring stores that information. So
> add a new hook to do this: virtio_net will be the first user.
>
> Signed-off-by: Shirley Ma <xma@us.ibm.com>
> ---
> drivers/virtio/virtio_ring.c | 24 ++++++++++++++++++++++++
> include/linux/virtio.h | 1 +
> 2 files changed, 25 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index fbd2ecd..f847bc3 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -334,6 +334,29 @@ static bool vring_enable_cb(struct virtqueue *_vq)
> return true;
> }
>
> +/* This function is used to return vring unused buffers to caller for free */
> +static void *vring_detach_bufs(struct virtqueue *_vq)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> + unsigned int i;
> +
> + START_USE(vq);
> +
> + for (i = 0; i < vq->vring.num; ++i) {

This is a single statement loop, so you do not need {}
around it. Or even better:
for (i = 0; i < vq->vring.num; ++i) {
if (!vq->data[i])
continue;
...
}
which has less nesting.

> + if (vq->data[i]) {
> + /* detach_buf clears data, so grab it now. */

You wrote that comment, but did you read it :)

> + detach_buf(vq, i);
> + END_USE(vq);
> + return vq->data[i];

In fact, this will return NULL always, won't it?

> + }
> + }
> + /* That should have freed everything. */
> + BUG_ON(vq->num_free != vq->vring.num);
> +
> + END_USE(vq);
> + return NULL;
> +}
> +
> irqreturn_t vring_interrupt(int irq, void *_vq)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> @@ -360,6 +383,7 @@ static struct virtqueue_ops vring_vq_ops = {
> .kick = vring_kick,
> .disable_cb = vring_disable_cb,
> .enable_cb = vring_enable_cb,
> + .detach_bufs = vring_detach_bufs,
> };
>
> struct virtqueue *vring_new_virtqueue(unsigned int num,
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 057a2e0..d7da456 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -71,6 +71,7 @@ struct virtqueue_ops {
>
> void (*disable_cb)(struct virtqueue *vq);
> bool (*enable_cb)(struct virtqueue *vq);
> + void *(*detach_bufs)(struct virtqueue *vq);
> };

Please add documentation in virtio.h
Thanks!

>
> /**
>
> Thanks
> Shirley