[1/2] virtio: Add detach unused buffer from vring

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 |   25 +++++++++++++++++++++++++
 include/linux/virtio.h       |    4 ++++
 2 files changed, 29 insertions(+), 0 deletions(-)



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On Thu, Dec 17, 2009 at 11:43:50PM -0800, Shirley Ma wrote:
> 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>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> --- 
>  drivers/virtio/virtio_ring.c |   25 +++++++++++++++++++++++++
>  include/linux/virtio.h       |    4 ++++
>  2 files changed, 29 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index fbd2ecd..71929ee 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -334,6 +334,30 @@ static bool vring_enable_cb(struct virtqueue *_vq)
>  	return true;
>  }
>  
> +static void *vring_detach_unused_buf(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring.num; i++) {
> +		if (!vq->data[i])
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->data[i];
> +		detach_buf(vq, i);
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* 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 +384,7 @@ static struct virtqueue_ops vring_vq_ops = {
>  	.kick = vring_kick,
>  	.disable_cb = vring_disable_cb,
>  	.enable_cb = vring_enable_cb,
> +	.detach_unused_buf = vring_detach_unused_buf,
>  };
>  
>  struct virtqueue *vring_new_virtqueue(unsigned int num,
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 057a2e0..f508c65 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -51,6 +51,9 @@ struct virtqueue {
>   *	This re-enables callbacks; it returns "false" if there are pending
>   *	buffers in the queue, to detect a possible race between the driver
>   *	checking for more work, and enabling callbacks.
> + * @detach_unused_buf: detach first unused buffer
> + * 	vq: the struct virtqueue we're talking about.
> + * 	Returns NULL or the "data" token handed to add_buf
>   *
>   * Locking rules are straightforward: the driver is responsible for
>   * locking.  No two operations may be invoked simultaneously, with the exception
> @@ -71,6 +74,7 @@ struct virtqueue_ops {
>  
>  	void (*disable_cb)(struct virtqueue *vq);
>  	bool (*enable_cb)(struct virtqueue *vq);
> +	void *(*detach_unused_buf)(struct virtqueue *vq);
>  };
>  
>  /**
> 
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On (Thu) Dec 17 2009 [23:43:50], Shirley Ma wrote:
> 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>

Acked-By: Amit Shah <amit.shah@redhat.com>

		Amit
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