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

Shirley Ma
2009-12-15T18:42:58Z

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.

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

/**

Thanks
Shirley