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

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Message-Id: <1260902573.4387.76.camel@localhost.localdomain>
Date:	Tue, 15 Dec 2009 10:42:53 -0800
From:	Shirley Ma <mashirle@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: [RFC PATCH] Subject: virtio: Add unused buffers detach from vring

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@...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

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