Christian Borntraeger wrote:
Am Mittwoch, 12. Dezember 2007 schrieb Rusty Russell:
> On Wednesday 12 December 2007 00:16:12 Christian Borntraeger wrote:
> > That would also work. We already have VRING_AVAIL_F_NO_INTERRUPT in
> > virtio_ring.c - maybe we can use that. Its hidden in callback and
> > restart handling, what about adding an explicit startup?
>
> Yes, I debated whether to make this a separate hook or not; the current
> method reduces the number of function calls without having two ways of
> disabling callbacks.
>
> In this case, simply starting devices with callbacks disabled and
> renaming 'restart' to 'enable' (or something) and calling it at the
> beginning is probably sufficient?
So you suggest something like the following patch? It seems to work but
there is still a theoretical race at startup. Therefore, I tend to agree
with Dor that a separate hook seems prefereable, so I am not fully sure if
the patch is the final solution:
I think the change below handles the race. Otherwise please detail the
use case.
ps: Its ok to answer that after your vacation.
---
drivers/block/virtio_blk.c | 3 ++-
drivers/net/virtio_net.c | 5 ++++-
drivers/virtio/virtio_ring.c | 9 ++++-----
include/linux/virtio.h | 4 ++--
4 files changed, 12 insertions(+), 9 deletions(-)
Index: kvm/drivers/virtio/virtio_ring.c
===================================================================
--- kvm.orig/drivers/virtio/virtio_ring.c
+++ kvm/drivers/virtio/virtio_ring.c
@@ -220,7 +220,7 @@ static void *vring_get_buf(struct virtqu
return ret;
}
-static bool vring_restart(struct virtqueue *_vq)
+static bool vring_enable(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -264,7 +264,7 @@ static struct virtqueue_ops vring_vq_ops
.add_buf = vring_add_buf,
.get_buf = vring_get_buf,
.kick = vring_kick,
- .restart = vring_restart,
+ .enable = vring_enable,
.shutdown = vring_shutdown,
};
@@ -299,9 +299,8 @@ struct virtqueue *vring_new_virtqueue(un
vq->in_use = false;
#endif
- /* No callback? Tell other side not to bother us. */
- if (!callback)
- vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
+ /* disable interrupts until we enable them */
+ vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
/* Put everything in free lists. */
vq->num_free = num;
Index: kvm/include/linux/virtio.h
===================================================================
--- kvm.orig/include/linux/virtio.h
+++ kvm/include/linux/virtio.h
@@ -41,7 +41,7 @@ struct virtqueue
* vq: the struct virtqueue we're talking about.
* len: the length written into the buffer
* Returns NULL or the "data" token handed to add_buf.
- * @restart: restart callbacks after callback returned false.
+ * @enable: restart callbacks after callback returned false.
* vq: the struct virtqueue we're talking about.
* This returns "false" (and doesn't re-enable) if there are pending
* buffers in the queue, to avoid a race.
@@ -65,7 +65,7 @@ struct virtqueue_ops {
void *(*get_buf)(struct virtqueue *vq, unsigned int *len);
- bool (*restart)(struct virtqueue *vq);
+ bool (*enable)(struct virtqueue *vq);
void (*shutdown)(struct virtqueue *vq);
};
Index: kvm/drivers/net/virtio_net.c
===================================================================
--- kvm.orig/drivers/net/virtio_net.c
+++ kvm/drivers/net/virtio_net.c
@@ -201,7 +201,7 @@ again:
/* Out of packets? */
if (received < budget) {
netif_rx_complete(vi->dev, napi);
- if (unlikely(!vi->rvq->vq_ops->restart(vi->rvq))
+ if (unlikely(!vi->rvq->vq_ops->enable(vi->rvq))
&& netif_rx_reschedule(vi->dev, napi))
goto again;
}
@@ -292,6 +292,9 @@ static int virtnet_open(struct net_devic
return -ENOMEM;
napi_enable(&vi->napi);
+
+ vi->rvq->vq_ops->enable(vi->rvq);
+ vi->svq->vq_ops->enable(vi->svq);
If you change it to:
if (!vi->rvq->vq_ops->enable(vi->rvq))
vi->rvq->vq_ops->kick(vi->rvq);
if (!vi->rvq->vq_ops->enable(vi->svq))
vi->rvq->vq_ops->kick(vi->svq);
You solve the race of packets already waiting in the queue without
triggering the irq.
The same for the block device.
Regards,
Dor.
return 0;
}
Index: kvm/drivers/block/virtio_blk.c
===================================================================
--- kvm.orig/drivers/block/virtio_blk.c
+++ kvm/drivers/block/virtio_blk.c
@@ -183,7 +183,8 @@ static int virtblk_probe(struct virtio_d
err = PTR_ERR(vblk->vq);
goto out_free_vblk;
}
-
+ /* enable interrupts */
+ vblk->vq->vq_ops->enable(vblk->vq);
vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct
virtblk_req));
if (!vblk->pool) {
err = -ENOMEM;
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