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authorRusty Russell <rusty@rustcorp.com.au>2008-02-04 23:49:59 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-02-04 23:50:00 +1100
commit426e3e0af5d2473e67d4256fc1340b7faebd1cc7 (patch)
tree29912e63889e45307f41ef08116ecd895b17e21c
parent3309daaad724dd08eb598bf9c12b7bb9daddd706 (diff)
virtio: clarify NO_NOTIFY flag usage
The other side (host) can set the NO_NOTIFY flag as an optimization, to say "no need to kick me when you add things". Make it clear that this is advisory only; especially that we should always notify when the ring is full. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--Documentation/lguest/lguest.c9
-rw-r--r--drivers/virtio/virtio_ring.c2
-rw-r--r--include/linux/virtio_ring.h8
3 files changed, 13 insertions, 6 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 4df1804169d..8ff2d8bc690 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -923,10 +923,10 @@ static void handle_output(int fd, unsigned long addr)
/* Check each virtqueue. */
for (i = devices.dev; i; i = i->next) {
for (vq = i->vq; vq; vq = vq->next) {
- if (vq->config.pfn == addr/getpagesize()
- && vq->handle_output) {
+ if (vq->config.pfn == addr/getpagesize()) {
verbose("Output to %s\n", vq->dev->name);
- vq->handle_output(fd, vq);
+ if (vq->handle_output)
+ vq->handle_output(fd, vq);
return;
}
}
@@ -1068,7 +1068,8 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
* virtqueue. */
vq->handle_output = handle_output;
- /* Set the "Don't Notify Me" flag if we don't have a handler */
+ /* As an optimization, set the advisory "Don't Notify Me" flag if we
+ * don't have a handler */
if (!handle_output)
vq->vring.used->flags = VRING_USED_F_NO_NOTIFY;
}
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 342bb0363fb..dbe1d35db32 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -87,6 +87,8 @@ static int vring_add_buf(struct virtqueue *_vq,
if (vq->num_free < out + in) {
pr_debug("Can't add buf len %i - avail = %i\n",
out + in, vq->num_free);
+ /* We notify *even if* VRING_USED_F_NO_NOTIFY is set here. */
+ vq->notify(&vq->vq);
END_USE(vq);
return -ENOSPC;
}
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index ea3be89a0e8..abe481ed990 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -15,9 +15,13 @@
/* This marks a buffer as write-only (otherwise read-only). */
#define VRING_DESC_F_WRITE 2
-/* This means don't notify other side when buffer added. */
+/* The Host uses this in used->flags to advise the Guest: don't kick me when
+ * you add a buffer. It's unreliable, so it's simply an optimization. Guest
+ * will still kick if it's out of buffers. */
#define VRING_USED_F_NO_NOTIFY 1
-/* This means don't interrupt guest when buffer consumed. */
+/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
+ * when you consume a buffer. It's unreliable, so it's simply an
+ * optimization. */
#define VRING_AVAIL_F_NO_INTERRUPT 1
/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */