Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=426e3e0af5d2473e67d4256fc1340b7faebd1cc7
Commit: 426e3e0af5d2473e67d4256fc1340b7faebd1cc7
Parent: 3309daaad724dd08eb598bf9c12b7bb9daddd706
Author: Rusty Russell <[EMAIL PROTECTED]>
AuthorDate: Mon Feb 4 23:49:59 2008 -0500
Committer: Rusty Russell <[EMAIL PROTECTED]>
CommitDate: Mon Feb 4 23:50:00 2008 +1100
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 <[EMAIL PROTECTED]>
---
Documentation/lguest/lguest.c | 9 +++++----
drivers/virtio/virtio_ring.c | 2 ++
include/linux/virtio_ring.h | 8 ++++++--
3 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 4df1804..8ff2d8b 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 342bb03..dbe1d35 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 ea3be89..abe481e 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". */
-
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