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virtio: clarify NO_NOTIFY flag usage

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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>
This commit is contained in:
Rusty Russell 2008-02-04 23:49:59 -05:00
parent 3309daaad7
commit 426e3e0af5
3 changed files with 13 additions and 6 deletions
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9
Documentation/lguest/lguest.c
View File

@ -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;
}

2
drivers/virtio/virtio_ring.c
View File

@ -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;
}

8
include/linux/virtio_ring.h
View File

@ -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". */