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| author |   Rusty Russell <rusty@rustcorp.com.au> | 2008-02-04 23:49:59 -0500 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2008-02-04 23:50:00 +1100 |
| commit | 426e3e0af5d2473e67d4256fc1340b7faebd1cc7 (patch) | |
| tree | 29912e63889e45307f41ef08116ecd895b17e21c | |
| parent | virtio: Fix vring_init/vring_size to take unsigned long (diff) | |
| download | linux-dev-426e3e0af5d2473e67d4256fc1340b7faebd1cc7.tar.xz linux-dev-426e3e0af5d2473e67d4256fc1340b7faebd1cc7.zip | |
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.c | 9 | ||||
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 2 | ||||
| -rw-r--r-- | 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 4df1804169dc..8ff2d8bc690a 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 342bb0363fbe..dbe1d35db32a 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 ea3be89a0e83..abe481ed990e 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". */ |