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lguest: update commentry

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Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2008-08-26 00:19:27 -05:00
parent bf20029677
commit 1dc3e3bcbf
2 changed files with 16 additions and 0 deletions
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8
Documentation/lguest/lguest.c
View file

@ -895,6 +895,9 @@ static void handle_console_output(int fd, struct virtqueue *vq, bool timeout)
} }
} }
/* This is called when we no longer want to hear about Guest changes to a
* virtqueue. This is more efficient in high-traffic cases, but it means we
* have to set a timer to check if any more changes have occurred. */
static void block_vq(struct virtqueue *vq) static void block_vq(struct virtqueue *vq)
{ {
struct itimerval itm; struct itimerval itm;
@ -939,6 +942,11 @@ static void handle_net_output(int fd, struct virtqueue *vq, bool timeout)
if (!timeout && num) if (!timeout && num)
block_vq(vq); block_vq(vq);
/* We never quite know how long should we wait before we check the
* queue again for more packets. We start at 500 microseconds, and if
* we get fewer packets than last time, we assume we made the timeout
* too small and increase it by 10 microseconds. Otherwise, we drop it
* by one microsecond every time. It seems to work well enough. */
if (timeout) { if (timeout) {
if (num < last_timeout_num) if (num < last_timeout_num)
timeout_usec += 10; timeout_usec += 10;

8
drivers/lguest/lguest_device.c
View file

@ -98,6 +98,10 @@ static u32 lg_get_features(struct virtio_device *vdev)
return features; return features;
} }
/* The virtio core takes the features the Host offers, and copies the
* ones supported by the driver into the vdev->features array. Once
* that's all sorted out, this routine is called so we can tell the
* Host which features we understand and accept. */
static void lg_finalize_features(struct virtio_device *vdev) static void lg_finalize_features(struct virtio_device *vdev)
{ {
unsigned int i, bits; unsigned int i, bits;
@ -108,6 +112,10 @@ static void lg_finalize_features(struct virtio_device *vdev)
/* Give virtio_ring a chance to accept features. */ /* Give virtio_ring a chance to accept features. */
vring_transport_features(vdev); vring_transport_features(vdev);
/* The vdev->feature array is a Linux bitmask: this isn't the
* same as a the simple array of bits used by lguest devices
* for features. So we do this slow, manual conversion which is
* completely general. */
memset(out_features, 0, desc->feature_len); memset(out_features, 0, desc->feature_len);
bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8; bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
for (i = 0; i < bits; i++) { for (i = 0; i < bits; i++) {