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authorRusty Russell <rusty@rustcorp.com.au>2008-08-26 00:19:27 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-08-26 00:19:28 +1000
commit1dc3e3bcbfe335843ec938bfdddb34d10f4dd278 (patch)
tree8666189f7a285c8e4c6512784dff39971fefa30c
parentbf2002967775cbb233876d51ff94e8daa7e77858 (diff)
lguest: update commentry
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--Documentation/lguest/lguest.c8
-rw-r--r--drivers/lguest/lguest_device.c8
2 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 655414821ed..7228369d101 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -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)
{
struct itimerval itm;
@@ -939,6 +942,11 @@ static void handle_net_output(int fd, struct virtqueue *vq, bool timeout)
if (!timeout && num)
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 (num < last_timeout_num)
timeout_usec += 10;
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 37344aaee22..a661bbdae3d 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -98,6 +98,10 @@ static u32 lg_get_features(struct virtio_device *vdev)
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)
{
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. */
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);
bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
for (i = 0; i < bits; i++) {