lguest: clean up length-used value in example launcher
The "len" field in the used ring for virtio indicates the number of
bytes *written* to the buffer. This means the guest doesn't have to
zero the buffers in advance as it always knows the used length.
Erroneously, the console and network example code puts the length
*read* into that field. The guest ignores it, but it's wrong.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 9f3240c..8704600 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -830,15 +830,14 @@
static void handle_console_output(struct virtqueue *vq, bool timeout)
{
unsigned int head, out, in;
- int len;
struct iovec iov[vq->vring.num];
/* Keep getting output buffers from the Guest until we run out. */
while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
if (in)
errx(1, "Input buffers in output queue?");
- len = writev(STDOUT_FILENO, iov, out);
- add_used_and_trigger(vq, head, len);
+ writev(STDOUT_FILENO, iov, out);
+ add_used_and_trigger(vq, head, 0);
}
}
@@ -870,7 +869,6 @@
static void handle_net_output(struct virtqueue *vq, bool timeout)
{
unsigned int head, out, in, num = 0;
- int len;
struct iovec iov[vq->vring.num];
static int last_timeout_num;
@@ -878,10 +876,9 @@
while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
if (in)
errx(1, "Input buffers in output queue?");
- len = writev(vq->dev->fd, iov, out);
- if (len < 0)
+ if (writev(vq->dev->fd, iov, out) < 0)
err(1, "Writing network packet to tun");
- add_used_and_trigger(vq, head, len);
+ add_used_and_trigger(vq, head, 0);
num++;
}