virtio: console makes incorrect assumption about virtio API

The get_buf() API sets the second arg to the number of bytes *written*
by the other side; in this case it should be zero as these are output buffers.

lguest gets this right (obviously kvm's console doesn't), resulting in
continual buildup of console writes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Amit Shah <amit.shah@redhat.com>

1 files changed, 3 insertions, 7 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 48306bc733f7..86e9011325dc 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -416,20 +416,16 @@ static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count)
         out_vq->vq_ops->kick(out_vq);
 
         if (ret < 0) {
-                len = 0;
+                in_count = 0;
                 goto fail;
         }
 
-        /*
-         * Wait till the host acknowledges it pushed out the data we
-         * sent. Also ensure we return to userspace the number of
-         * bytes that were successfully consumed by the host.
-         */
+        /* Wait till the host acknowledges it pushed out the data we sent. */
         while (!out_vq->vq_ops->get_buf(out_vq, &len))
                 cpu_relax();
 fail:
         /* We're expected to return the amount of data we wrote */
-        return len;
+        return in_count;
 }
 
 /*