virtio: make add_buf return capacity remaining

This API change means that virtio_net can tell how much capacity
remains for buffers.  It's necessarily fuzzy, since
VIRTIO_RING_F_INDIRECT_DESC means we can fit any number of descriptors
in one, *if* we can kmalloc.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Dinesh Subhraveti <dineshs@us.ibm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 4fca4f5440ba..057a2e010758 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -34,7 +34,7 @@ struct virtqueue {
  *      out_num: the number of sg readable by other side
  *      in_num: the number of sg which are writable (after readable ones)
  *      data: the token identifying the buffer.
- *      Returns 0 or an error.
+ *      Returns remaining capacity of queue (sg segments) or a negative error.
  * @kick: update after add_buf
  *      vq: the struct virtqueue
  *      After one or more add_buf calls, invoke this to kick the other side.