[PATCH] virtio: document ENOSPC

["Michael S. Tsirkin" <mst@redhat.com>]

drivers handle ENOSPC specially since it's an error one can
get from a working VQ. Document the semantics.

Reported-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio_ring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b784aab66867..97ab0cce527d 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2296,6 +2296,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
  * at the same time (except where noted).
  *
  * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
+ *
+ * NB: ENOSPC is a special code that is only returned on an attempt to add a
+ * buffer to a full VQ. It indicates that some buffers are outstanding and that
+ * the operation can be retried after some buffers have been used.
  */
 int virtqueue_add_sgs(struct virtqueue *_vq,
 		      struct scatterlist *sgs[],
-- 
MST