Clarification of VIRTIO_F_EVENT_IDX driver conditions.

[Patrick Mosca <pmosca@apple.com>]

We ran into an edge case in the VIRTIO_F_EVENT_IDX feature where a notification could be missed if there is a "streak" in skipped notifications. If the difference between the event index and available index wraps before a notification is needed, there exists a case where a notification must be sent but is not sent.


Signed-off-by: Patrick Mosca <pmosca@apple.com>
Signed-off-by: Cameron Esfahani <dirty@apple.com>
---
 split-ring.tex | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/split-ring.tex b/split-ring.tex
index bfef62d..9650e5e 100644
--- a/split-ring.tex
+++ b/split-ring.tex
@@ -530,6 +530,9 @@ \subsection{Available Buffer Notification Suppression}\label{sec:Basic Facilitie
         \item If the \field{idx} field in the available ring (which determined
           where that descriptor index was placed) was equal to
           \field{avail_event}, the driver MUST send a notification.
+        \item If the number of descriptors added to the queue since
+          the last notification is greater than 65535, the driver MUST
+          send a notification.
         \item Otherwise the driver SHOULD NOT send a notification.
   \end{itemize}
 \end{itemize}
-- 
2.32.0 (Apple Git-131)


-Patrick Mosca