docs: Update vhost-user spec regarding backend program conventions

[Boeuf, Sebastien]

From c073d528b8cd7082832fd1825dc33dd65b305aa2 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <address@hidden>
Date: Tue, 11 Feb 2020 16:01:22 +0100
Subject: [PATCH] docs: Update vhost-user spec regarding backend program
 conventions

The vhost-user specification is not clearly stating the expected
behavior from a backend program whenever the client disconnects.

This patch addresses the issue by defining the default behavior and
proposing an alternative through a command line option.

By default, a backend program will have to keep listening even if the
client disconnects, unless told otherwise through the newly introduced
option --exit-on-disconnect.

Signed-off-by: Sebastien Boeuf <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 docs/interop/vhost-user.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 5f8b3a456b..da9a1ebc4c 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -1323,6 +1323,10 @@ The backend program must end (as quickly and cleanly as 
possible) when
 the SIGTERM signal is received. Eventually, it may receive SIGKILL by
 the management layer after a few seconds.
 
+By default, the backend program continues running after the client
+disconnects. It accepts only 1 connection at a time on each UNIX domain
+socket.
+
 The following command line options have an expected behaviour. They
 are mandatory, unless explicitly said differently:
 
@@ -1337,6 +1341,12 @@ are mandatory, unless explicitly said differently:
   vhost-user socket as file descriptor FDNUM. It is incompatible with
   --socket-path.
 
+--exit-on-disconnect
+
+  When this option is provided, the backend program must terminate when
+  the client disconnects. This can be used to keep the backend program's
+  lifetime synchronized with its client process.
+
 --print-capabilities
 
   Output to stdout the backend capabilities in JSON format, and then
-- 
2.20.1

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