[PATCH v5 5/7] vhost_user.rst: Add GET_SHMEM_CONFIG message

[Albert Esteve <aesteve@redhat.com>]

Add GET_SHMEM_CONFIG vhost-user frontend
message to the spec documentation.

Reviewed-by: Alyssa Ross <hi@alyssa.is>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 docs/interop/vhost-user.rst | 39 +++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index b623284819..223bfe7cd7 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -371,6 +371,20 @@ MMAP request
   - 0: Pages are mapped read-only
   - 1: Pages are mapped read-write
 
+VIRTIO Shared Memory Region configuration
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
++-------------+---------+------------+----+--------------+
+| num regions | padding | mem size 0 | .. | mem size 255 |
++-------------+---------+------------+----+--------------+
+
+:num regions: a 32-bit number of regions
+
+:padding: 32-bit
+
+:mem size: contains ``num regions`` 64-bit fields representing the size of each
+           VIRTIO Shared Memory Region
+
 C structure
 -----------
 
@@ -397,6 +411,7 @@ In QEMU the vhost-user message is implemented with the following struct:
           VhostUserShared object;
           VhostUserTransferDeviceState transfer_state;
           VhostUserMMap mmap;
+          VhostUserShMemConfig shmem;
       };
   } QEMU_PACKED VhostUserMsg;
 
@@ -1754,6 +1769,30 @@ Front-end message types
   Using this function requires prior negotiation of the
   ``VHOST_USER_PROTOCOL_F_DEVICE_STATE`` feature.
 
+``VHOST_USER_GET_SHMEM_CONFIG``
+  :id: 44
+  :equivalent ioctl: N/A
+  :request payload: N/A
+  :reply payload: ``struct VhostUserShMemConfig``
+
+  When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been
+  successfully negotiated, this message can be submitted by the front-end
+  to gather the VIRTIO Shared Memory Region configuration. The back-end will
+  respond with the number of VIRTIO Shared Memory Regions it requires, and
+  each shared memory region size in an array. The shared memory IDs are
+  represented by the array index. The information returned shall comply
+  with the following rules:
+
+  * The shared information will remain valid and unchanged for the entire
+    lifetime of the connection.
+
+  * The Shared Memory Region size must be a multiple of the page size
+    supported by mmap(2).
+
+  * The size may be 0 if the region is unused. This can happen when the
+    device does not support an optional feature but does support a feature
+    that uses a higher shmid.
+
 Back-end message types
 ----------------------
 
-- 
2.49.0