[PULL 23/24] vhost-user: add VHOST_USER_RESET_DEVICE to reset devices

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

From: Raphael Norwitz <raphael.norwitz@nutanix.com>

Add a VHOST_USER_RESET_DEVICE message which will reset the vhost user
backend. Disabling all rings, and resetting all internal state, ready
for the backend to be reinitialized.

A backend has to report it supports this features with the
VHOST_USER_PROTOCOL_F_RESET_DEVICE protocol feature bit. If it does
so, the new message is used instead of sending a RESET_OWNER which has
had inconsistent implementations.

Signed-off-by: David Vrabel <david.vrabel@nutanix.com>
Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <1572385083-5254-2-git-send-email-raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio/vhost-user.c      |  8 +++++++-
 docs/interop/vhost-user.rst | 15 +++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 02a9b25199..d27a10fcc6 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -58,6 +58,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD = 10,
     VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
     VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
+    VHOST_USER_PROTOCOL_F_RESET_DEVICE = 13,
     VHOST_USER_PROTOCOL_F_MAX
 };
 
@@ -98,6 +99,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_INFLIGHT_FD = 31,
     VHOST_USER_SET_INFLIGHT_FD = 32,
     VHOST_USER_GPU_SET_SOCKET = 33,
+    VHOST_USER_RESET_DEVICE = 34,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -890,10 +892,14 @@ static int vhost_user_set_owner(struct vhost_dev *dev)
 static int vhost_user_reset_device(struct vhost_dev *dev)
 {
     VhostUserMsg msg = {
-        .hdr.request = VHOST_USER_RESET_OWNER,
         .hdr.flags = VHOST_USER_VERSION,
     };
 
+    msg.hdr.request = virtio_has_feature(dev->protocol_features,
+                                         VHOST_USER_PROTOCOL_F_RESET_DEVICE)
+        ? VHOST_USER_RESET_DEVICE
+        : VHOST_USER_RESET_OWNER;
+
     if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
         return -1;
     }
diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 015ac08177..5f8b3a456b 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -785,6 +785,7 @@ Protocol features
   #define VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD  10
   #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER  11
   #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD 12
+  #define VHOST_USER_PROTOCOL_F_RESET_DEVICE   13
 
 Master message types
 --------------------
@@ -1190,6 +1191,20 @@ Master message types
   ancillary data. The GPU protocol is used to inform the master of
   rendering state and updates. See vhost-user-gpu.rst for details.
 
+``VHOST_USER_RESET_DEVICE``
+  :id: 34
+  :equivalent ioctl: N/A
+  :master payload: N/A
+  :slave payload: N/A
+
+  Ask the vhost user backend to disable all rings and reset all
+  internal device state to the initial state, ready to be
+  reinitialized. The backend retains ownership of the device
+  throughout the reset operation.
+
+  Only valid if the ``VHOST_USER_PROTOCOL_F_RESET_DEVICE`` protocol
+  feature is set by the backend.
+
 Slave message types
 -------------------
 
-- 
MST