vhost-user: Change one_time to per_device request

Some devices, like virtio-scsi, consist of one vhost_dev, while others, like
virtio-net, contain multiple vhost_devs. The QEMU vhost-user code has a
concept of one-time messages which is misleading. One-time messages are sent
once per operation on the device, not once for the lifetime of the device.
Therefore, as discussed in [1], vhost_user_one_time_request should be
renamed to vhost_user_per_device_request and the relevant comments updated
to match the real functionality.

[1] https://lore.kernel.org/qemu-devel/20230127083027-mutt-send-email-mst@kernel.org/

Signed-off-by: Tom Lonergan <tom.lonergan@nutanix.com>
Message-Id: <20230628163927.108171-2-tom.lonergan@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

hw/virtio/vhost-user.c

@@ -367,7 +367,7 @@ static int process_message_reply(struct vhost_dev *dev,
     return msg_reply.payload.u64 ? -EIO : 0;
 }
 
-static bool vhost_user_one_time_request(VhostUserRequest request)
+static bool vhost_user_per_device_request(VhostUserRequest request)
 {
     switch (request) {
     case VHOST_USER_SET_OWNER:
@@ -392,11 +392,17 @@ static int vhost_user_write(struct vhost_dev *dev, VhostUserMsg *msg,
     int ret, size = VHOST_USER_HDR_SIZE + msg->hdr.size;
 
     /*
-     * For non-vring specific requests, like VHOST_USER_SET_MEM_TABLE,
-     * we just need send it once in the first time. For later such
-     * request, we just ignore it.
+     * Some devices, like virtio-scsi, are implemented as a single vhost_dev,
+     * while others, like virtio-net, contain multiple vhost_devs. For
+     * operations such as configuring device memory mappings or issuing device
+     * resets, which affect the whole device instead of individual VQs,
+     * vhost-user messages should only be sent once.
+     * 
+     * Devices with multiple vhost_devs are given an associated dev->vq_index
+     * so per_device requests are only sent if vq_index is 0.
      */
-    if (vhost_user_one_time_request(msg->hdr.request) && dev->vq_index != 0) {
+    if (vhost_user_per_device_request(msg->hdr.request)
+        && dev->vq_index != 0) {
         msg->hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK;
         return 0;
     }
@@ -1256,7 +1262,7 @@ static int vhost_user_get_u64(struct vhost_dev *dev, int request, uint64_t *u64)
         .hdr.flags = VHOST_USER_VERSION,
     };
 
-    if (vhost_user_one_time_request(request) && dev->vq_index != 0) {
+    if (vhost_user_per_device_request(request) && dev->vq_index != 0) {
         return 0;
     }