vhost-vdpa: allow passing opened vhostfd to vhost-vdpa

Similar to other vhost backends, vhostfd can be passed to vhost-vdpa
backend as another parameter to instantiate vhost-vdpa net client.
This would benefit the use case where only open file descriptors, as
opposed to raw vhost-vdpa device paths, are accessible from the QEMU
process.

(qemu) netdev_add type=vhost-vdpa,vhostfd=61,id=vhost-vdpa1

Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/vhost-vdpa.c

@@ -634,14 +634,29 @@ int net_init_vhost_vdpa(const Netdev *netdev, const char *name,
 
     assert(netdev->type == NET_CLIENT_DRIVER_VHOST_VDPA);
     opts = &netdev->u.vhost_vdpa;
-    if (!opts->vhostdev) {
+    if (!opts->has_vhostdev && !opts->has_vhostfd) {
-        error_setg(errp, "vdpa character device not specified with vhostdev");
+        error_setg(errp,
+                   "vhost-vdpa: neither vhostdev= nor vhostfd= was specified");
         return -1;
     }
 
-    vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR, errp);
+    if (opts->has_vhostdev && opts->has_vhostfd) {
-    if (vdpa_device_fd == -1) {
+        error_setg(errp,
-        return -errno;
+                   "vhost-vdpa: vhostdev= and vhostfd= are mutually exclusive");
+        return -1;
+    }
+
+    if (opts->has_vhostdev) {
+        vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR, errp);
+        if (vdpa_device_fd == -1) {
+            return -errno;
+        }
+    } else if (opts->has_vhostfd) {
+        vdpa_device_fd = monitor_fd_param(monitor_cur(), opts->vhostfd, errp);
+        if (vdpa_device_fd == -1) {
+            error_prepend(errp, "vhost-vdpa: unable to parse vhostfd: ");
+            return -1;
+        }
     }
 
     r = vhost_vdpa_get_features(vdpa_device_fd, &features, errp);

qapi/net.json

@@ -442,6 +442,8 @@
 # @vhostdev: path of vhost-vdpa device
 #            (default:'/dev/vhost-vdpa-0')
 #
+# @vhostfd: file descriptor of an already opened vhost vdpa device
+#
 # @queues: number of queues to be created for multiqueue vhost-vdpa
 #          (default: 1)
 #
@@ -456,6 +458,7 @@
 { 'struct': 'NetdevVhostVDPAOptions',
   'data': {
     '*vhostdev':     'str',
+    '*vhostfd':      'str',
     '*queues':       'int',
     '*x-svq':        {'type': 'bool', 'features' : [ 'unstable'] } } }
 

qemu-options.hx

@@ -2790,8 +2790,10 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
     "                configure a vhost-user network, backed by a chardev 'dev'\n"
 #endif
 #ifdef __linux__
-    "-netdev vhost-vdpa,id=str,vhostdev=/path/to/dev\n"
+    "-netdev vhost-vdpa,id=str[,vhostdev=/path/to/dev][,vhostfd=h]\n"
     "                configure a vhost-vdpa network,Establish a vhost-vdpa netdev\n"
+    "                use 'vhostdev=/path/to/dev' to open a vhost vdpa device\n"
+    "                use 'vhostfd=h' to connect to an already opened vhost vdpa device\n"
 #endif
 #ifdef CONFIG_VMNET
     "-netdev vmnet-host,id=str[,isolated=on|off][,net-uuid=uuid]\n"
@@ -3296,7 +3298,7 @@ SRST
              -netdev type=vhost-user,id=net0,chardev=chr0 \
              -device virtio-net-pci,netdev=net0
 
-``-netdev vhost-vdpa,vhostdev=/path/to/dev``
+``-netdev vhost-vdpa[,vhostdev=/path/to/dev][,vhostfd=h]``
     Establish a vhost-vdpa netdev.
 
     vDPA device is a device that uses a datapath which complies with