[PATCH 9/9] vhost-vdpa: allow pre-opend file descriptor

[Jason Wang <jasowang@redhat.com>]

This patch allows to initialize vhost-vdpa network backend with pre
opened vhost-vdpa file descriptor. This is useful for running
unprivileged qemu through libvirt.

Cc: Eric Blake <eblake@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 net/vhost-vdpa.c | 24 +++++++++++++++++++-----
 qapi/net.json    |  5 ++++-
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 9a6f0b63d3..f6385cd264 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -206,20 +206,34 @@ int net_init_vhost_vdpa(const Netdev *netdev, const char *name,
                           (char *)name, errp)) {
         return -1;
     }
-    if (!opts->has_vhostdev) {
-        error_setg(errp, "vhost-vdpa requires vhostdev to be set");
+    if (!(opts->has_vhostdev ^ opts->has_fd)) {
+        error_setg(errp, "Vhost-vdpa requires either vhostdev or fd to be set");
         return -1;
     }
 
     assert(name);
 
     nc = qemu_new_net_client(&net_vhost_vdpa_info, peer, TYPE_VHOST_VDPA, name);
-    snprintf(nc->info_str, sizeof(nc->info_str), "vhostdev=%s", opts->vhostdev);
+    if (opts->has_vhostdev) {
+        snprintf(nc->info_str, sizeof(nc->info_str),
+                 "vhostdev=%s", opts->vhostdev);
+        vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR);
+        if (vdpa_device_fd == -1) {
+            error_setg(errp, "Fail to open vhost-vdpa device %s",
+                       opts->vhostdev);
+            return -errno;
+        }
+    } else {
+        snprintf(nc->info_str, sizeof(nc->info_str), "fd=%s", opts->fd);
+        vdpa_device_fd = monitor_fd_param(cur_mon, opts->fd, errp);
+        if (vdpa_device_fd == -1) {
+            return -1;
+        }
+    }
 
     s = DO_UPCAST(VhostVDPAState, nc, nc);
-    vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR);
     if (vdpa_device_fd == -1) {
-        error_setg(errp, "Fail to open vhost-vdpa device %s", opts->vhostdev);
+
         return -errno;
     }
     s->vhost_vdpa.device_fd = vdpa_device_fd;
diff --git a/qapi/net.json b/qapi/net.json
index a2a94fad3e..5ad60c3045 100644
--- a/qapi/net.json
+++ b/qapi/net.json
@@ -442,12 +442,15 @@
 # @queues: number of queues to be created for multiqueue vhost-vdpa
 #          (default: 1)
 #
+# @fd: file descriptor of an already opened vhost-vdpa (since 5.2)
+#
 # Since: 5.1
 ##
 { 'struct': 'NetdevVhostVDPAOptions',
   'data': {
     '*vhostdev':     'str',
-    '*queues':       'int' } }
+    '*queues':       'int',
+    '*fd':           'str' } }
 
 ##
 # @NetClientDriver:
-- 
2.20.1