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

[Jason Wang]

On 2020/8/31 下午7:16, Cindy Lu wrote:

On Mon, 31 Aug 2020 at 16:30, Jason Wang <jasow...@redhat.com> wrote:

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 <ebl...@redhat.com>
Cc: Markus Armbruster <arm...@redhat.com>
Signed-off-by: Jason Wang <jasow...@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

I think the latest  code supported this part.
you can pass a pre open file descriptor to it via the add-fd QMP
command to /dev/fdset/NNN, and then pass the string
"/dev/fdset/NNN" as vhostdev.  so we don't need a special fd parameter here.

Right, I forgot the fdset tricks.


Thanks

Thanks
Cindy