qapi: add '@fdset' feature for BlockdevOptionsVirtioBlkVhostVdpa

The virtio-blk-vhost-vdpa driver in libblkio 1.3.0 supports the fd
passing through the new 'fd' property.

Since now we are using qemu_open() on '@path' if the virtio-blk driver
supports the fd passing, let's announce it.
In this way, the management layer can pass the file descriptor of an
already opened vhost-vdpa character device. This is useful especially
when the device can only be accessed with certain privileges.

Add the '@fdset' feature only when the virtio-blk-vhost-vdpa driver
in libblkio supports it.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230530071941.8954-3-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

meson.build

@@ -2106,6 +2106,10 @@ config_host_data.set('CONFIG_LZO', lzo.found())
 config_host_data.set('CONFIG_MPATH', mpathpersist.found())
 config_host_data.set('CONFIG_MPATH_NEW_API', mpathpersist_new_api)
 config_host_data.set('CONFIG_BLKIO', blkio.found())
+if blkio.found()
+  config_host_data.set('CONFIG_BLKIO_VHOST_VDPA_FD',
+                       blkio.version().version_compare('>=1.3.0'))
+endif
 config_host_data.set('CONFIG_CURL', curl.found())
 config_host_data.set('CONFIG_CURSES', curses.found())
 config_host_data.set('CONFIG_GBM', gbm.found())

qapi/block-core.json

@@ -3955,10 +3955,16 @@
 #
 # @path: path to the vhost-vdpa character device.
 #
+# Features:
+# @fdset: Member @path supports the special "/dev/fdset/N" path
+#     (since 8.1)
+#
 # Since: 7.2
 ##
 { 'struct': 'BlockdevOptionsVirtioBlkVhostVdpa',
   'data': { 'path': 'str' },
+  'features': [ { 'name' :'fdset',
+                  'if': 'CONFIG_BLKIO_VHOST_VDPA_FD' } ],
   'if': 'CONFIG_BLKIO' }
 
 ##