Add option for QEMU Gluster libgfapi support

If gluster is present in qemu_allowed_storage_drivers, glusterfs's
backend will pass a disk configuration to QEMU. This allows QEMU to
access the volume using libgfapi rather than mounting GlusterFS via
fuse.

Implements blueprint glusterfs-native-support
DocImpact

Co-authored-by: Flavio Percoco <flavio@redhat.com>
Change-Id: I939cac05ee333b77abcaa9bd132d5eb3308e60ff

etc/nova/nova.conf.sample

@@ -2116,6 +2116,10 @@
 # Base dir where Scality SOFS shall be mounted (string value)
 #scality_sofs_mount_point=$state_path/scality
 
+# Protocols listed here will be accessed directly from QEMU.
+# Currently supported protocols: [gluster] (list value)
+#qemu_allowed_storage_drivers=
+
 
 #
 # Options defined in nova.virt.powervm.driver

nova/tests/virt/libvirt/test_libvirt_volume.py

@@ -471,6 +471,32 @@ class LibvirtVolumeTestCase(test.TestCase):
              export_string, export_mnt_base)]
         self.assertEqual(self.executes, expected_commands)
 
+    def test_libvirt_glusterfs_libgfapi(self):
+        self.flags(qemu_allowed_storage_drivers=['gluster'])
+        libvirt_driver = volume.LibvirtGlusterfsVolumeDriver(self.fake_conn)
+        export_string = '192.168.1.1:/volume-00001'
+        name = 'volume-00001'
+
+        connection_info = {'data': {'export': export_string, 'name': name}}
+
+        disk_info = {
+            "dev": "vde",
+            "type": "disk",
+            "bus": "virtio",
+        }
+
+        conf = libvirt_driver.connect_volume(connection_info, disk_info)
+        tree = conf.format_dom()
+        self.assertEqual(tree.get('type'), 'network')
+        self.assertEqual(tree.find('./driver').get('type'), 'raw')
+
+        source = tree.find('./source')
+        self.assertEqual(source.get('protocol'), 'gluster')
+        self.assertEqual(source.get('name'), 'volume-00001/volume-00001')
+        self.assertEqual(source.find('./host').get('name'), '192.168.1.1')
+
+        libvirt_driver.disconnect_volume(connection_info, "vde")
+
     def fibrechan_connection(self, volume, location, wwn):
         return {
                 'driver_volume_type': 'fibrechan',

nova/virt/libvirt/volume.py

@@ -73,6 +73,10 @@ volume_opts = [
     cfg.StrOpt('scality_sofs_mount_point',
                default='$state_path/scality',
                help='Base dir where Scality SOFS shall be mounted'),
+    cfg.ListOpt('qemu_allowed_storage_drivers',
+               default=[],
+               help='Protocols listed here will be accessed directly '
+                    'from QEMU. Currently supported protocols: [gluster]')
     ]
 
 CONF = cfg.CONF
@@ -604,11 +608,23 @@ class LibvirtGlusterfsVolumeDriver(LibvirtBaseVolumeDriver):
         """Connect the volume. Returns xml for libvirt."""
         conf = super(LibvirtGlusterfsVolumeDriver,
                      self).connect_volume(connection_info, mount_device)
-        options = connection_info['data'].get('options')
-        path = self._ensure_mounted(connection_info['data']['export'], options)
-        path = os.path.join(path, connection_info['data']['name'])
-        conf.source_type = 'file'
-        conf.source_path = path
+
+        data = connection_info['data']
+
+        if 'gluster' in CONF.qemu_allowed_storage_drivers:
+            vol_name = data['export'].split('/')[1]
+            source_host = data['export'].split('/')[0][:-1]
+
+            conf.source_ports = [None]
+            conf.source_type = 'network'
+            conf.source_protocol = 'gluster'
+            conf.source_hosts = [source_host]
+            conf.source_name = '%s/%s' % (vol_name, data['name'])
+        else:
+            path = self._ensure_mounted(data['export'], data.get('options'))
+            path = os.path.join(path, data['name'])
+            conf.source_type = 'file'
+            conf.source_path = path
         return conf
 
     def _ensure_mounted(self, glusterfs_export, options=None):