mounts/org.osbuild.btrfs: add support for mounting subvolumes

Co-authored-by: Christian Kellner <christian@kellner.me>

mounts/org.osbuild.btrfs

@@ -37,6 +37,10 @@ SCHEMA_2 = """
         "description": "Don't load the journal on mounting",
         "type": "boolean",
         "default": false
+      },
+      "subvol": {
+        "description": "Subvolume to be mounted",
+        "type": "string"
       }
     }
   }

osbuild/mounts.py

@@ -139,6 +139,8 @@ class FileSystemMountService(MountService):
             opts.append(f"umask={options['umask']}")
         if "shortname" in options:
             opts.append(f"shortname={options['shortname']}")
+        if "subvol" in options:
+            opts.append(f"subvol={options['subvol']}")
         if opts:
             return ["-o", ",".join(opts)]
         return []