file-posix: Add 'locking' option

Making this option available even before implementing it will let
converting tests easier: in coming patches they can specify the option
already when necessary, before we actually write code to lock the
images.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -392,6 +392,11 @@ static QemuOptsList raw_runtime_opts = {
             .type = QEMU_OPT_STRING,
             .help = "host AIO implementation (threads, native)",
         },
+        {
+            .name = "locking",
+            .type = QEMU_OPT_STRING,
+            .help = "file locking mode (on/off/auto, default: auto)",
+        },
         { /* end of list */ }
     },
 };

qapi/block-core.json

@@ -2127,11 +2127,15 @@
 #
 # @filename:    path to the image file
 # @aio:         AIO backend (default: threads) (since: 2.8)
+# @locking:     whether to enable file locking. If set to 'auto', only enable
+#               when Open File Descriptor (OFD) locking API is available
+#               (default: auto, since 2.10)
 #
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsFile',
   'data': { 'filename': 'str',
+            '*locking': 'OnOffAuto',
             '*aio': 'BlockdevAioOptions' } }
 
 ##