[v4,04/10] block: make 'top' argument to block-commit optional

diff --git a/blockdev.c b/blockdev.c
index 9b5261b..58b526a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1914,7 +1914,8 @@  void qmp_block_stream(const char *device, bool has_base,
 }
 
 void qmp_block_commit(const char *device,
-                      bool has_base, const char *base, const char *top,
+                      bool has_base, const char *base,
+                      bool has_top, const char *top,
                       bool has_speed, int64_t speed,
                       Error **errp)
 {
@@ -1946,7 +1947,7 @@  void qmp_block_commit(const char *device,
     /* default top_bs is the active layer */
     top_bs = bs;
 
-    if (top) {
+    if (has_top && top) {
         if (strcmp(bs->filename, top) != 0) {
             top_bs = bdrv_find_backing_image(bs, top);
         }
diff --git a/qapi-schema.json b/qapi-schema.json
index 7bc33ea..97cf053 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2102,8 +2102,9 @@ 
 # @base:   #optional The file name of the backing image to write data into.
 #                    If not specified, this is the deepest backing image
 #
-# @top:              The file name of the backing image within the image chain,
-#                    which contains the topmost data to be committed down.
+# @top:    #optional The file name of the backing image within the image chain,
+#                    which contains the topmost data to be committed down. If
+#                    not specified, this is the active layer.
 #
 #                    If top == base, that is an error.
 #                    If top == active, the job will not be completed by itself,
@@ -2131,7 +2132,7 @@ 
 #
 ##
 { 'command': 'block-commit',
-  'data': { 'device': 'str', '*base': 'str', 'top': 'str',
+  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
             '*speed': 'int' } }
 
 ##
diff --git a/qmp-commands.hx b/qmp-commands.hx
index d8aa4ed..6b67d2f 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -985,7 +985,7 @@  EQMP
 
     {
         .name       = "block-commit",
-        .args_type  = "device:B,base:s?,top:s,speed:o?",
+        .args_type  = "device:B,base:s?,top:s?,speed:o?",
         .mhandler.cmd_new = qmp_marshal_input_block_commit,
     },
 
@@ -1003,7 +1003,8 @@  Arguments:
           If not specified, this is the deepest backing image
           (json-string, optional)
 - "top":  The file name of the backing image within the image chain,
-          which contains the topmost data to be committed down.
+          which contains the topmost data to be committed down. If
+          not specified, this is the active layer. (json-string, optional)
 
           If top == base, that is an error.
           If top == active, the job will not be completed by itself,
diff --git a/tests/qemu-iotests/040 b/tests/qemu-iotests/040
index 734b6a6..803b0c7 100755
--- a/tests/qemu-iotests/040
+++ b/tests/qemu-iotests/040
@@ -35,11 +35,7 @@  test_img = os.path.join(iotests.test_dir, 'test.img')
 class ImageCommitTestCase(iotests.QMPTestCase):
     '''Abstract base class for image commit test cases'''
 
-    def run_commit_test(self, top, base):
-        self.assert_no_active_block_jobs()
-        result = self.vm.qmp('block-commit', device='drive0', top=top, base=base)
-        self.assert_qmp(result, 'return', {})
-
+    def wait_for_complete(self):
         completed = False
         while not completed:
             for event in self.vm.get_qmp_events(wait=True):
@@ -58,6 +54,18 @@  class ImageCommitTestCase(iotests.QMPTestCase):
         self.assert_no_active_block_jobs()
         self.vm.shutdown()
 
+    def run_commit_test(self, top, base):
+        self.assert_no_active_block_jobs()
+        result = self.vm.qmp('block-commit', device='drive0', top=top, base=base)
+        self.assert_qmp(result, 'return', {})
+        self.wait_for_complete()
+
+    def run_default_commit_test(self):
+        self.assert_no_active_block_jobs()
+        result = self.vm.qmp('block-commit', device='drive0')
+        self.assert_qmp(result, 'return', {})
+        self.wait_for_complete()
+
 class TestSingleDrive(ImageCommitTestCase):
     image_len = 1 * 1024 * 1024
     test_len = 1 * 1024 * 256
@@ -109,17 +117,17 @@  class TestSingleDrive(ImageCommitTestCase):
         self.assertEqual(-1, qemu_io('-c', 'read -P 0xab 0 524288', backing_img).find("verification failed"))
         self.assertEqual(-1, qemu_io('-c', 'read -P 0xef 524288 524288', backing_img).find("verification failed"))
 
+    def test_top_is_default_active(self):
+        self.run_default_commit_test()
+        self.assertEqual(-1, qemu_io('-c', 'read -P 0xab 0 524288', backing_img).find("verification failed"))
+        self.assertEqual(-1, qemu_io('-c', 'read -P 0xef 524288 524288', backing_img).find("verification failed"))
+
     def test_top_and_base_reversed(self):
         self.assert_no_active_block_jobs()
         result = self.vm.qmp('block-commit', device='drive0', top='%s' % backing_img, base='%s' % mid_img)
         self.assert_qmp(result, 'error/class', 'GenericError')
         self.assert_qmp(result, 'error/desc', 'Base \'%s\' not found' % mid_img)
 
-    def test_top_omitted(self):
-        self.assert_no_active_block_jobs()
-        result = self.vm.qmp('block-commit', device='drive0')
-        self.assert_qmp(result, 'error/class', 'GenericError')
-        self.assert_qmp(result, 'error/desc', "Parameter 'top' is missing")
 
 class TestRelativePaths(ImageCommitTestCase):
     image_len = 1 * 1024 * 1024