block: make 'top' argument to block-commit optional

Now that active layer block-commit is supported, the 'top' argument
no longer needs to be mandatory.

Change it to optional, with the default being the active layer in the
device chain.

[kwolf: Rebased and resolved conflict in tests/qemu-iotests/040]

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

blockdev.c

@@ -1913,7 +1913,8 @@ 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)
 {
@@ -1932,6 +1933,11 @@ void qmp_block_commit(const char *device,
     /* drain all i/o before commits */
     bdrv_drain_all();
 
+    /* Important Note:
+     *  libvirt relies on the DeviceNotFound error class in order to probe for
+     *  live commit feature versions; for this to work, we must make sure to
+     *  perform the device lookup before any generic errors that may occur in a
+     *  scenario in which all optional arguments are omitted. */
     bs = bdrv_find(device);
     if (!bs) {
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
@@ -1945,7 +1951,7 @@ 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);
         }
@@ -1967,6 +1973,12 @@ void qmp_block_commit(const char *device,
         return;
     }
 
+    /* Do not allow attempts to commit an image into itself */
+    if (top_bs == base_bs) {
+        error_setg(errp, "cannot commit an image into itself");
+        return;
+    }
+
     if (top_bs == bs) {
         commit_active_start(bs, base_bs, speed, on_error, block_job_cb,
                             bs, &local_err);

qapi/block-core.json

@@ -690,8 +690,9 @@
 # @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,
+# @top:    #optional 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.
 #
 #                    If top == base, that is an error.
 #                    If top == active, the job will not be completed by itself,
@@ -719,7 +720,7 @@
 #
 ##
 { 'command': 'block-commit',
-  'data': { 'device': 'str', '*base': 'str', 'top': 'str',
+  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
             '*speed': 'int' } }
 
 ##

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,

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, need_ready=False):
+    def wait_for_complete(self, need_ready=False):
-        self.assert_no_active_block_jobs()
-        result = self.vm.qmp('block-commit', device='drive0', top=top, base=base)
-        self.assert_qmp(result, 'return', {})
-
         completed = False
         ready = False
         while not completed:
@@ -62,6 +58,18 @@ class ImageCommitTestCase(iotests.QMPTestCase):
         self.assert_no_active_block_jobs()
         self.vm.shutdown()
 
+    def run_commit_test(self, top, base, need_ready=False):
+        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(need_ready)
+
+    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
@@ -113,17 +121,17 @@ 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