block: Fix blockdev-backup not to use funky error class

Error classes are a leftover from the days of "rich" error objects.
New code should always use ERROR_CLASS_GENERIC_ERROR.  Commit
b7b9d39a..7c6a4ab8 added uses of ERROR_CLASS_DEVICE_NOT_FOUND.  Replace
them.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -1574,14 +1574,14 @@ static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
 
     blk = blk_by_name(backup->device);
     if (!blk) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, backup->device);
+        error_setg(errp, "Device '%s' not found", backup->device);
         return;
     }
     bs = blk_bs(blk);
 
     blk = blk_by_name(backup->target);
     if (!blk) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, backup->target);
+        error_setg(errp, "Device '%s' not found", backup->target);
         return;
     }
     target = blk_bs(blk);
@@ -2421,7 +2421,7 @@ void qmp_blockdev_backup(const char *device, const char *target,
 
     blk = blk_by_name(device);
     if (!blk) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        error_setg(errp, "Device '%s' not found", device);
         return;
     }
     bs = blk_bs(blk);
@@ -2431,7 +2431,7 @@ void qmp_blockdev_backup(const char *device, const char *target,
 
     blk = blk_by_name(target);
     if (!blk) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, target);
+        error_setg(errp, "Device '%s' not found", target);
         goto out;
     }
     target_bs = blk_bs(blk);

qapi/block-core.json

@@ -882,9 +882,6 @@
 #
 # For the arguments, see the documentation of BlockdevBackup.
 #
-# Returns: Nothing on success.
-#          If @device or @target is not a valid block device, DeviceNotFound.
-#
 # Since 2.3
 ##
 { 'command': 'blockdev-backup', 'data': 'BlockdevBackup' }

tests/qemu-iotests/055

@@ -126,7 +126,10 @@ class TestSingleDrive(iotests.QMPTestCase):
 
     def do_test_device_not_found(self, cmd, **args):
         result = self.vm.qmp(cmd, **args)
+        if cmd == 'drive-backup':
             self.assert_qmp(result, 'error/class', 'DeviceNotFound')
+        else:
+            self.assert_qmp(result, 'error/class', 'GenericError')
 
     def test_device_not_found(self):
         self.do_test_device_not_found('drive-backup', device='nonexistent',
@@ -364,7 +367,7 @@ class TestSingleTransaction(iotests.QMPTestCase):
                           'sync': 'full' },
             }
         ])
-        self.assert_qmp(result, 'error/class', 'DeviceNotFound')
+        self.assert_qmp(result, 'error/class', 'GenericError')
 
         result = self.vm.qmp('transaction', actions=[{
                 'type': 'blockdev-backup',
@@ -373,7 +376,7 @@ class TestSingleTransaction(iotests.QMPTestCase):
                           'sync': 'full' },
             }
         ])
-        self.assert_qmp(result, 'error/class', 'DeviceNotFound')
+        self.assert_qmp(result, 'error/class', 'GenericError')
 
         result = self.vm.qmp('transaction', actions=[{
                 'type': 'blockdev-backup',
@@ -382,7 +385,7 @@ class TestSingleTransaction(iotests.QMPTestCase):
                           'sync': 'full' },
             }
         ])
-        self.assert_qmp(result, 'error/class', 'DeviceNotFound')
+        self.assert_qmp(result, 'error/class', 'GenericError')
 
     def test_target_is_source(self):
         result = self.vm.qmp('transaction', actions=[{