block: Accept node-name for drive-mirror

In order to remove the necessity to use BlockBackend names in the
external API, we want to allow node-names everywhere. This converts
drive-mirror to accept a node-name without lifting the restriction that
we're operating at a root node.

In case of an invalid device name, the command returns the GenericError
error class now instead of DeviceNotFound, because this is what
qmp_get_root_bs() returns.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
diff --git a/blockdev.c b/blockdev.c
index 773336c..a392e08 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3429,7 +3429,6 @@
 void qmp_drive_mirror(DriveMirror *arg, Error **errp)
 {
     BlockDriverState *bs;
-    BlockBackend *blk;
     BlockDriverState *source, *target_bs;
     AioContext *aio_context;
     BlockMirrorBackingMode backing_mode;
@@ -3439,21 +3438,14 @@
     int64_t size;
     const char *format = arg->format;
 
-    blk = blk_by_name(arg->device);
-    if (!blk) {
-        error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
-                  "Device '%s' not found", arg->device);
+    bs = qmp_get_root_bs(arg->device, errp);
+    if (!bs) {
         return;
     }
 
-    aio_context = blk_get_aio_context(blk);
+    aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
-    if (!blk_is_available(blk)) {
-        error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, arg->device);
-        goto out;
-    }
-    bs = blk_bs(blk);
     if (!arg->has_mode) {
         arg->mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
     }