block/qcow: Improve error when opening qcow2 files as qcow

Reported-by:  <radmehrsaeed7@gmail.com>
Fixes: https://bugs.launchpad.net/bugs/1832914


Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow.c

@@ -156,7 +156,12 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
     if (header.version != QCOW_VERSION) {
-        error_setg(errp, "Unsupported qcow version %" PRIu32, header.version);
+        error_setg(errp, "qcow (v%d) does not support qcow version %" PRIu32,
+                   QCOW_VERSION, header.version);
+        if (header.version == 2 || header.version == 3) {
+            error_append_hint(errp, "Try the 'qcow2' driver instead.\n");
+        }
+
         ret = -ENOTSUP;
         goto fail;
     }