block: Open by reference will try device then node_name.

Since we introduced node_name for named bs of the graph modify the opening by
reference to use it as a fallback.

This patch also enforce the separation of the device id and graph node
namespaces.
Signed-off-by: NBenoit Canet <benoit@irqsave.net>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -796,6 +796,13 @@ static int bdrv_assign_node_name(BlockDriverState *bs,
         return -EINVAL;
     }
 
+    /* takes care of avoiding namespaces collisions */
+    if (bdrv_find(node_name)) {
+        error_setg(errp, "node-name=%s is conflicting with a device id",
+                   node_name);
+        return -EINVAL;
+    }
+
     /* takes care of avoiding duplicates node names */
     if (bdrv_find_node(node_name)) {
         error_setg(errp, "Duplicate node name");
@@ -977,9 +984,8 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
         }
         QDECREF(options);
 
-        bs = bdrv_find(reference);
+        bs = bdrv_lookup_bs(reference, reference, errp);
         if (!bs) {
-            error_setg(errp, "Cannot find block device '%s'", reference);
             return -ENODEV;
         }
         bdrv_ref(bs);

blockdev.c

@@ -452,6 +452,12 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts,
         }
     }
 
+    if (bdrv_find_node(qemu_opts_id(opts))) {
+        error_setg(errp, "device id=%s is conflicting with a node-name",
+                   qemu_opts_id(opts));
+        goto early_err;
+    }
+
     /* init */
     dinfo = g_malloc0(sizeof(*dinfo));
     dinfo->id = g_strdup(qemu_opts_id(opts));