util: Emancipate id_wellformed() from QemuOpts

IDs have long spread beyond QemuOpts: not everything with an ID
necessarily goes through QemuOpts.  Commit 9aebf3b is about such a
case: block layer names are meant to be well-formed IDs, but some of
them don't go through QemuOpts, and thus weren't checked.  The commit
fixed that the straightforward way: rename the internal QemuOpts
helper id_wellformed() to qemu_opts_id_wellformed() and give it
external linkage.

Instead of using it directly in block.c, the commit adds wrapper
bdrv_is_valid_name(), probably to hide the connection to QemuOpts.

Go one logical step further: emancipate IDs from QemuOpts.  Rename the
function back to id_wellformed(), and put it in another file.  While
there, clean up its value to bool.  Peel off the bdrv_is_valid_name()
wrapper.

[Replaced stray return 0 with return false to match bool returns used
elsewhere in id_wellformed().
--Stefan]

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -335,18 +335,13 @@ void bdrv_register(BlockDriver *bdrv)
     QLIST_INSERT_HEAD(&bdrv_drivers, bdrv, list);
 }
 
-static bool bdrv_is_valid_name(const char *name)
-{
-    return qemu_opts_id_wellformed(name);
-}
-
 /* create a new block device (by default it is empty) */
 BlockDriverState *bdrv_new(const char *device_name, Error **errp)
 {
     BlockDriverState *bs;
     int i;
 
-    if (*device_name && !bdrv_is_valid_name(device_name)) {
+    if (*device_name && !id_wellformed(device_name)) {
         error_setg(errp, "Invalid device name");
         return NULL;
     }
@@ -874,7 +869,7 @@ static void bdrv_assign_node_name(BlockDriverState *bs,
     }
 
     /* Check for empty string or invalid characters */
-    if (!bdrv_is_valid_name(node_name)) {
+    if (!id_wellformed(node_name)) {
         error_setg(errp, "Invalid node name");
         return;
     }