knfsd: allow cache_register to return error on failure

Newer server features such as nfsv4 and gss depend on proc to work, so a
failure to initialize the proc files they need should be treated as
fatal.

Thanks to Andrew Morton for style fix and compile fix in case where
CONFIG_NFSD_V4 is undefined.

Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/export.c

@@ -1637,13 +1637,19 @@ exp_verify_string(char *cp, int max)
 /*
  * Initialize the exports module.
  */
-void
+int
 nfsd_export_init(void)
 {
+	int rv;
 	dprintk("nfsd: initializing export module.\n");
 
-	cache_register(&svc_export_cache);
-	cache_register(&svc_expkey_cache);
+	rv = cache_register(&svc_export_cache);
+	if (rv)
+		return rv;
+	rv = cache_register(&svc_expkey_cache);
+	if (rv)
+		cache_unregister(&svc_export_cache);
+	return rv;
 
 }