uuid: annotate non-null requirements

Coverity already saw through a NULL dereference without these
annotations, and gcc is still too puny to do good NULL analysis.
But clang still benefits (and is easier to run than coverity),
not to mention that adding this bit of documentation to the code
may help future developers remember the constraints.

* src/util/uuid.h (virGetHostUUID, virUUIDFormat): Document
restrictions, for improved static analysis.

src/util/uuid.h

 /*
- * Copyright (C) 2007 Red Hat, Inc.
+ * Copyright (C) 2007, 2011 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -22,8 +22,10 @@
 #ifndef __VIR_UUID_H__
 # define __VIR_UUID_H__
 
+# include "internal.h"
+
 int virSetHostUUIDStr(const char *host_uuid);
-int virGetHostUUID(unsigned char *host_uuid);
+int virGetHostUUID(unsigned char *host_uuid) ATTRIBUTE_NONNULL(1);
 
 int virUUIDIsValid(unsigned char *uuid);
 
@@ -33,6 +35,6 @@ int virUUIDParse(const char *uuidstr,
                  unsigned char *uuid);
 
 void virUUIDFormat(const unsigned char *uuid,
-                   char *uuidstr);
+                   char *uuidstr) ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 
 #endif /* __VIR_UUID_H__ */