auth: fix performance problem when looking up permissions

data_resource lookup uses data_resource::name(), which uses sprint(), which
uses (indirectly) locale, which takes a global lock.  This is a bottleneck
on large machines.

Fix by not using name() during lookup.

Fixes #1419
Message-Id: <1467616296-17645-1-git-send-email-avi@scylladb.com>

auth/auth.cc

@@ -97,7 +97,7 @@ namespace std {
 template <>
 struct hash<auth::data_resource> {
     size_t operator()(const auth::data_resource & v) const {
-        return std::hash<sstring>()(v.name());
+        return v.hash_value();
     }
 };
 

auth/data_resource.hh

@@ -41,6 +41,7 @@
 
 #pragma once
 
+#include "utils/hash.hh"
 #include <iosfwd>
 #include <set>
 #include <seastar/core/sstring.hh>
@@ -137,6 +138,10 @@ public:
 
     bool operator==(const data_resource&) const;
     bool operator<(const data_resource&) const;
+
+    size_t hash_value() const {
+        return utils::tuple_hash()(_ks, _cf);
+    }
 };
 
 /**