src: add O_NOATIME constant

Add O_NOATIME flag on Linux for use with `fs.open()`.

PR-URL: https://github.com/nodejs/node/pull/6492
Fixes: https://github.com/nodejs/node/issues/2182
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/node_constants.cc

@@ -1036,6 +1036,10 @@ void DefineSystemConstants(Local<Object> target) {
   NODE_DEFINE_CONSTANT(target, O_EXCL);
 #endif
 
+#ifdef O_NOATIME
+  NODE_DEFINE_CONSTANT(target, O_NOATIME);
+#endif
+
 #ifdef O_NOFOLLOW
   NODE_DEFINE_CONSTANT(target, O_NOFOLLOW);
 #endif

test/parallel/test-process-constants-noatime.js

@@ -0,0 +1,11 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+const isLinux = process.platform === 'linux';
+
+const O_NOATIME = process.binding('constants').O_NOATIME;
+const expected = isLinux ? 0x40000 : undefined;
+
+assert.strictEqual(O_NOATIME, expected);