From 1478d6b7e2eff41f19fac1ca62593d545b360893 Mon Sep 17 00:00:00 2001
From: Bob Nystrom <robert@stuffwithstuff.com>
Date: Wed, 16 Mar 2016 07:27:03 -0700
Subject: [PATCH] Add a few comments.

---
 src/module/io.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/module/io.c b/src/module/io.c
index f094cb18..428d9f62 100644
--- a/src/module/io.c
+++ b/src/module/io.c
@@ -10,13 +10,20 @@
 #include <stdio.h>
 #include <fcntl.h>
 
+// Windows doesn't define all of the Unix permission and mode flags by default,
+// so map them ourselves.
 #if defined(WIN32) || defined(WIN64)
-#include <sys\stat.h>
-#define S_IRUSR _S_IREAD 
-#define S_IWUSR _S_IWRITE
-#define O_SYNC 0
-#define S_ISREG(m) (((m) & S_IFMT) == S_IFREG)
-#define S_ISDIR(m) (((m) & S_IFMT) == S_IFDIR)
+  #include <sys\stat.h>
+
+  // Map to Windows permission flags.
+  #define S_IRUSR _S_IREAD
+  #define S_IWUSR _S_IWRITE
+
+  #define S_ISREG(m) (((m) & S_IFMT) == S_IFREG)
+  #define S_ISDIR(m) (((m) & S_IFMT) == S_IFDIR)
+
+  // Not supported on Windows.
+  #define O_SYNC 0
 #endif
 
 typedef struct sFileRequestData
@@ -203,9 +210,7 @@ static int mapFileFlags(int flags)
   if (flags & 0x01) result |= O_RDONLY;
   if (flags & 0x02) result |= O_WRONLY;
   if (flags & 0x04) result |= O_RDWR;
-#ifdef O_SYNC
   if (flags & 0x08) result |= O_SYNC;
-#endif
   if (flags & 0x10) result |= O_CREAT;
   if (flags & 0x20) result |= O_TRUNC;
   if (flags & 0x40) result |= O_EXCL;