Expand comments and reorganize; remove mistaken redefine of DISPATCH_EXPORT macros

Author: dgrove-oss

os/linux_base.h

@@ -69,10 +69,18 @@ typedef void (*dispatch_mach_handler_function_t)(void*, dispatch_mach_reason_t,
 
 typedef void (*dispatch_mach_msg_destructor_t)(void*);
 
+typedef uint32_t voucher_activity_mode_t;
+
+struct voucher_offsets_s {
+  uint32_t vo_version;
+};
+
+
 /*
  * Stub out defines for other missing types
  */
 
+// Pulled from OS X man page for kevent
 struct kevent64_s {
     uint64_t        ident;          /* identifier for this event */
     int16_t         filter;         /* filter for event */
@@ -83,17 +91,13 @@ struct kevent64_s {
     uint64_t        ext[2];         /* filter-specific extensions */
 };
 
-typedef uint32_t voucher_activity_mode_t;
-
-struct voucher_offsets_s {
-  uint32_t vo_version;
-};
-
 
-// bogus...
+// PAGE_SIZE and SIZE_T_MAX should not be hardcoded like this here.
 #define PAGE_SIZE (4096)
 #define SIZE_T_MAX (0x7fffffff)
 
+// Define to 0 the NOTE_ values that are not present on Linux.
+// Revisit this...would it be better to ifdef out the uses instead??
 #define NOTE_VM_PRESSURE 0
 #define NOTE_ABSOLUTE 0
 #define NOTE_NSECONDS 0
@@ -110,16 +114,6 @@ struct voucher_offsets_s {
 #endif
 #define OS_EXPORT
 
-#ifdef DISPATCH_EXPORT
-#undef DISPATCH_EXPORT
-#endif 
-#define DISPATCH_EXPORT
-
-#ifdef DISPATCH_NONNULL_ALL 
-#undef DISPATCH_NONNULL_ALL 
-#endif
-#define DISPATCH_NONNULL_ALL 
-
 #ifdef OS_WARN_RESULT_NEEDS_RELEASE 
 #undef OS_WARN_RESULT_NEEDS_RELEASE  
 #endif
@@ -135,7 +129,8 @@ struct voucher_offsets_s {
 #define OS_NOTHROW
 
 
-// NOTE (Dave), these and similar macros come from Availabity.h on OS X
+// These and similar macros come from Availabilty.h on OS X
+// Need a better way to do this long term.
 #define __OSX_AVAILABLE_BUT_DEPRECATED(a,b,c,d) //
 #define __OSX_AVAILABLE_BUT_DEPRECATED_MSG(a,b,c,d,msg) //