fuse: move Flags2 handling to platform specific code

Document why some bits are platform dependent.

Change-Id: Ib8bde502a3450028f4d87ba61fa9c76ea3ea6c63

fuse/types.go

@@ -299,6 +299,7 @@ const (
 	CAP_MAX_PAGES        = (1 << 22)
 	CAP_CACHE_SYMLINKS   = (1 << 23)
 
+	/* bits 24..31 differ across linux and mac */
 	/* bits 32..63 get shifted down 32 bits into the Flags2 field */
 	CAP_SECURITY_CTX      = (1 << 32)
 	CAP_HAS_INODE_DAX     = (1 << 33)
@@ -337,11 +338,6 @@ type InitOut struct {
 	Unused              [6]uint32
 }
 
-func (o *InitOut) setFlags(flags uint64) {
-	o.Flags = uint32(flags)
-	o.Flags2 = uint32(flags >> 32)
-}
-
 type _CuseInitIn struct {
 	InHeader
 	Major  uint32

fuse/types_darwin.go

@@ -125,3 +125,7 @@ func (s *StatfsOut) FromStatfsT(statfs *syscall.Statfs_t) {
 		s.Bavail /= adj
 	}
 }
+
+func (o *InitOut) setFlags(flags uint64) {
+	o.Flags = uint32(flags)
+}

fuse/types_linux.go

@@ -45,3 +45,8 @@ func (s *StatfsOut) FromStatfsT(statfs *syscall.Statfs_t) {
 	s.Frsize = uint32(statfs.Frsize)
 	s.NameLen = uint32(statfs.Namelen)
 }
+
+func (o *InitOut) setFlags(flags uint64) {
+	o.Flags = uint32(flags) | CAP_INIT_EXT
+	o.Flags2 = uint32(flags >> 32)
+}