fuse: fix hang under Darwin and FreeBSD when umount

Both FreeBSD and Darwin must use a single reader to access the FUSE device.

Change-Id: I51c467bb0b8e1fda871665d033dd89d11fbe961c

fuse/server.go

@@ -195,14 +195,11 @@ func NewServer(fs RawFileSystem, mountPoint string, opts *MountOptions) (*Server
 	}
 
 	ms := &Server{
-		fileSystem:  fs,
-		opts:        &o,
-		maxReaders:  maxReaders,
-		retrieveTab: make(map[uint64]*retrieveCacheRequest),
-		// OSX has races when multiple routines read from the
-		// FUSE device: on unmount, sometime some reads do not
-		// error-out, meaning that unmount will hang.
-		singleReader: runtime.GOOS == "darwin",
+		fileSystem:   fs,
+		opts:         &o,
+		maxReaders:   maxReaders,
+		retrieveTab:  make(map[uint64]*retrieveCacheRequest),
+		singleReader: useSingleReader,
 		ready:        make(chan error, 1),
 	}
 	ms.reqPool.New = func() interface{} {

fuse/server_linux.go

@@ -8,6 +8,8 @@ import (
 	"syscall"
 )
 
+const useSingleReader = false
+
 func (ms *Server) systemWrite(req *request, header []byte) Status {
 	if req.flatDataSize() == 0 {
 		err := handleEINTR(func() error {

fuse/server_unix.go

@@ -6,6 +6,11 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// OSX and FreeBSD has races when multiple routines read
+// from the FUSE device: on unmount, sometime some reads
+// do not error-out, meaning that unmount will hang.
+const useSingleReader = true
+
 func (ms *Server) systemWrite(req *request, header []byte) Status {
 	if req.flatDataSize() == 0 {
 		err := handleEINTR(func() error {