Back out "fuse: remove Server.ready channel"

This backs out commit f829e36.

Reason: the Server.ready channel is necessary on OSX. Document why.

Change-Id: I9cde964882f66c98cb726a343fad93c3929750e4

fuse/mount_darwin.go

@@ -26,7 +26,7 @@ func unixgramSocketpair() (l, r *os.File, err error) {
 
 // Create a FUSE FS on the specified mount point.  The returned
 // mount point is always absolute.
-func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
+func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {
 	local, remote, err := unixgramSocketpair()
 	if err != nil {
 		return
@@ -65,9 +65,14 @@ func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
 	if err != nil {
 		return -1, err
 	}
-	ready := make(chan error, 1)
+
 	go func() {
-		// wait inside a goroutine or otherwise it would block forever for unknown reasons
+		// On macos, mount_osxfuse is not just a suid
+		// wrapper. It interacts with the FS setup, and will
+		// not exit until the filesystem has successfully
+		// responded to INIT and STATFS. This means we can
+		// only wait on the mount_osxfuse process after the
+		// server has fully started
 		if err := cmd.Wait(); err != nil {
 			err = fmt.Errorf("mount_osxfusefs failed: %v. Stderr: %s, Stdout: %s",
 				err, errOut.String(), out.String())
@@ -81,9 +86,7 @@ func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
 	// acquired through normal operations (e.g. open).
 	// Buf for fd, we have to set CLOEXEC manually
 	syscall.CloseOnExec(fd)
-	if err == nil {
-		err = <-ready
-	}
+
 	return fd, err
 }
 

fuse/mount_freebsd.go

@@ -41,7 +41,7 @@ func callMountFuseFs(mountPoint string, opts *MountOptions) (fd int, err error)
 	return int(f.Fd()), nil
 }
 
-func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
+func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {
 	// Using the same logic from libfuse to prevent chaos
 	for {
 		f, err := os.OpenFile("/dev/null", os.O_RDWR, 0o000)
@@ -74,6 +74,7 @@ func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
 	// Buf for fd, we have to set CLOEXEC manually
 	syscall.CloseOnExec(fd)
 
+	close(ready)
 	return fd, err
 }
 

fuse/mount_linux.go

@@ -27,7 +27,7 @@ func unixgramSocketpair() (l, r *os.File, err error) {
 
 // Create a FUSE FS on the specified mount point without using
 // fusermount.
-func mountDirect(mountPoint string, opts *MountOptions) (fd int, err error) {
+func mountDirect(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {
 	fd, err = syscall.Open("/dev/fuse", os.O_RDWR, 0) // use syscall.Open since we want an int fd
 	if err != nil {
 		return
@@ -76,6 +76,8 @@ func mountDirect(mountPoint string, opts *MountOptions) (fd int, err error) {
 		return
 	}
 
+	// success
+	close(ready)
 	return
 }
 
@@ -135,9 +137,9 @@ func callFusermount(mountPoint string, opts *MountOptions) (fd int, err error) {
 
 // Create a FUSE FS on the specified mount point.  The returned
 // mount point is always absolute.
-func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
+func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {
 	if opts.DirectMount || opts.DirectMountStrict {
-		fd, err := mountDirect(mountPoint, opts)
+		fd, err := mountDirect(mountPoint, opts, ready)
 		if err == nil {
 			return fd, nil
 		} else if opts.Debug {
@@ -166,6 +168,7 @@ func mount(mountPoint string, opts *MountOptions) (fd int, err error) {
 	// acquired through normal operations (e.g. open).
 	// Buf for fd, we have to set CLOEXEC manually
 	syscall.CloseOnExec(fd)
+	close(ready)
 	return fd, err
 }
 

fuse/server.go

@@ -77,6 +77,9 @@ type Server struct {
 	loops        sync.WaitGroup
 	serving      bool // for preventing duplicate Serve() calls
 
+	// Used to implement WaitMount on macos.
+	ready chan error
+
 	// for implementing single threaded processing.
 	requestProcessingMu sync.Mutex
 
@@ -209,6 +212,7 @@ func NewServer(fs RawFileSystem, mountPoint string, opts *MountOptions) (*Server
 		maxReaders:   maxReaders,
 		retrieveTab:  make(map[uint64]*retrieveCacheRequest),
 		singleReader: useSingleReader,
+		ready:        make(chan error, 1),
 	}
 	ms.reqPool.New = func() interface{} {
 		return &requestAlloc{
@@ -238,7 +242,7 @@ func NewServer(fs RawFileSystem, mountPoint string, opts *MountOptions) (*Server
 		}
 		mountPoint = filepath.Clean(filepath.Join(cwd, mountPoint))
 	}
-	fd, err := mount(mountPoint, &o)
+	fd, err := mount(mountPoint, &o, ms.ready)
 	if err != nil {
 		return nil, err
 	}
@@ -995,6 +999,10 @@ func (in *InitIn) supportsRenameSwap() bool {
 // avoid racing between accessing the (empty or not yet mounted)
 // mountpoint, and the OS trying to setup the user-space mount.
 func (ms *Server) WaitMount() error {
+	err := <-ms.ready
+	if err != nil {
+		return err
+	}
 	if parseFuseFd(ms.mountPoint) >= 0 {
 		// Magic `/dev/fd/N` mountpoint. We don't know the real mountpoint, so
 		// we cannot run the poll hack.