mount,cmount,mount2: add --direct-io flag to force uncached access

This change adds the --direct-io flag to the mount. This means the
page cache is completely bypassed for reads and writes. No read-ahead
takes place. Shared mmap is disabled.

This is useful to accurately read files which may change length
frequently on the source.

cmd/cmount/fs.go

@@ -27,6 +27,7 @@ const fhUnset = ^uint64(0)
 type FS struct {
 	VFS       *vfs.VFS
 	f         fs.Fs
+	opt       *mountlib.Options
 	ready     chan (struct{})
 	mu        sync.Mutex // to protect the below
 	handles   []vfs.Handle
@@ -34,10 +35,11 @@ type FS struct {
 }
 
 // NewFS makes a new FS
-func NewFS(VFS *vfs.VFS) *FS {
+func NewFS(VFS *vfs.VFS, opt *mountlib.Options) *FS {
 	fsys := &FS{
 		VFS:   VFS,
 		f:     VFS.Fs(),
+		opt:   opt,
 		ready: make(chan (struct{})),
 	}
 	return fsys
@@ -309,6 +311,9 @@ func (fsys *FS) OpenEx(path string, fi *fuse.FileInfo_t) (errc int) {
 	if entry := handle.Node().DirEntry(); entry != nil && entry.Size() < 0 {
 		fi.DirectIo = true
 	}
+	if fsys.opt.DirectIO {
+		fi.DirectIo = true
+	}
 
 	fi.Fh = fsys.openHandle(handle)
 	return 0

cmd/cmount/mount.go

@@ -149,7 +149,7 @@ func mount(VFS *vfs.VFS, mountPath string, opt *mountlib.Options) (<-chan error,
 	fs.Debugf(nil, "Mounting on %q (%q)", mountpoint, opt.VolumeName)
 
 	// Create underlying FS
-	fsys := NewFS(VFS)
+	fsys := NewFS(VFS, opt)
 	host := fuse.NewFileSystemHost(fsys)
 	host.SetCapReaddirPlus(true) // only works on Windows
 	if opt.CaseInsensitive.Valid {

cmd/mount/file.go

@@ -78,6 +78,9 @@ func (f *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenR
 	if entry := handle.Node().DirEntry(); entry != nil && entry.Size() < 0 {
 		resp.Flags |= fuse.OpenDirectIO
 	}
+	if f.fsys.opt.DirectIO {
+		resp.Flags |= fuse.OpenDirectIO
+	}
 
 	return &FileHandle{handle}, nil
 }

cmd/mount2/node.go

@@ -158,6 +158,9 @@ func (n *Node) Open(ctx context.Context, flags uint32) (fh fusefs.FileHandle, fu
 	if entry := n.node.DirEntry(); entry != nil && entry.Size() < 0 {
 		fuseFlags |= fuse.FOPEN_DIRECT_IO
 	}
+	if n.fsys.opt.DirectIO {
+		fuseFlags |= fuse.FOPEN_DIRECT_IO
+	}
 	return newFileHandle(handle, n.fsys), fuseFlags, 0
 }
 

cmd/mountlib/mount.go

@@ -52,6 +52,7 @@ type Options struct {
 	DaemonTimeout      time.Duration // OSXFUSE only
 	AsyncRead          bool
 	NetworkMode        bool // Windows only
+	DirectIO           bool // use Direct IO for file access
 	CaseInsensitive    fs.Tristate
 }
 
@@ -145,6 +146,7 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.BoolVarP(flagSet, &Opt.WritebackCache, "write-back-cache", "", Opt.WritebackCache, "Makes kernel buffer writes before sending them to rclone (without this, writethrough caching is used) (not supported on Windows)", "Mount")
 	flags.StringVarP(flagSet, &Opt.DeviceName, "devname", "", Opt.DeviceName, "Set the device name - default is remote:path", "Mount")
 	flags.FVarP(flagSet, &Opt.CaseInsensitive, "mount-case-insensitive", "", "Tell the OS the mount is case insensitive (true) or sensitive (false) regardless of the backend (auto)", "Mount")
+	flags.BoolVarP(flagSet, &Opt.DirectIO, "direct-io", "", Opt.DirectIO, "Use Direct IO, disables caching of data", "Mount")
 	// Windows and OSX
 	flags.StringVarP(flagSet, &Opt.VolumeName, "volname", "", Opt.VolumeName, "Set the volume name (supported on Windows and OSX only)", "Mount")
 	// OSX only