Attempt to add passthrough support

Signed-off-by: Anagh Kumar Baranwal <6824881+darthShadow@users.noreply.github.com>

Author: darthShadow

backend/combine/combine.go

@@ -1140,6 +1140,13 @@ func (o *Object) SetTier(tier string) error {
 	return do.SetTier(tier)
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	return 0, fs.ErrorNotImplemented
+}
+
 // Check the interfaces are satisfied
 var (
 	_ fs.Fs              = (*Fs)(nil)

backend/compress/compress.go

@@ -89,7 +89,7 @@ func init() {
 			Help: `GZIP compression level (-2 to 9).
 
 Generally -1 (default, equivalent to 5) is recommended.
-Levels 1 to 9 increase compression at the cost of speed. Going past 6 
+Levels 1 to 9 increase compression at the cost of speed. Going past 6
 generally offers very little return.
 
 Level -2 uses Huffman encoding only. Only use if you know what you
@@ -103,7 +103,7 @@ Level 0 turns off compression.`,
 In this case the compressed file will need to be cached to determine
 it's size.
 
-Files smaller than this limit will be cached in RAM, files larger than 
+Files smaller than this limit will be cached in RAM, files larger than
 this limit will be cached on disk.`,
 			Default:  fs.SizeSuffix(20 * 1024 * 1024),
 			Advanced: true,
@@ -1498,6 +1498,13 @@ func (o *Object) ID() string {
 	return do.ID()
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	return 0, fs.ErrorNotImplemented
+}
+
 // Name of the remote (as passed into NewFs)
 func (f *Fs) Name() string {
 	return f.name

backend/crypt/crypt.go

@@ -144,7 +144,7 @@ problem that should be investigated.`,
 			Name: "filename_encoding",
 			Help: `How to encode the encrypted filename to text string.
 
-This option could help with shortening the encrypted filename. The 
+This option could help with shortening the encrypted filename. The
 suitable option would depend on the way your remote count the filename
 length and if it's case sensitive.`,
 			Default: "base32",
@@ -167,7 +167,7 @@ length and if it's case sensitive.`,
 			Name: "suffix",
 			Help: `If this is set it will override the default suffix of ".bin".
 
-Setting suffix to "none" will result in an empty suffix. This may be useful 
+Setting suffix to "none" will result in an empty suffix. This may be useful
 when the path length is critical.`,
 			Default:  ".bin",
 			Advanced: true,
@@ -1268,6 +1268,13 @@ func (o *Object) MimeType(ctx context.Context) string {
 	return ""
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	return 0, fs.ErrorNotImplemented
+}
+
 // Check the interfaces are satisfied
 var (
 	_ fs.Fs              = (*Fs)(nil)

backend/hasher/hasher.go

@@ -546,6 +546,17 @@ func (o *Object) SetMetadata(ctx context.Context, metadata fs.Metadata) error {
 	return do.SetMetadata(ctx, metadata)
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	do, ok := o.Object.(fs.Fder)
+	if !ok {
+		return 0, fs.ErrorNotImplemented
+	}
+	return do.Fd(ctx, flags)
+}
+
 // Check the interfaces are satisfied
 var (
 	_ fs.Fs              = (*Fs)(nil)

backend/local/local.go

@@ -1713,6 +1713,19 @@ func cleanRootPath(s string, noUNC bool, enc encoder.MultiEncoder) string {
 	return s
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	osFile, err := file.OpenFile(o.path, flags, 0)
+	if err != nil {
+		return 0, fmt.Errorf("failed to open file: %s: %w", o.path, err)
+	}
+	fileFd := osFile.Fd()
+	fs.Infof(o, "Returning fd: %s: %d", o.path, fileFd)
+	return fileFd, nil
+}
+
 // Items returns the count of items in this directory or this
 // directory and subdirectories if known, -1 for unknown
 func (d *Directory) Items() int64 {

backend/union/entry.go

@@ -219,6 +219,17 @@ func (d *Directory) ModTime(ctx context.Context) (t time.Time) {
 	return t
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	do, ok := o.Object.Object.(fs.Fder)
+	if !ok {
+		return 0, fs.ErrorNotImplemented
+	}
+	return do.Fd(ctx, flags)
+}
+
 // Size returns the size of the directory
 // It returns the sum of all candidates
 func (d *Directory) Size() (s int64) {

backend/union/upstream/upstream.go

@@ -333,6 +333,17 @@ func (o *Object) SetMetadata(ctx context.Context, metadata fs.Metadata) error {
 	return do.SetMetadata(ctx, metadata)
 }
 
+// Fd returns the Fd of the Object
+//
+// It should return fs.ErrorNotImplemented if it's not available
+func (o *Object) Fd(ctx context.Context, flags int) (uintptr, error) {
+	do, ok := o.Object.(fs.Fder)
+	if !ok {
+		return 0, fs.ErrorNotImplemented
+	}
+	return do.Fd(ctx, flags)
+}
+
 // Metadata returns metadata for an DirEntry
 //
 // It should return nil if there is no Metadata

cmd/mount2/file.go

@@ -149,3 +149,19 @@ func (f *FileHandle) Setattr(ctx context.Context, in *fuse.SetAttrIn, out *fuse.
 }
 
 var _ fusefs.FileSetattrer = (*FileHandle)(nil)
+
+// PassthroughFd returns the file descriptor of the file if the remote supports passthrough
+func (f *FileHandle) PassthroughFd() (int, bool) {
+	_, ok := f.h.Node().(*vfs.File)
+	if !ok {
+		return 0, false
+	}
+
+	fileFd := f.h.Fd()
+	if fileFd == 0 {
+		return 0, false
+	}
+	return int(fileFd), true
+}
+
+var _ fusefs.FilePassthroughFder = (*FileHandle)(nil)

cmd/mount2/mount.go

@@ -33,6 +33,7 @@ func mountOptions(fsys *FS, f fs.Fs, opt *mountlib.Options) (mountOpts *fuse.Mou
 		MaxReadAhead:       int(fsys.opt.MaxReadAhead),
 		MaxWrite:           1024 * 1024, // Linux v4.20+ caps requests at 1 MiB
 		DisableReadDirPlus: true,
+		MaxStackDepth:      fsys.opt.MaxStackDepth,
 
 		// RememberInodes: true,
 		// SingleThreaded: true,

cmd/mountlib/mount.go

@@ -118,10 +118,15 @@ var OptionsInfo = fs.Options{{
 	Default: fs.Tristate{},
 	Help:    "Tell the OS the mount is case insensitive (true) or sensitive (false) regardless of the backend (auto)",
 	Groups:  "Mount",
+}, {
+	Name:    "max_stack_depth",
+	Default: 1,
+	Help:    "Maximum stacking depth for passthrough files. Defaults to 1",
+	Groups:  "Mount",
 }, {
 	Name:    "direct_io",
 	Default: false,
-	Help:    "Use Direct IO, disables caching of data",
+	Help:    "Use Direct IO, disables the page cache",
 	Groups:  "Mount",
 }, {
 	Name:    "volname",
@@ -189,6 +194,7 @@ type Options struct {
 	NetworkMode        bool          `config:"network_mode"` // Windows only
 	DirectIO           bool          `config:"direct_io"`    // use Direct IO for file access
 	CaseInsensitive    fs.Tristate   `config:"mount_case_insensitive"`
+	MaxStackDepth      int           `config:"max_stack_depth"`
 }
 
 type (