serve nbd: serve an rclone remote as a Network Block Device - WIP FIXME

TODO

- Need to finalise rclone/gonbdserver and upload and change go.mod/go.sum
- Remove uneeded dependencies from rclone/gonbdserver

Maybe make companion `mount nbd` command?

Fixes #7337

cmd/serve/nbd/chunked_backend.go

@@ -0,0 +1,140 @@
+// Implements an nbd.Backend for serving from a chunked file in the VFS.
+
+package nbd
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/rclone/gonbdserver/nbd"
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/log"
+	"github.com/rclone/rclone/vfs/chunked"
+	"golang.org/x/net/context"
+)
+
+// Backend for a single chunked file
+type chunkedBackend struct {
+	file *chunked.File
+	ec   *nbd.ExportConfig
+}
+
+// Create Backend for a single chunked file
+type chunkedBackendFactory struct {
+	s    *NBD
+	file *chunked.File
+}
+
+// WriteAt implements Backend.WriteAt
+func (cb *chunkedBackend) WriteAt(ctx context.Context, b []byte, offset int64, fua bool) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", len(b), offset)("n=%d, err=%v", &n, &err)
+	n, err = cb.file.WriteAt(b, offset)
+	if err != nil || !fua {
+		return n, err
+	}
+	err = cb.file.Sync()
+	if err != nil {
+		return 0, err
+	}
+	return n, err
+}
+
+// ReadAt implements Backend.ReadAt
+func (cb *chunkedBackend) ReadAt(ctx context.Context, b []byte, offset int64) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", len(b), offset)("n=%d, err=%v", &n, &err)
+	return cb.file.ReadAt(b, offset)
+}
+
+// TrimAt implements Backend.TrimAt
+func (cb *chunkedBackend) TrimAt(ctx context.Context, length int, offset int64) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", length, offset)("n=%d, err=%v", &n, &err)
+	return length, nil
+}
+
+// Flush implements Backend.Flush
+func (cb *chunkedBackend) Flush(ctx context.Context) (err error) {
+	defer log.Trace(logPrefix, "")("err=%v", &err)
+	return nil
+}
+
+// Close implements Backend.Close
+func (cb *chunkedBackend) Close(ctx context.Context) (err error) {
+	defer log.Trace(logPrefix, "")("err=%v", &err)
+	err = cb.file.Close()
+	return nil
+}
+
+// Geometry implements Backend.Geometry
+func (cb *chunkedBackend) Geometry(ctx context.Context) (size uint64, minBS uint64, prefBS uint64, maxBS uint64, err error) {
+	defer log.Trace(logPrefix, "")("size=%d, minBS=%d, prefBS=%d, maxBS=%d, err=%v", &size, &minBS, &prefBS, &maxBS, &err)
+	size = uint64(cb.file.Size())
+	minBS = cb.ec.MinimumBlockSize
+	prefBS = cb.ec.PreferredBlockSize
+	maxBS = cb.ec.MaximumBlockSize
+	err = nil
+	return
+}
+
+// HasFua implements Backend.HasFua
+func (cb *chunkedBackend) HasFua(ctx context.Context) (fua bool) {
+	defer log.Trace(logPrefix, "")("fua=%v", &fua)
+	return true
+}
+
+// HasFlush implements Backend.HasFua
+func (cb *chunkedBackend) HasFlush(ctx context.Context) (flush bool) {
+	defer log.Trace(logPrefix, "")("flush=%v", &flush)
+	return true
+}
+
+// New generates a new chunked backend
+func (cbf *chunkedBackendFactory) newBackend(ctx context.Context, ec *nbd.ExportConfig) (nbd.Backend, error) {
+	err := cbf.file.Open(false, 0)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open chunked file: %w", err)
+	}
+	cb := &chunkedBackend{
+		file: cbf.file,
+		ec:   ec,
+	}
+	return cb, nil
+}
+
+// Generate a chunked backend factory
+func (s *NBD) newChunkedBackendFactory(ctx context.Context) (bf backendFactory, err error) {
+	create := s.opt.Create > 0
+	if s.vfs.Opt.ReadOnly && create {
+		return nil, errors.New("can't create files with --read-only")
+	}
+	file := chunked.New(s.vfs, s.leaf)
+	err = file.Open(create, s.log2ChunkSize)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open chunked file: %w", err)
+	}
+	defer fs.CheckClose(file, &err)
+	var truncateSize fs.SizeSuffix
+	if create {
+		if file.Size() == 0 {
+			truncateSize = s.opt.Create
+		}
+	} else {
+		truncateSize = s.opt.Resize
+	}
+	if truncateSize > 0 {
+		err = file.Truncate(int64(truncateSize))
+		if err != nil {
+			return nil, fmt.Errorf("failed to create chunked file: %w", err)
+		}
+		fs.Logf(logPrefix, "Size of network block device is now %v", truncateSize)
+	}
+	return &chunkedBackendFactory{
+		s:    s,
+		file: file,
+	}, nil
+}
+
+// Check interfaces
+var (
+	_ nbd.Backend    = (*chunkedBackend)(nil)
+	_ backendFactory = (*chunkedBackendFactory)(nil)
+)

cmd/serve/nbd/file_backend.go

@@ -0,0 +1,140 @@
+// Implements an nbd.Backend for serving from the VFS.
+
+package nbd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/rclone/gonbdserver/nbd"
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/log"
+	"github.com/rclone/rclone/vfs"
+	"golang.org/x/net/context"
+)
+
+// Backend for a single file
+type fileBackend struct {
+	file vfs.Handle
+	ec   *nbd.ExportConfig
+}
+
+// Create Backend for a single file
+type fileBackendFactory struct {
+	s        *NBD
+	vfs      *vfs.VFS
+	filePath string
+	perms    int
+}
+
+// WriteAt implements Backend.WriteAt
+func (fb *fileBackend) WriteAt(ctx context.Context, b []byte, offset int64, fua bool) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", len(b), offset)("n=%d, err=%v", &n, &err)
+	n, err = fb.file.WriteAt(b, offset)
+	if err != nil || !fua {
+		return n, err
+	}
+	err = fb.file.Sync()
+	if err != nil {
+		return 0, err
+	}
+	return n, err
+}
+
+// ReadAt implements Backend.ReadAt
+func (fb *fileBackend) ReadAt(ctx context.Context, b []byte, offset int64) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", len(b), offset)("n=%d, err=%v", &n, &err)
+	return fb.file.ReadAt(b, offset)
+}
+
+// TrimAt implements Backend.TrimAt
+func (fb *fileBackend) TrimAt(ctx context.Context, length int, offset int64) (n int, err error) {
+	defer log.Trace(logPrefix, "size=%d, off=%d", length, offset)("n=%d, err=%v", &n, &err)
+	return length, nil
+}
+
+// Flush implements Backend.Flush
+func (fb *fileBackend) Flush(ctx context.Context) (err error) {
+	defer log.Trace(logPrefix, "")("err=%v", &err)
+	return nil
+}
+
+// Close implements Backend.Close
+func (fb *fileBackend) Close(ctx context.Context) (err error) {
+	defer log.Trace(logPrefix, "")("err=%v", &err)
+	err = fb.file.Close()
+	return nil
+}
+
+// Geometry implements Backend.Geometry
+func (fb *fileBackend) Geometry(ctx context.Context) (size uint64, minBS uint64, prefBS uint64, maxBS uint64, err error) {
+	defer log.Trace(logPrefix, "")("size=%d, minBS=%d, prefBS=%d, maxBS=%d, err=%v", &size, &minBS, &prefBS, &maxBS, &err)
+	fi, err := fb.file.Stat()
+	if err != nil {
+		err = fmt.Errorf("failed read info about open backing file: %w", err)
+		return
+	}
+	size = uint64(fi.Size())
+	minBS = fb.ec.MinimumBlockSize
+	prefBS = fb.ec.PreferredBlockSize
+	maxBS = fb.ec.MaximumBlockSize
+	err = nil
+	return
+}
+
+// HasFua implements Backend.HasFua
+func (fb *fileBackend) HasFua(ctx context.Context) (fua bool) {
+	defer log.Trace(logPrefix, "")("fua=%v", &fua)
+	return true
+}
+
+// HasFlush implements Backend.HasFua
+func (fb *fileBackend) HasFlush(ctx context.Context) (flush bool) {
+	defer log.Trace(logPrefix, "")("flush=%v", &flush)
+	return true
+}
+
+// open the backing file
+func (fbf *fileBackendFactory) open() (vfs.Handle, error) {
+	return fbf.vfs.OpenFile(fbf.filePath, fbf.perms, 0700)
+}
+
+// New generates a new file backend
+func (fbf *fileBackendFactory) newBackend(ctx context.Context, ec *nbd.ExportConfig) (nbd.Backend, error) {
+	fd, err := fbf.open()
+	if err != nil {
+		return nil, fmt.Errorf("failed to open backing file: %w", err)
+	}
+	fb := &fileBackend{
+		file: fd,
+		ec:   ec,
+	}
+	return fb, nil
+}
+
+// Generate a file backend factory
+func (s *NBD) newFileBackendFactory(ctx context.Context) (bf backendFactory, err error) {
+	perms := os.O_RDWR
+	if s.vfs.Opt.ReadOnly {
+		perms = os.O_RDONLY
+	}
+	fbf := &fileBackendFactory{
+		s:        s,
+		vfs:      s.vfs,
+		perms:    perms,
+		filePath: s.leaf,
+	}
+	// Try opening the file so we get errors now rather than later when they are more difficult to report.
+	fd, err := fbf.open()
+	if err != nil {
+		return nil, fmt.Errorf("failed to open backing file: %w", err)
+	}
+	defer fs.CheckClose(fd, &err)
+	return fbf, nil
+}
+
+// Check interfaces
+var (
+	_ nbd.Backend    = (*fileBackend)(nil)
+	_ backendFactory = (*fileBackendFactory)(nil)
+)

cmd/serve/nbd/nbd.go

@@ -0,0 +1,260 @@
+// Package nbd provides a network block device server
+package nbd
+
+import (
+	"bufio"
+	"context"
+	_ "embed"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"math/bits"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/rclone/gonbdserver/nbd"
+	"github.com/rclone/rclone/cmd"
+	"github.com/rclone/rclone/cmd/serve/proxy/proxyflags"
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/config/flags"
+	"github.com/rclone/rclone/lib/systemd"
+	"github.com/rclone/rclone/vfs"
+	"github.com/rclone/rclone/vfs/vfscommon"
+	"github.com/rclone/rclone/vfs/vfsflags"
+	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
+)
+
+const logPrefix = "nbd"
+
+// OptionsInfo descripts the Options in use
+var OptionsInfo = fs.Options{{
+	Name:    "addr",
+	Default: "localhost:10809",
+	Help:    "IPaddress:Port or :Port to bind server to",
+}, {
+	Name:    "min_block_size",
+	Default: fs.SizeSuffix(512), // FIXME
+	Help:    "Minimum block size to advertise",
+}, {
+	Name:    "preferred_block_size",
+	Default: fs.SizeSuffix(4096), // FIXME this is the max according to nbd-client
+	Help:    "Preferred block size to advertise",
+}, {
+	Name:    "max_block_size",
+	Default: fs.SizeSuffix(1024 * 1024), // FIXME,
+	Help:    "Maximum block size to advertise",
+}, {
+	Name:    "create",
+	Default: fs.SizeSuffix(-1),
+	Help:    "If the destination does not exist, create it with this size",
+}, {
+	Name:    "chunk_size",
+	Default: fs.SizeSuffix(0),
+	Help:    "If creating the destination use this chunk size. Must be a power of 2.",
+}, {
+	Name:    "resize",
+	Default: fs.SizeSuffix(-1),
+	Help:    "If the destination exists, resize it to this size",
+}}
+
+// name := flag.String("name", "default", "Export name")
+// description := flag.String("description", "The default export", "Export description")
+
+// Options required for nbd server
+type Options struct {
+	ListenAddr         string        `config:"addr"` // Port to listen on
+	MinBlockSize       fs.SizeSuffix `config:"min_block_size"`
+	PreferredBlockSize fs.SizeSuffix `config:"preferred_block_size"`
+	MaxBlockSize       fs.SizeSuffix `config:"max_block_size"`
+	Create             fs.SizeSuffix `config:"create"`
+	ChunkSize          fs.SizeSuffix `config:"chunk_size"`
+	Resize             fs.SizeSuffix `config:"resize"`
+}
+
+func init() {
+	fs.RegisterGlobalOptions(fs.OptionsInfo{Name: "nbd", Opt: &Opt, Options: OptionsInfo})
+}
+
+// Opt is options set by command line flags
+var Opt Options
+
+// AddFlags adds flags for the nbd
+func AddFlags(flagSet *pflag.FlagSet, Opt *Options) {
+	flags.AddFlagsFromOptions(flagSet, "", OptionsInfo)
+}
+
+func init() {
+	flagSet := Command.Flags()
+	vfsflags.AddFlags(flagSet)
+	proxyflags.AddFlags(flagSet)
+	AddFlags(flagSet, &Opt)
+}
+
+//go:embed nbd.md
+var helpText string
+
+// Command definition for cobra
+var Command = &cobra.Command{
+	Use:   "nbd remote:path",
+	Short: `Serve the remote over NBD.`,
+	Long:  helpText + vfs.Help(),
+	Annotations: map[string]string{
+		"versionIntroduced": "v1.65",
+		"status":            "experimental",
+	},
+	Run: func(command *cobra.Command, args []string) {
+		// FIXME could serve more than one nbd?
+		cmd.CheckArgs(1, 1, command, args)
+		f, leaf := cmd.NewFsFile(args[0])
+
+		cmd.Run(false, true, command, func() error {
+			s, err := run(context.Background(), f, leaf, Opt)
+			if err != nil {
+				log.Fatal(err)
+			}
+
+			defer systemd.Notify()()
+			// FIXME
+			_ = s
+			s.Wait()
+			return nil
+		})
+	},
+}
+
+// NBD contains everything to run the server
+type NBD struct {
+	f                fs.Fs
+	leaf             string
+	vfs              *vfs.VFS // don't use directly, use getVFS
+	opt              Options
+	wg               sync.WaitGroup
+	sessionWaitGroup sync.WaitGroup
+	logRd            *io.PipeReader
+	logWr            *io.PipeWriter
+	log2ChunkSize    uint
+	readOnly         bool // Set for read only by vfs config
+
+	backendFactory backendFactory
+}
+
+// interface for creating backend factories
+type backendFactory interface {
+	newBackend(ctx context.Context, ec *nbd.ExportConfig) (nbd.Backend, error)
+}
+
+// Create and start the server for nbd either on directory f or using file leaf in f
+func run(ctx context.Context, f fs.Fs, leaf string, opt Options) (s *NBD, err error) {
+	s = &NBD{
+		f:        f,
+		leaf:     leaf,
+		opt:      opt,
+		vfs:      vfs.New(f, &vfscommon.Opt),
+		readOnly: vfscommon.Opt.ReadOnly,
+	}
+
+	if opt.ChunkSize != 0 {
+		if set := bits.OnesCount64(uint64(opt.ChunkSize)); set != 1 {
+			return nil, fmt.Errorf("--chunk-size must be a power of 2 (counted %d bits set)", set)
+		}
+		s.log2ChunkSize = uint(bits.TrailingZeros64(uint64(opt.ChunkSize)))
+		fs.Debugf(logPrefix, "Using ChunkSize %v (%v), Log2ChunkSize %d", opt.ChunkSize, fs.SizeSuffix(1<<s.log2ChunkSize), s.log2ChunkSize)
+	}
+	if !vfscommon.Opt.ReadOnly && vfscommon.Opt.CacheMode < vfscommon.CacheModeWrites {
+		return nil, errors.New("need --vfs-cache-mode writes or full when serving read/write")
+	}
+
+	// Create the backend factory
+	if leaf != "" {
+		s.backendFactory, err = s.newFileBackendFactory(ctx)
+	} else {
+		s.backendFactory, err = s.newChunkedBackendFactory(ctx)
+	}
+	if err != nil {
+		return nil, err
+	}
+	nbd.RegisterBackend("rclone", s.backendFactory.newBackend)
+	fs.Debugf(logPrefix, "Registered backends: %v", nbd.GetBackendNames())
+
+	var (
+		protocol = "tcp"
+		addr     = Opt.ListenAddr
+	)
+	if strings.HasPrefix(addr, "unix://") || filepath.IsAbs(addr) {
+		protocol = "unix"
+		addr = strings.TrimPrefix(addr, "unix://")
+
+	}
+
+	ec := nbd.ExportConfig{
+		Name:               "default",
+		Description:        fs.ConfigString(f),
+		Driver:             "rclone",
+		ReadOnly:           vfscommon.Opt.ReadOnly,
+		Workers:            8,     // should this be --checkers or a new config flag FIXME
+		TLSOnly:            false, // FIXME
+		MinimumBlockSize:   uint64(Opt.MinBlockSize),
+		PreferredBlockSize: uint64(Opt.PreferredBlockSize),
+		MaximumBlockSize:   uint64(Opt.MaxBlockSize),
+		DriverParameters: nbd.DriverParametersConfig{
+			"sync": "false",
+			"path": "/tmp/diskimage",
+		},
+	}
+
+	// Make a logger to feed gonbdserver's logs into rclone's logging system
+	s.logRd, s.logWr = io.Pipe()
+	go func() {
+		scanner := bufio.NewScanner(s.logRd)
+		for scanner.Scan() {
+			line := scanner.Text()
+			if s, ok := strings.CutPrefix(line, "[DEBUG] "); ok {
+				fs.Debugf(logPrefix, "%s", s)
+			} else if s, ok := strings.CutPrefix(line, "[INFO] "); ok {
+				fs.Infof(logPrefix, "%s", s)
+			} else if s, ok := strings.CutPrefix(line, "[WARN] "); ok {
+				fs.Logf(logPrefix, "%s", s)
+			} else if s, ok := strings.CutPrefix(line, "[ERROR] "); ok {
+				fs.Errorf(logPrefix, "%s", s)
+			} else if s, ok := strings.CutPrefix(line, "[CRIT] "); ok {
+				fs.Errorf(logPrefix, "%s", s)
+			} else {
+				fs.Infof(logPrefix, "%s", line)
+			}
+		}
+		if err := scanner.Err(); err != nil {
+			fs.Errorf(logPrefix, "Log writer failed: %v", err)
+		}
+	}()
+	logger := log.New(s.logWr, "", 0)
+
+	ci := fs.GetConfig(ctx)
+	dump := ci.Dump & (fs.DumpHeaders | fs.DumpBodies | fs.DumpAuth | fs.DumpRequests | fs.DumpResponses)
+	var serverConfig = nbd.ServerConfig{
+		Protocol:      protocol,               // protocol it should listen on (in net.Conn form)
+		Address:       addr,                   // address to listen on
+		DefaultExport: "default",              // name of default export
+		Exports:       []nbd.ExportConfig{ec}, // array of configurations of exported items
+		//TLS:             nbd.TLSConfig{},        // TLS configuration
+		DisableNoZeroes: false,     // Disable NoZereos extension FIXME
+		Debug:           dump != 0, // Verbose debug
+	}
+	s.wg.Add(1)
+	go func() {
+		defer s.wg.Done()
+		// FIXME contexts
+		nbd.StartServer(ctx, ctx, &s.sessionWaitGroup, logger, serverConfig)
+	}()
+
+	return s, nil
+}
+
+// Wait for the server to finish
+func (s *NBD) Wait() {
+	s.wg.Wait()
+	_ = s.logWr.Close()
+	_ = s.logRd.Close()
+}

cmd/serve/nbd/nbd.md

@@ -0,0 +1,139 @@
+Run a Network Block Device server using remote:path to store the object.
+
+You can use a unix socket by setting the url to `unix:/path/to/socket`
+or just by using an absolute path name.
+
+`rclone serve nbd` will run on any OS, but the examples for using it
+are Linux specific. There do exist Windows and macOS NBD clients but
+these haven't been tested yet.
+
+To see the packets on the wire use `--dump headers` or `--dump bodies`.
+
+**NB** this has no authentication. It may in the future allow SSL
+certificates. If you need access control then you will have to provide
+it on the network layer, or use unix sockets.
+
+### remote:path pointing to a file
+
+If the `remote:path` points to a file then rclone will serve the file
+directly as a network block device.
+
+Using this with `--read-only` is recommended. You can use any
+`--vfs-cache-mode` and only parts of the file that are read will be
+cached locally if using `--vfs-cache-mode full`.
+
+If you don't use `--read-only` then `--vfs-cache-mode full` is
+required and the entire file will be cached locally and won't be
+uploaded until the client has disconnected (`nbd-client -d`).
+
+### remote:path pointing to a directory
+
+If the `remote:path` points to a directory then rclone will treat the
+directory as a place to store chunks of the exported network block device.
+
+It will store an `info.json` file in the top level and store the
+individual chunks in a hierarchical directory scheme with no more than
+256 chunks or directories in any directory.
+
+The first time you use this, you should use the `--create` flag
+indicating how big you want the network block device to appear. Rclone
+only allocates space you use so you can make this large. For example
+`--create 1T`. You can also pass the `--chunk-size` flag at this
+point. If you don't you will get the default of 64k chunks.
+
+Rclone will then chunk the network block device into `--chunk-size`
+chunks. Rclone has to download the entire chunk in order to change
+only part of it and it will cache the chunk on disk so bear that in
+mind when choosing `--chunk-size`.
+
+If you wish to change the size of the network block device you can use
+the `--resize` flag. This won't remove any data, it just changes the
+size advertised. So if you have made a file system on the block device
+you will need to resize it too.
+
+If you are using `--read-only` then you can use any
+`--vfs-cache-mode`.
+
+If you are not using `--read-only` then you will need
+`--vfs-cache-mode writes` or `--vfs-cache-mode full`.
+
+Note that rclone will be acting as a writeback cache with
+`--vfs-cache-mode writes` or `--vfs-cache-mode full`. Note that rclone
+will only write `--transfers` files at once so the cache can get a
+backlog of uploads. You can reduce the writeback caching slightly
+setting `--vfs-write-back 0`, however due to the way the kernel works,
+this will only reduce it slightly.
+
+If using `--vfs-cache-mode writes` or `--vfs-cache-mode full` it is
+recommended to set limits on the cache size using some or all of these
+flags as the VFS can use a lot of disk space very quickly.
+
+    --vfs-cache-max-age duration           Max time since last access of objects in the cache (default 1h0m0s)
+    --vfs-cache-max-size SizeSuffix        Max total size of objects in the cache (default off)
+    --vfs-cache-min-free-space SizeSuffix  Target minimum free space on the disk containing the cache (default off)
+
+You might also need to set this smaller as the cache will only be
+examined at this interval.
+
+    --vfs-cache-poll-interval duration     Interval to poll the cache for stale objects (default 1m0s)
+
+### Linux Examples
+
+Install
+
+    sudo apt install nbd-client
+
+Start server on localhost:10809 by default.
+
+    rclone -v --vfs-cache-mode full serve ndb remote:path
+
+List devices
+
+    sudo modprobe nbd
+    sudo nbd-client --list localhost
+
+Format the partition and mount read write
+
+    sudo nbd-client -g localhost 10809 /dev/nbd0
+    sudo mkfs.ext4 /dev/nbd0
+    sudo mkdir -p /mnt/tmp
+    sudo mount -t ext4 /dev/nbd0 /mnt/tmp
+
+Mount read only
+
+    rclone -v --vfs-cache-mode full --read-only serve ndb remote:path
+    sudo nbd-client --readonly -g localhost 10809 /dev/nbd0
+    sudo mount -t ext4 -o ro /dev/nbd0 /mnt/tmp
+
+Disconnect
+
+    sudo umount /mnt/tmp
+    sudo nbd-client -d /dev/nbd0
+
+### TODO
+
+Experiment with `-connections` option. This is supported by the code.
+Does it improve performance?
+
+       -connections num
+
+       -C     Use  num connections to the server, to allow speeding up request
+              handling, at the cost of higher resource usage  on  the  server.
+              Use  of this option requires kernel support available first with
+              Linux 4.9.
+
+Experiment with `-persist` option - is that a good idea?
+
+       -persist
+
+       -p     When  this  option is specified, nbd-client will immediately try
+              to reconnect an nbd device if the connection  ever  drops  unex‐
+              pectedly due to a lost server or something similar.
+
+Need to implement Trim and see if Trim is being called.
+
+Need to delete zero files before upload (do in VFS layer?)
+
+FIXME need better back pressure from VFS cache to writers.
+
+FIXME need Sync to actually work!

cmd/serve/serve.go

@@ -9,6 +9,7 @@ import (
 	"github.com/rclone/rclone/cmd/serve/docker"
 	"github.com/rclone/rclone/cmd/serve/ftp"
 	"github.com/rclone/rclone/cmd/serve/http"
+	"github.com/rclone/rclone/cmd/serve/nbd"
 	"github.com/rclone/rclone/cmd/serve/nfs"
 	"github.com/rclone/rclone/cmd/serve/restic"
 	"github.com/rclone/rclone/cmd/serve/s3"
@@ -43,6 +44,9 @@ func init() {
 	if s3.Command != nil {
 		Command.AddCommand(s3.Command)
 	}
+	if nbd.Command != nil {
+		Command.AddCommand(nbd.Command)
+	}
 	cmd.Root.AddCommand(Command)
 }
 

go.mod

@@ -2,6 +2,8 @@ module github.com/rclone/rclone
 
 go 1.21
 
+//replace github.com/rclone/gonbdserver => /home/ncw/go/src/github.com/rclone/gonbdserver
+
 require (
 	bazil.org/fuse v0.0.0-20230120002735-62a210ff1fd5
 	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.13.0
@@ -53,6 +55,7 @@ require (
 	github.com/prometheus/client_golang v1.19.1
 	github.com/putdotio/go-putio/putio v0.0.0-20200123120452-16d982cac2b8
 	github.com/rclone/gofakes3 v0.0.3-0.20240716093803-d6abc178be56
+	github.com/rclone/gonbdserver v0.0.0-20230928185136-7adb4642e1cb
 	github.com/rfjakob/eme v1.1.2
 	github.com/rivo/uniseg v0.4.7
 	github.com/rogpeppe/go-internal v1.12.0

go.sum

@@ -460,6 +460,8 @@ github.com/rasky/go-xdr v0.0.0-20170124162913-1a41d1a06c93 h1:UVArwN/wkKjMVhh2EQ
 github.com/rasky/go-xdr v0.0.0-20170124162913-1a41d1a06c93/go.mod h1:Nfe4efndBz4TibWycNE+lqyJZiMX4ycx+QKV8Ta0f/o=
 github.com/rclone/gofakes3 v0.0.3-0.20240716093803-d6abc178be56 h1:JmCt3EsTnlZrg/PHIyZqvKDRvBCde/rmThAQFliE9bU=
 github.com/rclone/gofakes3 v0.0.3-0.20240716093803-d6abc178be56/go.mod h1:L0VIBE0mT6ArN/5dfHsJm3UjqCpi5B/cdN+qWDNh7ko=
+github.com/rclone/gonbdserver v0.0.0-20230928185136-7adb4642e1cb h1:4FyF15nQLPIhLcJDpn2ItwcuO3E/pYQXdPVOt+v3Duk=
+github.com/rclone/gonbdserver v0.0.0-20230928185136-7adb4642e1cb/go.mod h1:HwROhGq4gA7vncM5mLZjoNbI9CrS52aDuHReB3NMWp4=
 github.com/relvacode/iso8601 v1.3.0 h1:HguUjsGpIMh/zsTczGN3DVJFxTU/GX+MMmzcKoMO7ko=
 github.com/relvacode/iso8601 v1.3.0/go.mod h1:FlNp+jz+TXpyRqgmM7tnzHHzBnz776kmAH2h3sZCn0I=
 github.com/rfjakob/eme v1.1.2 h1:SxziR8msSOElPayZNFfQw4Tjx/Sbaeeh3eRvrHVMUs4=