serve nfs: implement on disk cache for file handles

cmd/nfsmount/nfsmount_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/rclone/rclone/vfs/vfscommon"
 	"github.com/rclone/rclone/vfs/vfstest"
+	"github.com/stretchr/testify/require"
 )
 
 // Return true if the command ran without error
@@ -28,5 +29,7 @@ func TestMount(t *testing.T) {
 		}
 		sudo = true
 	}
+	nfsServerOpt.HandleCacheDir = t.TempDir()
+	require.NoError(t, nfsServerOpt.HandleCache.Set("disk"))
 	vfstest.RunTests(t, false, vfscommon.CacheModeWrites, false, mount)
 }

cmd/serve/nfs/cache.go

@@ -3,7 +3,24 @@
 package nfs
 
 import (
+	"crypto/md5"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"math"
+	"os"
+	"path"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+
 	billy "github.com/go-git/go-billy/v5"
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/config"
+	"github.com/rclone/rclone/lib/encoder"
+	"github.com/rclone/rclone/lib/file"
+	"github.com/willscott/go-nfs"
 	nfshelper "github.com/willscott/go-nfs/helpers"
 )
 
@@ -25,8 +42,121 @@ type Cache interface {
 }
 
 // Set the cache of the handler to the type required by the user
-func (h *Handler) setCache() (err error) {
-	// The default caching handler
-	h.Cache = nfshelper.NewCachingHandler(h, h.opt.HandleLimit)
+func (h *Handler) getCache() (c Cache, err error) {
+	switch h.opt.HandleCache {
+	case cacheMemory:
+		return nfshelper.NewCachingHandler(h, h.opt.HandleLimit), nil
+	case cacheDisk:
+		return newDiskHandler(h)
+	case cacheSymlink:
+		if runtime.GOOS != "linux" {
+			return nil, errors.New("can only use symlink cache on Linux")
+		}
+		return nil, errors.New("FIXME not implemented yet")
+	}
+	return nil, errors.New("unknown handle cache type")
+}
+
+// diskHandler implements an on disk NFS file handle cache
+type diskHandler struct {
+	mu       sync.RWMutex
+	cacheDir string
+	billyFS  billy.Filesystem
+}
+
+// Create a new disk handler
+func newDiskHandler(h *Handler) (dh *diskHandler, err error) {
+	cacheDir := h.opt.HandleCacheDir
+	// If cacheDir isn't set then make one from the config
+	if cacheDir == "" {
+		// How the VFS was configured
+		configString := fs.ConfigString(h.vfs.Fs())
+		// Turn it into a valid OS directory name
+		dirName := encoder.OS.ToStandardName(configString)
+		cacheDir = filepath.Join(config.GetCacheDir(), "serve-nfs-handle-cache-"+h.opt.HandleCache.String(), dirName)
+	}
+	// Create the cache dir
+	err = file.MkdirAll(cacheDir, 0700)
+	if err != nil {
+		return nil, fmt.Errorf("disk handler mkdir failed: %v", err)
+	}
+	dh = &diskHandler{
+		cacheDir: cacheDir,
+		billyFS:  h.billyFS,
+	}
+	fs.Infof("nfs", "Storing handle cache in %q", dh.cacheDir)
+	return dh, nil
+}
+
+// Convert a path to a hash
+func hashPath(fullPath string) []byte {
+	hash := md5.Sum([]byte(fullPath))
+	return hash[:]
+}
+
+// Convert a handle to a path on disk for the handle
+func (dh *diskHandler) handleToPath(fh []byte) (cachePath string) {
+	fhString := hex.EncodeToString(fh)
+	if len(fhString) <= 4 {
+		cachePath = filepath.Join(dh.cacheDir, fhString)
+	} else {
+		cachePath = filepath.Join(dh.cacheDir, fhString[0:2], fhString[2:4], fhString)
+	}
+	return cachePath
+}
+
+// ToHandle takes a file and represents it with an opaque handle to reference it.
+// In stateless nfs (when it's serving a unix fs) this can be the device + inode
+// but we can generalize with a stateful local cache of handed out IDs.
+func (dh *diskHandler) ToHandle(f billy.Filesystem, splitPath []string) (fh []byte) {
+	dh.mu.Lock()
+	defer dh.mu.Unlock()
+	fullPath := path.Join(splitPath...)
+	fh = hashPath(fullPath)
+	cachePath := dh.handleToPath(fh)
+	cacheDir := filepath.Dir(cachePath)
+	err := os.MkdirAll(cacheDir, 0700)
+	if err != nil {
+		fs.Errorf("nfs", "Couldn't create cache file handle directory: %v", err)
+		return fh
+	}
+	err = os.WriteFile(cachePath, []byte(fullPath), 0600)
+	if err != nil {
+		fs.Errorf("nfs", "Couldn't create cache file handle: %v", err)
+		return fh
+	}
+	return fh
+}
+
+var errStaleHandle = &nfs.NFSStatusError{NFSStatus: nfs.NFSStatusStale}
+
+// FromHandle converts from an opaque handle to the file it represents
+func (dh *diskHandler) FromHandle(fh []byte) (f billy.Filesystem, splitPath []string, err error) {
+	dh.mu.RLock()
+	defer dh.mu.RUnlock()
+	cachePath := dh.handleToPath(fh)
+	fullPathBytes, err := os.ReadFile(cachePath)
+	if err != nil {
+		fs.Errorf("nfs", "Stale handle %q: %v", cachePath, err)
+		return nil, nil, errStaleHandle
+	}
+	splitPath = strings.Split(string(fullPathBytes), "/")
+	return dh.billyFS, splitPath, nil
+}
+
+// Invalidate the handle passed - used on rename and delete
+func (dh *diskHandler) InvalidateHandle(f billy.Filesystem, fh []byte) error {
+	dh.mu.Lock()
+	defer dh.mu.Unlock()
+	cachePath := dh.handleToPath(fh)
+	err := os.Remove(cachePath)
+	if err != nil {
+		fs.Errorf("nfs", "Failed to remove handle %q: %v", cachePath, err)
+	}
 	return nil
 }
+
+// HandleLimit exports how many file handles can be safely stored by this cache.
+func (dh *diskHandler) HandleLimit() int {
+	return math.MaxInt
+}

cmd/serve/nfs/cache_test.go

@@ -0,0 +1,134 @@
+//go:build unix
+
+package nfs
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"testing"
+
+	"github.com/rclone/rclone/fs"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Check basic CRUD operations
+func testCacheCRUD(t *testing.T, h *Handler, c Cache, fileName string) {
+	// Check reading a non existent handle returns an error
+	_, _, err := c.FromHandle([]byte{10})
+	assert.Error(t, err)
+
+	// Write a handle
+	splitPath := []string{"dir", fileName}
+	fh := c.ToHandle(h.billyFS, splitPath)
+	assert.True(t, len(fh) > 0)
+
+	// Read the handle back
+	newFs, newSplitPath, err := c.FromHandle(fh)
+	require.NoError(t, err)
+	assert.Equal(t, h.billyFS, newFs)
+	assert.Equal(t, splitPath, newSplitPath)
+
+	// Invalidate the handle
+	err = c.InvalidateHandle(h.billyFS, fh)
+	require.NoError(t, err)
+
+	// Invalidate the handle twice
+	err = c.InvalidateHandle(h.billyFS, fh)
+	require.NoError(t, err)
+
+	// Check the handle is gone and returning stale handle error
+	_, _, err = c.FromHandle(fh)
+	require.Error(t, err)
+	assert.Equal(t, errStaleHandle, err)
+}
+
+// Thrash the cache operations in parallel on different files
+func testCacheThrashDifferent(t *testing.T, h *Handler, c Cache) {
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		i := i
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			testCacheCRUD(t, h, c, fmt.Sprintf("file-%d", i))
+		}()
+	}
+	wg.Wait()
+}
+
+// Thrash the cache operations in parallel on the same file
+func testCacheThrashSame(t *testing.T, h *Handler, c Cache) {
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			// Write a handle
+			splitPath := []string{"file"}
+			fh := c.ToHandle(h.billyFS, splitPath)
+			assert.True(t, len(fh) > 0)
+
+			// Read the handle back
+			newFs, newSplitPath, err := c.FromHandle(fh)
+			if err != nil {
+				assert.Equal(t, errStaleHandle, err)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, h.billyFS, newFs)
+				assert.Equal(t, splitPath, newSplitPath)
+			}
+
+			// Invalidate the handle
+			err = c.InvalidateHandle(h.billyFS, fh)
+			require.NoError(t, err)
+
+			// Check the handle is gone and returning stale handle error
+			_, _, err = c.FromHandle(fh)
+			if err != nil {
+				require.Error(t, err)
+				assert.Equal(t, errStaleHandle, err)
+			}
+		}()
+	}
+	wg.Wait()
+}
+
+func TestCache(t *testing.T) {
+	// Quieten the flood of ERROR messages!
+	ci := fs.GetConfig(context.Background())
+	oldLogLevel := ci.LogLevel
+	ci.LogLevel = fs.LogLevelEmergency
+	defer func() {
+		ci.LogLevel = oldLogLevel
+	}()
+	billyFS := &FS{nil} // place holder billyFS
+	for _, cacheType := range []handleCache{cacheMemory, cacheDisk} {
+		cacheType := cacheType
+		t.Run(cacheType.String(), func(t *testing.T) {
+			h := &Handler{
+				billyFS: billyFS,
+			}
+			h.opt.HandleLimit = 1000
+			h.opt.HandleCache = cacheType
+			h.opt.HandleCacheDir = t.TempDir()
+			c, err := h.getCache()
+			require.NoError(t, err)
+
+			t.Run("CRUD", func(t *testing.T) {
+				testCacheCRUD(t, h, c, "file")
+			})
+			// NB the default caching handler is not thread safe!
+			if cacheType != cacheMemory {
+				t.Run("ThrashDifferent", func(t *testing.T) {
+					testCacheThrashDifferent(t, h, c)
+				})
+				t.Run("ThrashSame", func(t *testing.T) {
+					testCacheThrashSame(t, h, c)
+				})
+			}
+		})
+	}
+}

cmd/serve/nfs/handler.go

@@ -13,32 +13,30 @@ import (
 	"github.com/rclone/rclone/fs/log"
 	"github.com/rclone/rclone/vfs"
 	"github.com/willscott/go-nfs"
-	nfshelper "github.com/willscott/go-nfs/helpers"
 )
 
 // Handler returns a NFS backing that exposes a given file system in response to all mount requests.
 type Handler struct {
 	vfs     *vfs.VFS
-	opt     *Options
+	opt     Options
 	billyFS *FS
 	Cache
 }
 
 // NewHandler creates a handler for the provided filesystem
-func NewHandler(vfs *vfs.VFS, opt *Options) (nfs.Handler, error) {
-	handler := &Handler{
+func NewHandler(vfs *vfs.VFS, opt *Options) (handler nfs.Handler, err error) {
+	h := &Handler{
 		vfs:     vfs,
-		opt:     opt,
+		opt:     *opt,
 		billyFS: &FS{vfs: vfs},
 	}
-	handler.opt.HandleLimit = handler.opt.Limit()
-	err := handler.setCache()
+	h.opt.HandleLimit = h.opt.Limit()
+	h.Cache, err = h.getCache()
 	if err != nil {
 		return nil, fmt.Errorf("failed to make cache: %w", err)
 	}
-	handler.Cache = nfshelper.NewCachingHandler(handler, handler.opt.HandleLimit)
 	nfs.SetLogger(&logIntercepter{Level: nfs.DebugLevel})
-	return handler, nil
+	return h, nil
 }
 
 // Mount backs Mount RPC Requests, allowing for access control policies.
@@ -83,7 +81,7 @@ func (h *Handler) HandleLimit() int {
 	return h.Cache.HandleLimit()
 }
 
-// Invalidate the handle passed - used on rename and delete
+// InvalidateHandle invalidates the handle passed - used on rename and delete
 func (h *Handler) InvalidateHandle(f billy.Filesystem, b []byte) (err error) {
 	defer log.Trace("nfs", "handle=%X", b)("err=%v", &err)
 	return h.Cache.InvalidateHandle(f, b)

cmd/serve/nfs/nfs.go

@@ -1,16 +1,17 @@
 //go:build unix
 
-// Package nfs implements a server to serve a VFS remote over NFSv3 protocol
+// Package nfs implements a server to serve a VFS remote over the NFSv3 protocol
 //
-// There is no authentication available on this server
-// and it is served on loopback interface by default.
+// There is no authentication available on this server and it is
+// served on the loopback interface by default.
 //
-// This is primarily used for mounting a VFS remote
-// in macOS, where FUSE-mounting mechanisms are usually not available.
+// This is primarily used for mounting a VFS remote in macOS, where
+// FUSE-mounting mechanisms are usually not available.
 package nfs
 
 import (
 	"context"
+	"strings"
 
 	"github.com/rclone/rclone/cmd"
 	"github.com/rclone/rclone/fs"
@@ -31,16 +32,44 @@ var OptionsInfo = fs.Options{{
 	Name:    "nfs_cache_handle_limit",
 	Default: 1000000,
 	Help:    "max file handles cached simultaneously (min 5)",
+}, {
+	Name:    "nfs_cache_type",
+	Default: cacheMemory,
+	Help:    "Type of NFS handle cache to use",
+}, {
+	Name:    "nfs_cache_dir",
+	Default: "",
+	Help:    "The directory the NFS handle cache will use if set",
 }}
 
 func init() {
 	fs.RegisterGlobalOptions(fs.OptionsInfo{Name: "nfs", Opt: &opt, Options: OptionsInfo})
 }
 
+type handleCache = fs.Enum[handleCacheChoices]
+
+const (
+	cacheMemory handleCache = iota
+	cacheDisk
+	cacheSymlink
+)
+
+type handleCacheChoices struct{}
+
+func (handleCacheChoices) Choices() []string {
+	return []string{
+		cacheMemory:  "memory",
+		cacheDisk:    "disk",
+		cacheSymlink: "symlink",
+	}
+}
+
 // Options contains options for the NFS Server
 type Options struct {
 	ListenAddr     string      `config:"addr"`                   // Port to listen on
 	HandleLimit    int         `config:"nfs_cache_handle_limit"` // max file handles cached by go-nfs CachingHandler
+	HandleCache    handleCache `config:"nfs_cache_type"`         // what kind of handle cache to use
+	HandleCacheDir string      `config:"nfs_cache_dir"`          // where the handle cache should be stored
 }
 
 var opt Options
@@ -73,38 +102,73 @@ func Run(command *cobra.Command, args []string) {
 var Command = &cobra.Command{
 	Use:   "nfs remote:path",
 	Short: `Serve the remote as an NFS mount`,
-	Long: `Create an NFS server that serves the given remote over the network.
+	Long: strings.ReplaceAll(`Create an NFS server that serves the given remote over the network.
 	
-The primary purpose for this command is to enable [mount command](/commands/rclone_mount/) on recent macOS versions where
+This implements an NFSv3 server to serve any rclone remote via NFS.
+
+The primary purpose for this command is to enable the [mount
+command](/commands/rclone_mount/) on recent macOS versions where
 installing FUSE is very cumbersome.
 
-Since this is running on NFSv3, no authentication method is available. Any client
-will be able to access the data. To limit access, you can use serve NFS on loopback address
-and rely on secure tunnels (such as SSH). For this reason, by default, a random TCP port is chosen and loopback interface is used for the listening address;
-meaning that it is only available to the local machine. If you want other machines to access the
-NFS mount over local network, you need to specify the listening address and port using ` + "`--addr`" + ` flag.
+This server does not implement any authentication so any client will be
+able to access the data. To limit access, you can use |serve nfs| on
+the loopback address or rely on secure tunnels (such as SSH) or use
+firewalling.
 
-Modifying files through NFS protocol requires VFS caching. Usually you will need to specify ` + "`--vfs-cache-mode`" + `
-in order to be able to write to the mountpoint (full is recommended). If you don't specify VFS cache mode,
-the mount will be read-only. Note also that ` + "`--nfs-cache-handle-limit`" + ` controls the maximum number of cached file handles stored by the caching handler.
-This should not be set too low or you may experience errors when trying to access files. The default is ` + "`1000000`" + `, but consider lowering this limit if
-the server's system resource usage causes problems.
+For this reason, by default, a random TCP port is chosen and the
+loopback interface is used for the listening address by default;
+meaning that it is only available to the local machine. If you want
+other machines to access the NFS mount over local network, you need to
+specify the listening address and port using the |--addr| flag.
+
+Modifying files through the NFS protocol requires VFS caching. Usually
+you will need to specify |--vfs-cache-mode| in order to be able to
+write to the mountpoint (|full| is recommended). If you don't specify
+VFS cache mode, the mount will be read-only.
+
+|--nfs-cache-type| controls the type of the NFS handle cache. By
+default this is |memory| where new handles will be randomly allocated
+when needed. These are stored in memory. If the server is restarted
+the handle cache will be lost and connected NFS clients will get stale
+handle errors.
+
+|--nfs-cache-type disk| uses an on disk NFS handle cache. Rclone
+hashes the path of the object and stores it in a file named after the
+hash. These hashes are stored on disk the directory controlled by
+|--cache-dir| or the exact directory may be specified with
+|--nfs-cache-dir|. Using this means that the NFS server can be
+restarted at will without affecting the connected clients.
+
+|--nfs-cache-type symlink| is similar to |--nfs-cache-type disk| in
+that it uses an on disk cache, but the cache entries are held as
+symlinks. Rclone will use the handle of the underlying file as the NFS
+handle which improves performance. This sort of cache can't be backed
+up and restored as the underlying handles will change. This is Linux
+only.
+
+|--nfs-cache-handle-limit| controls the maximum number of cached NFS
+handles stored by the caching handler. This should not be set too low
+or you may experience errors when trying to access files. The default
+is |1000000|, but consider lowering this limit if the server's system
+resource usage causes problems. This is only used by the |memory| type
+cache.
 
 To serve NFS over the network use following command:
 
     rclone serve nfs remote: --addr 0.0.0.0:$PORT --vfs-cache-mode=full
 
-We specify a specific port that we can use in the mount command:
-
-To mount the server under Linux/macOS, use the following command:
+This specifies a port that can be used in the mount command. To mount
+the server under Linux/macOS, use the following command:
     
     mount -t nfs -o port=$PORT,mountport=$PORT,tcp $HOSTNAME:/ path/to/mountpoint
 
-Where ` + "`$PORT`" + ` is the same port number we used in the serve nfs command.
+Where |$PORT| is the same port number used in the |serve nfs| command
+and |$HOSTNAME| is the network address of the machine that |serve nfs|
+was run on.
 
-This feature is only available on Unix platforms.
+This command is only available on Unix platforms.
 
-` + vfs.Help(),
+`, "|", "`") + vfs.Help(),
 	Annotations: map[string]string{
 		"versionIntroduced": "v1.65",
 		"groups":            "Filter",