fs: add initial dirfd caching

dirfd caching was temporarily removed when moving
to the v2api. Add it back to gain back some lost speed.

3 files changed, 43 insertions, 13 deletions

diff --git a/internal/fusefrontend/dircache.go b/internal/fusefrontend/dircache.go
index d6ec52c..f8932d8 100644
--- a/internal/fusefrontend/dircache.go
+++ b/internal/fusefrontend/dircache.go
@@ -21,13 +21,11 @@ const (
 	enableDebugMessages = false
 	// Enable hit rate statistics printing
 	enableStats = false
-
-	pathFmt = "%-40q"
 )
 
 type dirCacheEntryStruct struct {
-	// relative plaintext path to the directory
-	dirRelPath string
+	// pointer to the Node this entry belongs to
+	node *Node
 	// fd to the directory (opened with O_PATH!)
 	fd int
 	// content of gocryptfs.diriv in this directory
@@ -46,7 +44,7 @@ func (e *dirCacheEntryStruct) Clear() {
 		}
 	}
 	e.fd = -1
-	e.dirRelPath = ""
+	e.node = nil
 	e.iv = nil
 }
 
@@ -76,7 +74,7 @@ func (d *dirCacheStruct) Clear() {
 
 // Store the entry in the cache. The passed "fd" will be Dup()ed, and the caller
 // can close their copy at will.
-func (d *dirCacheStruct) Store(dirRelPath string, fd int, iv []byte) {
+func (d *dirCacheStruct) Store(node *Node, fd int, iv []byte) {
 	// Note: package ensurefds012, imported from main, guarantees that dirCache
 	// can never get fds 0,1,2.
 	if fd <= 0 || len(iv) != nametransform.DirIVLen {
@@ -94,9 +92,9 @@ func (d *dirCacheStruct) Store(dirRelPath string, fd int, iv []byte) {
 		tlog.Warn.Printf("dirCache.Store: Dup failed: %v", err)
 		return
 	}
-	d.dbg("Store  "+pathFmt+" fd=%d iv=%x\n", dirRelPath, fd2, iv)
+	d.dbg("dirCache.Store  %p fd=%d iv=%x\n", node, fd2, iv)
 	e.fd = fd2
-	e.dirRelPath = dirRelPath
+	e.node = node
 	e.iv = iv
 	// expireThread is started on the first Lookup()
 	if !d.expireThreadRunning {
@@ -108,7 +106,7 @@ func (d *dirCacheStruct) Store(dirRelPath string, fd int, iv []byte) {
 // Lookup checks if relPath is in the cache, and returns an (fd, iv) pair.
 // It returns (-1, nil) if not found. The fd is internally Dup()ed and the
 // caller must close it when done.
-func (d *dirCacheStruct) Lookup(dirRelPath string) (fd int, iv []byte) {
+func (d *dirCacheStruct) Lookup(node *Node) (fd int, iv []byte) {
 	d.Lock()
 	defer d.Unlock()
 	if enableStats {
@@ -121,7 +119,7 @@ func (d *dirCacheStruct) Lookup(dirRelPath string) (fd int, iv []byte) {
 			// Cache slot is empty
 			continue
 		}
-		if dirRelPath != e.dirRelPath {
+		if node != e.node {
 			// Not the right path
 			continue
 		}
@@ -135,7 +133,7 @@ func (d *dirCacheStruct) Lookup(dirRelPath string) (fd int, iv []byte) {
 		break
 	}
 	if fd == 0 {
-		d.dbg("Lookup "+pathFmt+" miss\n", dirRelPath)
+		d.dbg("dirCache.Lookup %p miss\n", node)
 		return -1, nil
 	}
 	if enableStats {
@@ -144,7 +142,7 @@ func (d *dirCacheStruct) Lookup(dirRelPath string) (fd int, iv []byte) {
 	if fd <= 0 || len(iv) != nametransform.DirIVLen {
 		log.Panicf("Lookup sanity check failed: fd=%d len=%d", fd, len(iv))
 	}
-	d.dbg("Lookup "+pathFmt+" hit fd=%d dup=%d iv=%x\n", dirRelPath, e.fd, fd, iv)
+	d.dbg("dirCache.Lookup %p hit fd=%d dup=%d iv=%x\n", node, e.fd, fd, iv)
 	return fd, iv
 }
 
diff --git a/internal/fusefrontend/node_helpers.go b/internal/fusefrontend/node_helpers.go
index a8d1ebe..c44a559 100644
--- a/internal/fusefrontend/node_helpers.go
+++ b/internal/fusefrontend/node_helpers.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/hanwen/go-fuse/v2/fuse"
 
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
@@ -83,11 +84,28 @@ func (n *Node) rootNode() *RootNode {
 // a child of this node.
 // If `child` is empty, the (dirfd, cName) pair refers to this node itself.
 func (n *Node) prepareAtSyscall(child string) (dirfd int, cName string, errno syscall.Errno) {
+	rn := n.rootNode()
+
+	// Cache lookup
+	// TODO: also handle caching for root node & plaintextnames
+	cacheable := (child != "" && !rn.args.PlaintextNames)
+	if cacheable {
+		var iv []byte
+		dirfd, iv = rn.dirCache.Lookup(n)
+		if dirfd > 0 {
+			cName, err := rn.nameTransform.EncryptAndHashName(child, iv)
+			if err != nil {
+				return -1, "", fs.ToErrno(err)
+			}
+			return dirfd, cName, 0
+		}
+	}
+
+	// Slowpath
 	p := n.Path()
 	if child != "" {
 		p = filepath.Join(p, child)
 	}
-	rn := n.rootNode()
 	if rn.isFiltered(p) {
 		errno = syscall.EPERM
 		return
@@ -96,6 +114,18 @@ func (n *Node) prepareAtSyscall(child string) (dirfd int, cName string, errno sy
 	if err != nil {
 		errno = fs.ToErrno(err)
 	}
+
+	// Cache store
+	// TODO: also handle caching for root node & plaintextnames
+	if cacheable {
+		// TODO: openBackingDir already calls ReadDirIVAt(). Get the data out.
+		iv, err := nametransform.ReadDirIVAt(dirfd)
+		if err != nil {
+			syscall.Close(dirfd)
+			return -1, "", fs.ToErrno(err)
+		}
+		rn.dirCache.Store(n, dirfd, iv)
+	}
 	return
 }
 
diff --git a/internal/fusefrontend/root_node.go b/internal/fusefrontend/root_node.go
index bdefafa..cdac4d4 100644
--- a/internal/fusefrontend/root_node.go
+++ b/internal/fusefrontend/root_node.go
@@ -48,6 +48,8 @@ type RootNode struct {
 	// When -idle was used when mounting, idleMonitor() sets it to 1
 	// periodically.
 	IsIdle uint32
+	// dirCache caches directory fds
+	dirCache dirCacheStruct
 	// inoMap translates inode numbers from different devices to unique inode
 	// numbers.
 	inoMap inomap.TranslateStater