5 files changed, 1158 insertions, 26 deletions

diff --git a/runsc/fsgofer/BUILD b/runsc/fsgofer/BUILD
index c6967cc57..8d5a6d300 100644
--- a/runsc/fsgofer/BUILD
+++ b/runsc/fsgofer/BUILD
@@ -13,10 +13,12 @@ go_library(
     ],
     visibility = ["//runsc:__subpackages__"],
     deps = [
+        "//pkg/abi/linux",
         "//pkg/cleanup",
         "//pkg/fd",
         "//pkg/lisafs",
         "//pkg/log",
+        "//pkg/marshal/primitive",
         "//pkg/p9",
         "//pkg/sync",
         "//pkg/syserr",
@@ -39,3 +41,15 @@ go_test(
         "@org_golang_x_sys//unix:go_default_library",
     ],
 )
+
+go_test(
+    name = "lisafs_test",
+    size = "small",
+    srcs = ["lisafs_test.go"],
+    deps = [
+        ":fsgofer",
+        "//pkg/lisafs",
+        "//pkg/lisafs/testsuite",
+        "//pkg/log",
+    ],
+)
diff --git a/runsc/fsgofer/fsgofer_test.go b/runsc/fsgofer/fsgofer_test.go
index ee6cc97df..6cdd6d695 100644
--- a/runsc/fsgofer/fsgofer_test.go
+++ b/runsc/fsgofer/fsgofer_test.go
@@ -105,14 +105,14 @@ func testReadWrite(f p9.File, flags p9.OpenFlags, content []byte) error {
 	return nil
 }
 
-type state struct {
+type fileState struct {
 	root     *localFile
 	file     *localFile
 	conf     Config
 	fileType uint32
 }
 
-func (s state) String() string {
+func (s fileState) String() string {
 	return fmt.Sprintf("type(%v)", s.fileType)
 }
 
@@ -129,11 +129,11 @@ func typeName(fileType uint32) string {
 	}
 }
 
-func runAll(t *testing.T, test func(*testing.T, state)) {
+func runAll(t *testing.T, test func(*testing.T, fileState)) {
 	runCustom(t, allTypes, allConfs, test)
 }
 
-func runCustom(t *testing.T, types []uint32, confs []Config, test func(*testing.T, state)) {
+func runCustom(t *testing.T, types []uint32, confs []Config, test func(*testing.T, fileState)) {
 	for _, c := range confs {
 		for _, ft := range types {
 			name := fmt.Sprintf("%s/%s", configTestName(&c), typeName(ft))
@@ -159,7 +159,7 @@ func runCustom(t *testing.T, types []uint32, confs []Config, test func(*testing.
 					t.Fatalf("root.Walk({%q}) failed, err: %v", "symlink", err)
 				}
 
-				st := state{
+				st := fileState{
 					root:     root.(*localFile),
 					file:     file.(*localFile),
 					conf:     c,
@@ -227,7 +227,7 @@ func createFile(dir *localFile, name string) (*localFile, error) {
 }
 
 func TestReadWrite(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		child, err := createFile(s.file, "test")
 		if err != nil {
 			t.Fatalf("%v: createFile() failed, err: %v", s, err)
@@ -261,7 +261,7 @@ func TestReadWrite(t *testing.T) {
 }
 
 func TestCreate(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		for i, flags := range allOpenFlags {
 			_, l, _, _, err := s.file.Create(fmt.Sprintf("test-%d", i), flags, 0777, p9.UID(os.Getuid()), p9.GID(os.Getgid()))
 			if err != nil {
@@ -296,7 +296,7 @@ func TestCreateSetGID(t *testing.T) {
 		t.Skipf("Test requires CAP_CHOWN")
 	}
 
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		// Change group and set setgid to the parent dir.
 		if err := unix.Chown(s.file.hostPath, os.Getuid(), nobody); err != nil {
 			t.Fatalf("Chown() failed: %v", err)
@@ -364,7 +364,7 @@ func TestCreateSetGID(t *testing.T) {
 // TestReadWriteDup tests that a file opened in any mode can be dup'ed and
 // reopened in any other mode.
 func TestReadWriteDup(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		child, err := createFile(s.file, "test")
 		if err != nil {
 			t.Fatalf("%v: createFile() failed, err: %v", s, err)
@@ -410,7 +410,7 @@ func TestReadWriteDup(t *testing.T) {
 }
 
 func TestUnopened(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFREG}, allConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFREG}, allConfs, func(t *testing.T, s fileState) {
 		b := []byte("foobar")
 		if _, err := s.file.WriteAt(b, 0); err != unix.EBADF {
 			t.Errorf("%v: WriteAt() should have failed, got: %v, expected: unix.EBADF", s, err)
@@ -432,7 +432,7 @@ func TestUnopened(t *testing.T) {
 // was open with O_PATH, but Open() was not checking for it and allowing the
 // control file to be reused.
 func TestOpenOPath(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFREG}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFREG}, rwConfs, func(t *testing.T, s fileState) {
 		// Fist remove all permissions on the file.
 		if err := s.file.SetAttr(p9.SetAttrMask{Permissions: true}, p9.SetAttr{Permissions: p9.FileMode(0)}); err != nil {
 			t.Fatalf("SetAttr(): %v", err)
@@ -465,7 +465,7 @@ func SetGetAttr(l *localFile, valid p9.SetAttrMask, attr p9.SetAttr) (p9.Attr, e
 }
 
 func TestSetAttrPerm(t *testing.T) {
-	runCustom(t, allTypes, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, rwConfs, func(t *testing.T, s fileState) {
 		valid := p9.SetAttrMask{Permissions: true}
 		attr := p9.SetAttr{Permissions: 0777}
 		got, err := SetGetAttr(s.file, valid, attr)
@@ -485,7 +485,7 @@ func TestSetAttrPerm(t *testing.T) {
 }
 
 func TestSetAttrSize(t *testing.T) {
-	runCustom(t, allTypes, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, rwConfs, func(t *testing.T, s fileState) {
 		for _, size := range []uint64{1024, 0, 1024 * 1024} {
 			valid := p9.SetAttrMask{Size: true}
 			attr := p9.SetAttr{Size: size}
@@ -508,7 +508,7 @@ func TestSetAttrSize(t *testing.T) {
 }
 
 func TestSetAttrTime(t *testing.T) {
-	runCustom(t, allTypes, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, rwConfs, func(t *testing.T, s fileState) {
 		valid := p9.SetAttrMask{ATime: true, ATimeNotSystemTime: true}
 		attr := p9.SetAttr{ATimeSeconds: 123, ATimeNanoSeconds: 456}
 		got, err := SetGetAttr(s.file, valid, attr)
@@ -542,7 +542,7 @@ func TestSetAttrOwner(t *testing.T) {
 		t.Skipf("SetAttr(owner) test requires CAP_CHOWN, running as %d", os.Getuid())
 	}
 
-	runCustom(t, allTypes, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, rwConfs, func(t *testing.T, s fileState) {
 		newUID := os.Getuid() + 1
 		valid := p9.SetAttrMask{UID: true}
 		attr := p9.SetAttr{UID: p9.UID(newUID)}
@@ -571,7 +571,7 @@ func SetGetXattr(l *localFile, name string, value string) error {
 }
 
 func TestSetGetDisabledXattr(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFREG}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFREG}, rwConfs, func(t *testing.T, s fileState) {
 		name := "user.merkle.offset"
 		value := "tmp"
 		err := SetGetXattr(s.file, name, value)
@@ -582,7 +582,7 @@ func TestSetGetDisabledXattr(t *testing.T) {
 }
 
 func TestSetGetXattr(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFREG}, []Config{{ROMount: false, EnableVerityXattr: true}}, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFREG}, []Config{{ROMount: false, EnableVerityXattr: true}}, func(t *testing.T, s fileState) {
 		name := "user.merkle.offset"
 		value := "tmp"
 		err := SetGetXattr(s.file, name, value)
@@ -596,7 +596,7 @@ func TestLink(t *testing.T) {
 	if !specutils.HasCapabilities(capability.CAP_DAC_READ_SEARCH) {
 		t.Skipf("Link test requires CAP_DAC_READ_SEARCH, running as %d", os.Getuid())
 	}
-	runCustom(t, allTypes, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, rwConfs, func(t *testing.T, s fileState) {
 		const dirName = "linkdir"
 		const linkFile = "link"
 		if _, err := s.root.Mkdir(dirName, 0777, p9.UID(os.Getuid()), p9.GID(os.Getgid())); err != nil {
@@ -625,7 +625,7 @@ func TestROMountChecks(t *testing.T) {
 	uid := p9.UID(os.Getuid())
 	gid := p9.GID(os.Getgid())
 
-	runCustom(t, allTypes, roConfs, func(t *testing.T, s state) {
+	runCustom(t, allTypes, roConfs, func(t *testing.T, s fileState) {
 		if s.fileType != unix.S_IFLNK {
 			if _, _, _, err := s.file.Open(p9.WriteOnly); err != want {
 				t.Errorf("Open() should have failed, got: %v, expected: %v", err, want)
@@ -676,7 +676,7 @@ func TestROMountChecks(t *testing.T) {
 }
 
 func TestWalkNotFound(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, allConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, allConfs, func(t *testing.T, s fileState) {
 		if _, _, err := s.file.Walk([]string{"nobody-here"}); err != unix.ENOENT {
 			t.Errorf("Walk(%q) should have failed, got: %v, expected: unix.ENOENT", "nobody-here", err)
 		}
@@ -695,7 +695,7 @@ func TestWalkNotFound(t *testing.T) {
 }
 
 func TestWalkDup(t *testing.T) {
-	runAll(t, func(t *testing.T, s state) {
+	runAll(t, func(t *testing.T, s fileState) {
 		_, dup, err := s.file.Walk([]string{})
 		if err != nil {
 			t.Fatalf("%v: Walk(nil) failed, err: %v", s, err)
@@ -708,7 +708,7 @@ func TestWalkDup(t *testing.T) {
 }
 
 func TestWalkMultiple(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		var names []string
 		var parent p9.File = s.file
 		for i := 0; i < 5; i++ {
@@ -729,7 +729,7 @@ func TestWalkMultiple(t *testing.T) {
 }
 
 func TestReaddir(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		name := "dir"
 		if _, err := s.file.Mkdir(name, 0777, p9.UID(os.Getuid()), p9.GID(os.Getgid())); err != nil {
 			t.Fatalf("%v: MkDir(%s) failed, err: %v", s, name, err)
@@ -915,7 +915,7 @@ func TestDoubleAttachError(t *testing.T) {
 }
 
 func TestTruncate(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		child, err := createFile(s.file, "test")
 		if err != nil {
 			t.Fatalf("createFile() failed: %v", err)
@@ -951,7 +951,7 @@ func TestTruncate(t *testing.T) {
 }
 
 func TestMknod(t *testing.T) {
-	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s state) {
+	runCustom(t, []uint32{unix.S_IFDIR}, rwConfs, func(t *testing.T, s fileState) {
 		_, err := s.file.Mknod("test", p9.ModeRegular|0777, 1, 2, p9.UID(os.Getuid()), p9.GID(os.Getgid()))
 		if err != nil {
 			t.Fatalf("Mknod() failed: %v", err)
diff --git a/runsc/fsgofer/fsgofer_unsafe.go b/runsc/fsgofer/fsgofer_unsafe.go
index f11fea40d..fb4fbe0d2 100644
--- a/runsc/fsgofer/fsgofer_unsafe.go
+++ b/runsc/fsgofer/fsgofer_unsafe.go
@@ -21,6 +21,8 @@ import (
 	"gvisor.dev/gvisor/pkg/syserr"
 )
 
+var unixDirentMaxSize uint32 = uint32(unsafe.Sizeof(unix.Dirent{}))
+
 func utimensat(dirFd int, name string, times [2]unix.Timespec, flags int) error {
 	// utimensat(2) doesn't accept empty name, instead name must be nil to make it
 	// operate directly on 'dirFd' unlike other *at syscalls.
@@ -80,3 +82,31 @@ func renameat(oldDirFD int, oldName string, newDirFD int, newName string) error
 	}
 	return nil
 }
+
+func parseDirents(buf []byte, handleDirent func(ino uint64, off int64, ftype uint8, name string) bool) {
+	for len(buf) > 0 {
+		// Interpret the buf populated by unix.Getdents as unix.Dirent.
+		dirent := *(*unix.Dirent)(unsafe.Pointer(&buf[0]))
+
+		// Extracting the name is pretty tedious...
+		var nameBuf [unix.NAME_MAX]byte
+		var nameLen int
+		for i := 0; i < len(dirent.Name); i++ {
+			// The name is null terminated.
+			if dirent.Name[i] == 0 {
+				nameLen = i
+				break
+			}
+			nameBuf[i] = byte(dirent.Name[i])
+		}
+		name := string(nameBuf[:nameLen])
+
+		// Deliver results to caller.
+		if !handleDirent(dirent.Ino, dirent.Off, dirent.Type, name) {
+			return
+		}
+
+		// Advance buf for the next dirent.
+		buf = buf[dirent.Reclen:]
+	}
+}
diff --git a/runsc/fsgofer/lisafs.go b/runsc/fsgofer/lisafs.go
index 9d745f461..0db44ff6a 100644
--- a/runsc/fsgofer/lisafs.go
+++ b/runsc/fsgofer/lisafs.go
@@ -15,7 +15,20 @@
 package fsgofer
 
 import (
+	"io"
+	"math"
+	"path"
+	"strconv"
+	"sync/atomic"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/cleanup"
+	rwfd "gvisor.dev/gvisor/pkg/fd"
 	"gvisor.dev/gvisor/pkg/lisafs"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/marshal/primitive"
+	"gvisor.dev/gvisor/pkg/p9"
 )
 
 // LisafsServer implements lisafs.ServerImpl for fsgofer.
@@ -35,7 +48,19 @@ func NewLisafsServer(config Config) *LisafsServer {
 
 // Mount implements lisafs.ServerImpl.Mount.
 func (s *LisafsServer) Mount(c *lisafs.Connection, mountPath string) (lisafs.ControlFDImpl, lisafs.Inode, error) {
-	panic("unimplemented")
+	s.RenameMu.RLock()
+	defer s.RenameMu.RUnlock()
+
+	rootFD, rootStat, err := tryStepLocked(c, mountPath, nil, func(flags int) (int, error) {
+		return unix.Open(mountPath, flags, 0)
+	})
+	if err != nil {
+		return nil, lisafs.Inode{}, err
+	}
+
+	var rootIno lisafs.Inode
+	rootFD.initInodeWithStat(&rootIno, &rootStat)
+	return rootFD, rootIno, nil
 }
 
 // MaxMessageSize implements lisafs.ServerImpl.MaxMessageSize.
@@ -45,8 +70,1015 @@ func (s *LisafsServer) MaxMessageSize() uint32 {
 
 // SupportedMessages implements lisafs.ServerImpl.SupportedMessages.
 func (s *LisafsServer) SupportedMessages() []lisafs.MID {
+	// Note that Flush, FListXattr and FRemoveXattr are not supported.
 	return []lisafs.MID{
 		lisafs.Mount,
 		lisafs.Channel,
+		lisafs.FStat,
+		lisafs.SetStat,
+		lisafs.Walk,
+		lisafs.WalkStat,
+		lisafs.OpenAt,
+		lisafs.OpenCreateAt,
+		lisafs.Close,
+		lisafs.FSync,
+		lisafs.PWrite,
+		lisafs.PRead,
+		lisafs.MkdirAt,
+		lisafs.MknodAt,
+		lisafs.SymlinkAt,
+		lisafs.LinkAt,
+		lisafs.FStatFS,
+		lisafs.FAllocate,
+		lisafs.ReadLinkAt,
+		lisafs.Connect,
+		lisafs.UnlinkAt,
+		lisafs.RenameAt,
+		lisafs.Getdents64,
+		lisafs.FGetXattr,
+		lisafs.FSetXattr,
+	}
+}
+
+// controlFDLisa implements lisafs.ControlFDImpl.
+type controlFDLisa struct {
+	lisafs.ControlFD
+
+	// hostFD is the file descriptor which can be used to make host syscalls.
+	hostFD int
+
+	// writableHostFD is the file descriptor number for a writable FD opened on the
+	// same FD as `hostFD`. writableHostFD must only be accessed using atomic
+	// operations. It is initialized to -1, and can change in value exactly once.
+	writableHostFD int32
+}
+
+var _ lisafs.ControlFDImpl = (*controlFDLisa)(nil)
+
+// Precondition: server's rename mutex must be at least read locked.
+func newControlFDLisaLocked(c *lisafs.Connection, hostFD int, parent *controlFDLisa, name string, mode linux.FileMode) *controlFDLisa {
+	fd := &controlFDLisa{
+		hostFD:         hostFD,
+		writableHostFD: -1,
+	}
+	fd.ControlFD.Init(c, parent.FD(), name, mode, fd)
+	return fd
+}
+
+func (fd *controlFDLisa) initInode(inode *lisafs.Inode) error {
+	inode.ControlFD = fd.ID()
+	return fstatTo(fd.hostFD, &inode.Stat)
+}
+
+func (fd *controlFDLisa) initInodeWithStat(inode *lisafs.Inode, unixStat *unix.Stat_t) {
+	inode.ControlFD = fd.ID()
+	unixToLinuxStat(unixStat, &inode.Stat)
+}
+
+func (fd *controlFDLisa) getWritableFD() (int, error) {
+	if writableFD := atomic.LoadInt32(&fd.writableHostFD); writableFD != -1 {
+		return int(writableFD), nil
+	}
+
+	writableFD, err := unix.Openat(int(procSelfFD.FD()), strconv.Itoa(fd.hostFD), (unix.O_WRONLY|openFlags)&^unix.O_NOFOLLOW, 0)
+	if err != nil {
+		return -1, err
+	}
+	if !atomic.CompareAndSwapInt32(&fd.writableHostFD, -1, int32(writableFD)) {
+		// Race detected, use the new value and clean this up.
+		unix.Close(writableFD)
+		return int(atomic.LoadInt32(&fd.writableHostFD)), nil
+	}
+	return writableFD, nil
+}
+
+// FD implements lisafs.ControlFDImpl.FD.
+func (fd *controlFDLisa) FD() *lisafs.ControlFD {
+	if fd == nil {
+		return nil
+	}
+	return &fd.ControlFD
+}
+
+// Close implements lisafs.ControlFDImpl.Close.
+func (fd *controlFDLisa) Close(c *lisafs.Connection) {
+	if fd.hostFD >= 0 {
+		_ = unix.Close(fd.hostFD)
+		fd.hostFD = -1
+	}
+	// No concurrent access is possible so no need to use atomics.
+	if fd.writableHostFD >= 0 {
+		_ = unix.Close(int(fd.writableHostFD))
+		fd.writableHostFD = -1
+	}
+}
+
+// Stat implements lisafs.ControlFDImpl.Stat.
+func (fd *controlFDLisa) Stat(c *lisafs.Connection, comm lisafs.Communicator) (uint32, error) {
+	var resp linux.Statx
+	if err := fstatTo(fd.hostFD, &resp); err != nil {
+		return 0, err
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// SetStat implements lisafs.ControlFDImpl.SetStat.
+func (fd *controlFDLisa) SetStat(c *lisafs.Connection, comm lisafs.Communicator, stat lisafs.SetStatReq) (uint32, error) {
+	var resp lisafs.SetStatResp
+	if stat.Mask&unix.STATX_MODE != 0 {
+		if err := unix.Fchmod(fd.hostFD, stat.Mode&^unix.S_IFMT); err != nil {
+			log.Debugf("SetStat fchmod failed %q, err: %v", fd.FilePath(), err)
+			resp.FailureMask |= unix.STATX_MODE
+			resp.FailureErrNo = uint32(p9.ExtractErrno(err))
+		}
+	}
+
+	if stat.Mask&unix.STATX_SIZE != 0 {
+		// ftruncate(2) requires the FD to be open for writing.
+		writableFD, err := fd.getWritableFD()
+		if err == nil {
+			err = unix.Ftruncate(writableFD, int64(stat.Size))
+		}
+		if err != nil {
+			log.Debugf("SetStat ftruncate failed %q, err: %v", fd.FilePath(), err)
+			resp.FailureMask |= unix.STATX_SIZE
+			resp.FailureErrNo = uint32(p9.ExtractErrno(err))
+		}
+	}
+
+	if stat.Mask&(unix.STATX_ATIME|unix.STATX_MTIME) != 0 {
+		utimes := [2]unix.Timespec{
+			{Sec: 0, Nsec: unix.UTIME_OMIT},
+			{Sec: 0, Nsec: unix.UTIME_OMIT},
+		}
+		if stat.Mask&unix.STATX_ATIME != 0 {
+			utimes[0].Sec = stat.Atime.Sec
+			utimes[0].Nsec = stat.Atime.Nsec
+		}
+		if stat.Mask&unix.STATX_MTIME != 0 {
+			utimes[1].Sec = stat.Mtime.Sec
+			utimes[1].Nsec = stat.Mtime.Nsec
+		}
+
+		if fd.IsSymlink() {
+			// utimensat operates different that other syscalls. To operate on a
+			// symlink it *requires* AT_SYMLINK_NOFOLLOW with dirFD and a non-empty
+			// name.
+			c.Server().WithRenameReadLock(func() error {
+				if err := utimensat(fd.ParentLocked().(*controlFDLisa).hostFD, fd.NameLocked(), utimes, unix.AT_SYMLINK_NOFOLLOW); err != nil {
+					log.Debugf("SetStat utimens failed %q, err: %v", fd.FilePathLocked(), err)
+					resp.FailureMask |= (stat.Mask & (unix.STATX_ATIME | unix.STATX_MTIME))
+					resp.FailureErrNo = uint32(p9.ExtractErrno(err))
+				}
+				return nil
+			})
+		} else {
+			hostFD := fd.hostFD
+			if fd.IsRegular() {
+				// For regular files, utimensat(2) requires the FD to be open for
+				// writing, see BUGS section.
+				writableFD, err := fd.getWritableFD()
+				if err != nil {
+					return 0, err
+				}
+				hostFD = writableFD
+			}
+			// Directories and regular files can operate directly on the fd
+			// using empty name.
+			err := utimensat(hostFD, "", utimes, 0)
+			if err != nil {
+				log.Debugf("SetStat utimens failed %q, err: %v", fd.FilePath(), err)
+				resp.FailureMask |= (stat.Mask & (unix.STATX_ATIME | unix.STATX_MTIME))
+				resp.FailureErrNo = uint32(p9.ExtractErrno(err))
+			}
+		}
+	}
+
+	if stat.Mask&(unix.STATX_UID|unix.STATX_GID) != 0 {
+		// "If the owner or group is specified as -1, then that ID is not changed"
+		// - chown(2)
+		uid := -1
+		if stat.Mask&unix.STATX_UID != 0 {
+			uid = int(stat.UID)
+		}
+		gid := -1
+		if stat.Mask&unix.STATX_GID != 0 {
+			gid = int(stat.GID)
+		}
+		if err := unix.Fchownat(fd.hostFD, "", uid, gid, unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW); err != nil {
+			log.Debugf("SetStat fchown failed %q, err: %v", fd.FilePath(), err)
+			resp.FailureMask |= stat.Mask & (unix.STATX_UID | unix.STATX_GID)
+			resp.FailureErrNo = uint32(p9.ExtractErrno(err))
+		}
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Walk implements lisafs.ControlFDImpl.Walk.
+func (fd *controlFDLisa) Walk(c *lisafs.Connection, comm lisafs.Communicator, path lisafs.StringArray) (uint32, error) {
+	// We need to generate inodes for each component walked. We will manually
+	// marshal the inodes into the payload buffer as they are generated to avoid
+	// the slice allocation. The memory format should be lisafs.WalkResp's.
+	var numInodes primitive.Uint32
+	var status lisafs.WalkStatus
+	maxPayloadSize := status.SizeBytes() + numInodes.SizeBytes() + (len(path) * (*lisafs.Inode)(nil).SizeBytes())
+	if maxPayloadSize > math.MaxUint32 {
+		// Too much to walk, can't do.
+		return 0, unix.EIO
+	}
+	payloadBuf := comm.PayloadBuf(uint32(maxPayloadSize))
+	payloadPos := status.SizeBytes() + numInodes.SizeBytes()
+
+	s := c.Server()
+	s.RenameMu.RLock()
+	defer s.RenameMu.RUnlock()
+
+	curDirFD := fd
+	cu := cleanup.Make(func() {
+		// Destroy all newly created FDs until now. Walk upward from curDirFD to
+		// fd. Do not destroy fd as the client still owns that.
+		for curDirFD != fd {
+			c.RemoveControlFDLocked(curDirFD.ID())
+			curDirFD = curDirFD.ParentLocked().(*controlFDLisa)
+		}
+	})
+	defer cu.Clean()
+
+	for _, name := range path {
+		// Symlinks terminate walk. This client gets the symlink inode, but will
+		// have to invoke Walk again with the resolved path.
+		if curDirFD.IsSymlink() {
+			status = lisafs.WalkComponentSymlink
+			break
+		}
+
+		child, childStat, err := tryStepLocked(c, name, curDirFD, func(flags int) (int, error) {
+			return unix.Openat(curDirFD.hostFD, name, flags, 0)
+		})
+		if err == unix.ENOENT {
+			status = lisafs.WalkComponentDoesNotExist
+			break
+		}
+		if err != nil {
+			return 0, err
+		}
+
+		// Write inode to payloadBuf and update state.
+		var childInode lisafs.Inode
+		child.initInodeWithStat(&childInode, &childStat)
+		childInode.MarshalUnsafe(payloadBuf[payloadPos:])
+		payloadPos += childInode.SizeBytes()
+		numInodes++
+		curDirFD = child
+	}
+	cu.Release()
+
+	// lisafs.WalkResp writes the walk status followed by the number of inodes in
+	// the beginning.
+	status.MarshalUnsafe(payloadBuf)
+	numInodes.MarshalUnsafe(payloadBuf[status.SizeBytes():])
+	return uint32(payloadPos), nil
+}
+
+// WalkStat implements lisafs.ControlFDImpl.WalkStat.
+func (fd *controlFDLisa) WalkStat(c *lisafs.Connection, comm lisafs.Communicator, path lisafs.StringArray) (uint32, error) {
+	// We may need to generate statx for dirFD + each component walked. We will
+	// manually marshal the statx results into the payload buffer as they are
+	// generated to avoid the slice allocation. The memory format should be the
+	// same as lisafs.WalkStatResp's.
+	var numStats primitive.Uint32
+	maxPayloadSize := numStats.SizeBytes() + (len(path) * linux.SizeOfStatx)
+	if maxPayloadSize > math.MaxUint32 {
+		// Too much to walk, can't do.
+		return 0, unix.EIO
+	}
+	payloadBuf := comm.PayloadBuf(uint32(maxPayloadSize))
+	payloadPos := numStats.SizeBytes()
+
+	s := c.Server()
+	s.RenameMu.RLock()
+	defer s.RenameMu.RUnlock()
+
+	curDirFD := fd.hostFD
+	closeCurDirFD := func() {
+		if curDirFD != fd.hostFD {
+			unix.Close(curDirFD)
+		}
+	}
+	defer closeCurDirFD()
+	var (
+		stat     linux.Statx
+		unixStat unix.Stat_t
+	)
+	if len(path) > 0 && len(path[0]) == 0 {
+		// Write stat results for dirFD if the first path component is "".
+		if err := unix.Fstat(fd.hostFD, &unixStat); err != nil {
+			return 0, err
+		}
+		unixToLinuxStat(&unixStat, &stat)
+		stat.MarshalUnsafe(payloadBuf[payloadPos:])
+		payloadPos += stat.SizeBytes()
+		path = path[1:]
+		numStats++
+	}
+
+	// Don't attempt walking if parent is a symlink.
+	if fd.IsSymlink() {
+		return 0, nil
+	}
+	for _, name := range path {
+		curFD, err := unix.Openat(curDirFD, name, unix.O_PATH|openFlags, 0)
+		if err == unix.ENOENT {
+			// No more path components exist on the filesystem. Return the partial
+			// walk to the client.
+			break
+		}
+		if err != nil {
+			return 0, err
+		}
+		closeCurDirFD()
+		curDirFD = curFD
+
+		// Write stat results for curFD.
+		if err := unix.Fstat(curFD, &unixStat); err != nil {
+			return 0, err
+		}
+		unixToLinuxStat(&unixStat, &stat)
+		stat.MarshalUnsafe(payloadBuf[payloadPos:])
+		payloadPos += stat.SizeBytes()
+		numStats++
+
+		// Symlinks terminate walk. This client gets the symlink stat result, but
+		// will have to invoke Walk again with the resolved path.
+		if unixStat.Mode&unix.S_IFMT == unix.S_IFLNK {
+			break
+		}
+	}
+
+	// lisafs.WalkStatResp writes the number of stats in the beginning.
+	numStats.MarshalUnsafe(payloadBuf)
+	return uint32(payloadPos), nil
+}
+
+// Open implements lisafs.ControlFDImpl.Open.
+func (fd *controlFDLisa) Open(c *lisafs.Connection, comm lisafs.Communicator, flags uint32) (uint32, error) {
+	flags |= openFlags
+	newHostFD, err := unix.Openat(int(procSelfFD.FD()), strconv.Itoa(fd.hostFD), int(flags)&^unix.O_NOFOLLOW, 0)
+	if err != nil {
+		return 0, err
+	}
+	newFD := fd.newOpenFDLisa(newHostFD, flags)
+
+	if fd.IsRegular() {
+		// Donate FD for regular files only. Since FD donation is a destructive
+		// operation, we should duplicate the to-be-donated FD. Eat the error if
+		// one occurs, it is better to have an FD without a host FD, than failing
+		// the Open attempt.
+		if dupFD, err := unix.Dup(newFD.hostFD); err == nil {
+			_ = comm.DonateFD(dupFD)
+		}
+	}
+
+	resp := lisafs.OpenAtResp{NewFD: newFD.ID()}
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// OpenCreate implements lisafs.ControlFDImpl.OpenCreate.
+func (fd *controlFDLisa) OpenCreate(c *lisafs.Connection, comm lisafs.Communicator, mode linux.FileMode, uid lisafs.UID, gid lisafs.GID, name string, flags uint32) (uint32, error) {
+	// Need to hold rename mutex for reading while performing the walk. Also keep
+	// holding it while the cleanup is still possible.
+	var resp lisafs.OpenCreateAtResp
+	var newFD *openFDLisa
+	if err := c.Server().WithRenameReadLock(func() error {
+		createFlags := unix.O_CREAT | unix.O_EXCL | unix.O_RDONLY | unix.O_NONBLOCK | openFlags
+		childHostFD, err := unix.Openat(fd.hostFD, name, createFlags, uint32(mode&^linux.FileTypeMask))
+		if err != nil {
+			return err
+		}
+
+		childFD := newControlFDLisaLocked(c, childHostFD, fd, name, linux.ModeRegular)
+		cu := cleanup.Make(func() {
+			// Best effort attempt to remove the file in case of failure.
+			if err := unix.Unlinkat(fd.hostFD, name, 0); err != nil {
+				log.Warningf("error unlinking file %q after failure: %v", path.Join(fd.FilePathLocked(), name), err)
+			}
+			c.RemoveControlFDLocked(childFD.ID())
+		})
+		defer cu.Clean()
+
+		// Set the owners as requested by the client.
+		if err := unix.Fchownat(childFD.hostFD, "", int(uid), int(gid), unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW); err != nil {
+			log.Infof("ayush: Fchownat %v", err)
+			return err
+		}
+
+		// Do not use the stat result from tryOpen because the owners might have
+		// changed. initInode() will stat the FD again and use fresh results.
+		if err := childFD.initInode(&resp.Child); err != nil {
+			log.Infof("ayush: initInode %v", err)
+			return err
+		}
+
+		// Now open an FD to the newly created file with the flags requested by the client.
+		flags |= openFlags
+		newHostFD, err := unix.Openat(int(procSelfFD.FD()), strconv.Itoa(childFD.hostFD), int(flags)&^unix.O_NOFOLLOW, 0)
+		if err != nil {
+			log.Infof("ayush: Openat %v", err)
+			return err
+		}
+		cu.Release()
+
+		newFD = childFD.newOpenFDLisa(newHostFD, uint32(flags))
+		resp.NewFD = newFD.ID()
+		return nil
+	}); err != nil {
+		return 0, err
+	}
+
+	// Donate FD because open(O_CREAT|O_EXCL) always creates a regular file.
+	// Since FD donation is a destructive operation, we should duplicate the
+	// to-be-donated FD. Eat the error if one occurs, it is better to have an FD
+	// without a host FD, than failing the Open attempt.
+	if dupFD, err := unix.Dup(newFD.hostFD); err == nil {
+		_ = comm.DonateFD(dupFD)
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Mkdir implements lisafs.ControlFDImpl.Mkdir.
+func (fd *controlFDLisa) Mkdir(c *lisafs.Connection, comm lisafs.Communicator, mode linux.FileMode, uid lisafs.UID, gid lisafs.GID, name string) (uint32, error) {
+	var resp lisafs.MkdirAtResp
+	if err := c.Server().WithRenameReadLock(func() error {
+		if err := unix.Mkdirat(fd.hostFD, name, uint32(mode&^linux.FileTypeMask)); err != nil {
+			return err
+		}
+		cu := cleanup.Make(func() {
+			// Best effort attempt to remove the dir in case of failure.
+			if err := unix.Unlinkat(fd.hostFD, name, unix.AT_REMOVEDIR); err != nil {
+				log.Warningf("error unlinking dir %q after failure: %v", path.Join(fd.FilePathLocked(), name), err)
+			}
+		})
+		defer cu.Clean()
+
+		// Open directory to change ownership.
+		childDirFd, err := unix.Openat(fd.hostFD, name, unix.O_DIRECTORY|unix.O_RDONLY|openFlags, 0)
+		if err != nil {
+			return err
+		}
+		if err := unix.Fchownat(childDirFd, "", int(uid), int(gid), unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW); err != nil {
+			unix.Close(childDirFd)
+			return err
+		}
+
+		childDir := newControlFDLisaLocked(c, childDirFd, fd, name, linux.ModeDirectory)
+		if err := childDir.initInode(&resp.ChildDir); err != nil {
+			c.RemoveControlFDLocked(childDir.ID())
+			return err
+		}
+		cu.Release()
+
+		return nil
+	}); err != nil {
+		return 0, err
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Mknod implements lisafs.ControlFDImpl.Mknod.
+func (fd *controlFDLisa) Mknod(c *lisafs.Connection, comm lisafs.Communicator, mode linux.FileMode, uid lisafs.UID, gid lisafs.GID, name string, minor uint32, major uint32) (uint32, error) {
+	// From mknod(2) man page:
+	// "EPERM: [...] if the filesystem containing pathname does not support
+	// the type of node requested."
+	if mode.FileType() != linux.ModeRegular {
+		return 0, unix.EPERM
+	}
+
+	var resp lisafs.MknodAtResp
+	if err := c.Server().WithRenameReadLock(func() error {
+		if err := unix.Mknodat(fd.hostFD, name, uint32(mode), 0); err != nil {
+			return err
+		}
+		cu := cleanup.Make(func() {
+			// Best effort attempt to remove the file in case of failure.
+			if err := unix.Unlinkat(fd.hostFD, name, 0); err != nil {
+				log.Warningf("error unlinking file %q after failure: %v", path.Join(fd.FilePathLocked(), name), err)
+			}
+		})
+		defer cu.Clean()
+
+		// Open file to change ownership.
+		childFD, err := unix.Openat(fd.hostFD, name, unix.O_PATH|openFlags, 0)
+		if err != nil {
+			return err
+		}
+		if err := unix.Fchownat(childFD, "", int(uid), int(gid), unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW); err != nil {
+			unix.Close(childFD)
+			return err
+		}
+
+		child := newControlFDLisaLocked(c, childFD, fd, name, mode)
+		if err := child.initInode(&resp.Child); err != nil {
+			c.RemoveControlFDLocked(child.ID())
+			return err
+		}
+		cu.Release()
+		return nil
+	}); err != nil {
+		return 0, err
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Symlink implements lisafs.ControlFDImpl.Symlink.
+func (fd *controlFDLisa) Symlink(c *lisafs.Connection, comm lisafs.Communicator, name string, target string, uid lisafs.UID, gid lisafs.GID) (uint32, error) {
+	var resp lisafs.SymlinkAtResp
+	if err := c.Server().WithRenameReadLock(func() error {
+		if err := unix.Symlinkat(target, fd.hostFD, name); err != nil {
+			return err
+		}
+		cu := cleanup.Make(func() {
+			// Best effort attempt to remove the symlink in case of failure.
+			if err := unix.Unlinkat(fd.hostFD, name, 0); err != nil {
+				log.Warningf("error unlinking file %q after failure: %v", path.Join(fd.FilePathLocked(), name), err)
+			}
+		})
+		defer cu.Clean()
+
+		// Open symlink to change ownership.
+		symlinkFD, err := unix.Openat(fd.hostFD, name, unix.O_PATH|openFlags, 0)
+		if err != nil {
+			return err
+		}
+		if err := unix.Fchownat(symlinkFD, "", int(uid), int(gid), unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW); err != nil {
+			unix.Close(symlinkFD)
+			return err
+		}
+
+		symlink := newControlFDLisaLocked(c, symlinkFD, fd, name, linux.ModeSymlink)
+		if err := symlink.initInode(&resp.Symlink); err != nil {
+			c.RemoveControlFDLocked(symlink.ID())
+			return err
+		}
+		cu.Release()
+		return nil
+	}); err != nil {
+		return 0, err
 	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Link implements lisafs.ControlFDImpl.Link.
+func (fd *controlFDLisa) Link(c *lisafs.Connection, comm lisafs.Communicator, dir lisafs.ControlFDImpl, name string) (uint32, error) {
+	var resp lisafs.LinkAtResp
+	if err := c.Server().WithRenameReadLock(func() error {
+		dirFD := dir.(*controlFDLisa)
+		if err := unix.Linkat(fd.hostFD, "", dirFD.hostFD, name, unix.AT_EMPTY_PATH); err != nil {
+			return err
+		}
+		cu := cleanup.Make(func() {
+			// Best effort attempt to remove the hard link in case of failure.
+			if err := unix.Unlinkat(dirFD.hostFD, name, 0); err != nil {
+				log.Warningf("error unlinking file %q after failure: %v", path.Join(dirFD.FilePathLocked(), name), err)
+			}
+		})
+		defer cu.Clean()
+
+		linkFD, linkStat, err := tryStepLocked(c, name, dirFD, func(flags int) (int, error) {
+			return unix.Openat(dirFD.hostFD, name, flags, 0)
+		})
+		if err != nil {
+			return err
+		}
+		cu.Release()
+
+		linkFD.initInodeWithStat(&resp.Link, &linkStat)
+		return nil
+	}); err != nil {
+		return 0, err
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// StatFS implements lisafs.ControlFDImpl.StatFS.
+func (fd *controlFDLisa) StatFS(c *lisafs.Connection, comm lisafs.Communicator) (uint32, error) {
+	var s unix.Statfs_t
+	if err := unix.Fstatfs(fd.hostFD, &s); err != nil {
+		return 0, err
+	}
+
+	resp := lisafs.StatFS{
+		Type:            uint64(s.Type),
+		BlockSize:       s.Bsize,
+		Blocks:          s.Blocks,
+		BlocksFree:      s.Bfree,
+		BlocksAvailable: s.Bavail,
+		Files:           s.Files,
+		FilesFree:       s.Ffree,
+		NameLength:      uint64(s.Namelen),
+	}
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Readlink implements lisafs.ControlFDImpl.Readlink.
+func (fd *controlFDLisa) Readlink(c *lisafs.Connection, comm lisafs.Communicator) (uint32, error) {
+	// We will manually marshal lisafs.ReadLinkAtResp, which just contains a
+	// lisafs.SizedString. Let unix.Readlinkat directly write into the payload
+	// buffer and manually write the string size before it.
+
+	// This is similar to what os.Readlink does.
+	const limit = primitive.Uint32(1024 * 1024)
+	for linkLen := primitive.Uint32(128); linkLen < limit; linkLen *= 2 {
+		b := comm.PayloadBuf(uint32(linkLen) + uint32(linkLen.SizeBytes()))
+		n, err := unix.Readlinkat(fd.hostFD, "", b[linkLen.SizeBytes():])
+		if err != nil {
+			return 0, err
+		}
+		if n < int(linkLen) {
+			linkLen = primitive.Uint32(n)
+			linkLen.MarshalUnsafe(b[:linkLen.SizeBytes()])
+			return uint32(linkLen) + uint32(linkLen.SizeBytes()), nil
+		}
+	}
+	return 0, unix.ENOMEM
+}
+
+// Connect implements lisafs.ControlFDImpl.Connect.
+func (fd *controlFDLisa) Connect(c *lisafs.Connection, comm lisafs.Communicator, sockType uint32) error {
+	s := c.ServerImpl().(*LisafsServer)
+	if !s.config.HostUDS {
+		return unix.ECONNREFUSED
+	}
+
+	// Lock RenameMu so that the hostPath read stays valid and is not tampered
+	// with until it is actually connected to.
+	s.RenameMu.RLock()
+	defer s.RenameMu.RUnlock()
+
+	// TODO(gvisor.dev/issue/1003): Due to different app vs replacement
+	// mappings, the app path may have fit in the sockaddr, but we can't fit
+	// hostPath in our sockaddr. We'd need to redirect through a shorter path
+	// in order to actually connect to this socket.
+	hostPath := fd.FilePathLocked()
+	if len(hostPath) > 108 { // UNIX_PATH_MAX = 108 is defined in afunix.h.
+		return unix.ECONNREFUSED
+	}
+
+	// Only the following types are supported.
+	switch sockType {
+	case unix.SOCK_STREAM, unix.SOCK_DGRAM, unix.SOCK_SEQPACKET:
+	default:
+		return unix.ENXIO
+	}
+
+	sock, err := unix.Socket(unix.AF_UNIX, int(sockType), 0)
+	if err != nil {
+		return err
+	}
+	if err := comm.DonateFD(sock); err != nil {
+		return err
+	}
+
+	sa := unix.SockaddrUnix{Name: hostPath}
+	if err := unix.Connect(sock, &sa); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Unlink implements lisafs.ControlFDImpl.Unlink.
+func (fd *controlFDLisa) Unlink(c *lisafs.Connection, name string, flags uint32) error {
+	return c.Server().WithRenameReadLock(func() error {
+		return unix.Unlinkat(fd.hostFD, name, int(flags))
+	})
+}
+
+// RenameLocked implements lisafs.ControlFDImpl.RenameLocked.
+func (fd *controlFDLisa) RenameLocked(c *lisafs.Connection, newDir lisafs.ControlFDImpl, newName string) (func(lisafs.ControlFDImpl), func(), error) {
+	// Note that there is no controlFDLisa specific update needed on rename.
+	return nil, nil, renameat(fd.ParentLocked().(*controlFDLisa).hostFD, fd.NameLocked(), newDir.(*controlFDLisa).hostFD, newName)
+}
+
+// GetXattr implements lisafs.ControlFDImpl.GetXattr.
+func (fd *controlFDLisa) GetXattr(c *lisafs.Connection, comm lisafs.Communicator, name string, size uint32) (uint32, error) {
+	if !c.ServerImpl().(*LisafsServer).config.EnableVerityXattr {
+		return 0, unix.EOPNOTSUPP
+	}
+	if _, ok := verityXattrs[name]; !ok {
+		return 0, unix.EOPNOTSUPP
+	}
+
+	// Manually marshal lisafs.FGetXattrResp to avoid allocations and copying.
+	var valueLen primitive.Uint32
+	buf := comm.PayloadBuf(uint32(valueLen.SizeBytes()) + size)
+	n, err := unix.Fgetxattr(fd.hostFD, name, buf[valueLen.SizeBytes():])
+	if err != nil {
+		return 0, err
+	}
+	valueLen = primitive.Uint32(n)
+	valueLen.MarshalBytes(buf[:valueLen.SizeBytes()])
+
+	return uint32(valueLen.SizeBytes() + n), nil
+}
+
+// SetXattr implements lisafs.ControlFDImpl.SetXattr.
+func (fd *controlFDLisa) SetXattr(c *lisafs.Connection, name string, value string, flags uint32) error {
+	if !c.ServerImpl().(*LisafsServer).config.EnableVerityXattr {
+		return unix.EOPNOTSUPP
+	}
+	if _, ok := verityXattrs[name]; !ok {
+		return unix.EOPNOTSUPP
+	}
+	return unix.Fsetxattr(fd.hostFD, name, []byte(value) /* sigh */, int(flags))
+}
+
+// ListXattr implements lisafs.ControlFDImpl.ListXattr.
+func (fd *controlFDLisa) ListXattr(c *lisafs.Connection, comm lisafs.Communicator, size uint64) (uint32, error) {
+	return 0, unix.EOPNOTSUPP
+}
+
+// RemoveXattr implements lisafs.ControlFDImpl.RemoveXattr.
+func (fd *controlFDLisa) RemoveXattr(c *lisafs.Connection, comm lisafs.Communicator, name string) error {
+	return unix.EOPNOTSUPP
+}
+
+// openFDLisa implements lisafs.OpenFDImpl.
+type openFDLisa struct {
+	lisafs.OpenFD
+
+	// hostFD is the host file descriptor which can be used to make syscalls.
+	hostFD int
+}
+
+var _ lisafs.OpenFDImpl = (*openFDLisa)(nil)
+
+func (fd *controlFDLisa) newOpenFDLisa(hostFD int, flags uint32) *openFDLisa {
+	newFD := &openFDLisa{
+		hostFD: hostFD,
+	}
+	newFD.OpenFD.Init(fd.FD(), flags, newFD)
+	return newFD
+}
+
+// FD implements lisafs.OpenFDImpl.FD.
+func (fd *openFDLisa) FD() *lisafs.OpenFD {
+	if fd == nil {
+		return nil
+	}
+	return &fd.OpenFD
+}
+
+// Close implements lisafs.OpenFDImpl.Close.
+func (fd *openFDLisa) Close(c *lisafs.Connection) {
+	if fd.hostFD >= 0 {
+		_ = unix.Close(fd.hostFD)
+		fd.hostFD = -1
+	}
+}
+
+// Stat implements lisafs.OpenFDImpl.Stat.
+func (fd *openFDLisa) Stat(c *lisafs.Connection, comm lisafs.Communicator) (uint32, error) {
+	var resp linux.Statx
+	if err := fstatTo(fd.hostFD, &resp); err != nil {
+		return 0, err
+	}
+
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Sync implements lisafs.OpenFDImpl.Sync.
+func (fd *openFDLisa) Sync(c *lisafs.Connection) error {
+	return unix.Fsync(fd.hostFD)
+}
+
+// Write implements lisafs.OpenFDImpl.Write.
+func (fd *openFDLisa) Write(c *lisafs.Connection, comm lisafs.Communicator, buf []byte, off uint64) (uint32, error) {
+	rw := rwfd.NewReadWriter(fd.hostFD)
+	n, err := rw.WriteAt(buf, int64(off))
+	if err != nil {
+		return 0, err
+	}
+
+	resp := &lisafs.PWriteResp{Count: uint64(n)}
+	respLen := uint32(resp.SizeBytes())
+	resp.MarshalUnsafe(comm.PayloadBuf(respLen))
+	return respLen, nil
+}
+
+// Read implements lisafs.OpenFDImpl.Read.
+func (fd *openFDLisa) Read(c *lisafs.Connection, comm lisafs.Communicator, off uint64, count uint32) (uint32, error) {
+	// To save an allocation and a copy, we directly read into the payload
+	// buffer. The rest of the response message is manually marshalled.
+	var resp lisafs.PReadResp
+	respMetaSize := uint32(resp.NumBytes.SizeBytes())
+	maxRespLen := respMetaSize + count
+
+	payloadBuf := comm.PayloadBuf(maxRespLen)
+	rw := rwfd.NewReadWriter(fd.hostFD)
+	n, err := rw.ReadAt(payloadBuf[respMetaSize:], int64(off))
+	if err != nil && err != io.EOF {
+		return 0, err
+	}
+
+	// Write the response metadata onto the payload buffer. The response contents
+	// already have been written immediately after it.
+	resp.NumBytes = primitive.Uint32(n)
+	resp.NumBytes.MarshalUnsafe(payloadBuf[:respMetaSize])
+	return respMetaSize + uint32(n), nil
+}
+
+// Allocate implements lisafs.OpenFDImpl.Allocate.
+func (fd *openFDLisa) Allocate(c *lisafs.Connection, mode, off, length uint64) error {
+	return unix.Fallocate(fd.hostFD, uint32(mode), int64(off), int64(length))
+}
+
+// Flush implements lisafs.OpenFDImpl.Flush.
+func (fd *openFDLisa) Flush(c *lisafs.Connection) error {
+	return nil
+}
+
+// Getdent64 implements lisafs.OpenFDImpl.Getdent64.
+func (fd *openFDLisa) Getdent64(c *lisafs.Connection, comm lisafs.Communicator, count uint32, seek0 bool) (uint32, error) {
+	if seek0 {
+		if _, err := unix.Seek(fd.hostFD, 0, 0); err != nil {
+			return 0, err
+		}
+	}
+
+	// We will manually marshal the response lisafs.Getdents64Resp.
+
+	// numDirents is the number of dirents marshalled into the payload.
+	var numDirents primitive.Uint32
+	// The payload starts with numDirents, dirents go right after that.
+	// payloadBufPos represents the position at which to write the next dirent.
+	payloadBufPos := uint32(numDirents.SizeBytes())
+	// Request enough payloadBuf for 10 dirents, we will extend when needed.
+	payloadBuf := comm.PayloadBuf(payloadBufPos + 10*unixDirentMaxSize)
+
+	var direntsBuf [8192]byte
+	var bytesRead int
+	for bytesRead < int(count) {
+		bufEnd := len(direntsBuf)
+		if remaining := int(count) - bytesRead; remaining < bufEnd {
+			bufEnd = remaining
+		}
+		n, err := unix.Getdents(fd.hostFD, direntsBuf[:bufEnd])
+		if err != nil {
+			if err == unix.EINVAL && bufEnd < 268 {
+				// getdents64(2) returns EINVAL is returned when the result
+				// buffer is too small. If bufEnd is smaller than the max
+				// size of unix.Dirent, then just break here to return all
+				// dirents collected till now.
+				break
+			}
+			return 0, err
+		}
+		if n <= 0 {
+			break
+		}
+		bytesRead += n
+
+		var statErr error
+		parseDirents(direntsBuf[:n], func(ino uint64, off int64, ftype uint8, name string) bool {
+			dirent := lisafs.Dirent64{
+				Ino:  primitive.Uint64(ino),
+				Off:  primitive.Uint64(off),
+				Type: primitive.Uint8(ftype),
+				Name: lisafs.SizedString(name),
+			}
+
+			// The client also wants the device ID, which annoyingly incurs an
+			// additional syscall per dirent. Live with it.
+			stat, err := statAt(fd.hostFD, name)
+			if err != nil {
+				statErr = err
+				return false
+			}
+			dirent.DevMinor = primitive.Uint32(unix.Minor(stat.Dev))
+			dirent.DevMajor = primitive.Uint32(unix.Major(stat.Dev))
+
+			// Paste the dirent into the payload buffer without having the dirent
+			// escape. Request a larger buffer if needed.
+			if int(payloadBufPos)+dirent.SizeBytes() > len(payloadBuf) {
+				// Ask for 10 large dirents worth of more space.
+				payloadBuf = comm.PayloadBuf(payloadBufPos + 10*unixDirentMaxSize)
+			}
+			dirent.MarshalBytes(payloadBuf[payloadBufPos:])
+			payloadBufPos += uint32(dirent.SizeBytes())
+			numDirents++
+			return true
+		})
+		if statErr != nil {
+			return 0, statErr
+		}
+	}
+
+	// The number of dirents goes at the beginning of the payload.
+	numDirents.MarshalUnsafe(payloadBuf)
+	return payloadBufPos, nil
+}
+
+// tryStepLocked tries to walk via open() with different modes as documented.
+// It then initializes and returns the control FD.
+//
+// Precondition: server's rename mutex must at least be read locked.
+func tryStepLocked(c *lisafs.Connection, name string, parent *controlFDLisa, open func(flags int) (int, error)) (*controlFDLisa, unix.Stat_t, error) {
+	// Attempt to open file in the following in order:
+	//   1. RDONLY | NONBLOCK: for all files, directories, ro mounts, FIFOs.
+	//      Use non-blocking to prevent getting stuck inside open(2) for
+	//      FIFOs. This option has no effect on regular files.
+	//   2. PATH: for symlinks, sockets.
+	options := []struct {
+		flag     int
+		readable bool
+	}{
+		{
+			flag:     unix.O_RDONLY | unix.O_NONBLOCK,
+			readable: true,
+		},
+		{
+			flag:     unix.O_PATH,
+			readable: false,
+		},
+	}
+
+	for i, option := range options {
+		hostFD, err := open(option.flag | openFlags)
+		if err == nil {
+			var stat unix.Stat_t
+			if err = unix.Fstat(hostFD, &stat); err == nil {
+				return newControlFDLisaLocked(c, hostFD, parent, name, linux.FileMode(stat.Mode)), stat, nil
+			}
+			unix.Close(hostFD)
+		}
+
+		e := extractErrno(err)
+		if e == unix.ENOENT {
+			// File doesn't exist, no point in retrying.
+			return nil, unix.Stat_t{}, e
+		}
+		if i < len(options)-1 {
+			continue
+		}
+		return nil, unix.Stat_t{}, e
+	}
+	panic("unreachable")
+}
+
+func fstatTo(hostFD int, stat *linux.Statx) error {
+	var unixStat unix.Stat_t
+	if err := unix.Fstat(hostFD, &unixStat); err != nil {
+		return err
+	}
+
+	unixToLinuxStat(&unixStat, stat)
+	return nil
+}
+
+func unixToLinuxStat(from *unix.Stat_t, to *linux.Statx) {
+	to.Mask = unix.STATX_TYPE | unix.STATX_MODE | unix.STATX_INO | unix.STATX_NLINK | unix.STATX_UID | unix.STATX_GID | unix.STATX_SIZE | unix.STATX_BLOCKS | unix.STATX_ATIME | unix.STATX_MTIME | unix.STATX_CTIME
+	to.Mode = uint16(from.Mode)
+	to.DevMinor = unix.Minor(from.Dev)
+	to.DevMajor = unix.Major(from.Dev)
+	to.Ino = from.Ino
+	to.Nlink = uint32(from.Nlink)
+	to.UID = from.Uid
+	to.GID = from.Gid
+	to.RdevMinor = unix.Minor(from.Rdev)
+	to.RdevMajor = unix.Major(from.Rdev)
+	to.Size = uint64(from.Size)
+	to.Blksize = uint32(from.Blksize)
+	to.Blocks = uint64(from.Blocks)
+	to.Atime.Sec = from.Atim.Sec
+	to.Atime.Nsec = uint32(from.Atim.Nsec)
+	to.Mtime.Sec = from.Mtim.Sec
+	to.Mtime.Nsec = uint32(from.Mtim.Nsec)
+	to.Ctime.Sec = from.Ctim.Sec
+	to.Ctime.Nsec = uint32(from.Ctim.Nsec)
 }
diff --git a/runsc/fsgofer/lisafs_test.go b/runsc/fsgofer/lisafs_test.go
new file mode 100644
index 000000000..4653f9955
--- /dev/null
+++ b/runsc/fsgofer/lisafs_test.go
@@ -0,0 +1,56 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package lisafs_test
+
+import (
+	"testing"
+
+	"gvisor.dev/gvisor/pkg/lisafs"
+	"gvisor.dev/gvisor/pkg/lisafs/testsuite"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/runsc/fsgofer"
+)
+
+// Note that these are not supposed to be extensive or robust tests. These unit
+// tests provide a sanity check that all RPCs at least work in obvious ways.
+
+func init() {
+	log.SetLevel(log.Debug)
+	if err := fsgofer.OpenProcSelfFD(); err != nil {
+		panic(err)
+	}
+}
+
+// tester implements testsuite.Tester.
+type tester struct{}
+
+// NewServer implements testsuite.Tester.NewServer.
+func (tester) NewServer(t *testing.T) *lisafs.Server {
+	return &fsgofer.NewLisafsServer(fsgofer.Config{HostUDS: true, EnableVerityXattr: true}).Server
+}
+
+// LinkSupported implements testsuite.Tester.LinkSupported.
+func (tester) LinkSupported() bool {
+	return true
+}
+
+// SetUserGroupIDSupported implements testsuite.Tester.SetUserGroupIDSupported.
+func (tester) SetUserGroupIDSupported() bool {
+	return true
+}
+
+func TestFSGofer(t *testing.T) {
+	testsuite.RunAllLocalFSTests(t, tester{})
+}