11 files changed, 334 insertions, 400 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/BUILD b/pkg/sentry/fsimpl/kernfs/BUILD
deleted file mode 100644
index ef34cb28a..000000000
--- a/pkg/sentry/fsimpl/kernfs/BUILD
+++ /dev/null
@@ -1,74 +0,0 @@
-load("//tools:defs.bzl", "go_library", "go_test")
-load("//tools/go_generics:defs.bzl", "go_template_instance")
-
-licenses(["notice"])
-
-go_template_instance(
-    name = "fstree",
-    out = "fstree.go",
-    package = "kernfs",
-    prefix = "generic",
-    template = "//pkg/sentry/vfs/genericfstree:generic_fstree",
-    types = {
-        "Dentry": "Dentry",
-    },
-)
-
-go_template_instance(
-    name = "slot_list",
-    out = "slot_list.go",
-    package = "kernfs",
-    prefix = "slot",
-    template = "//pkg/ilist:generic_list",
-    types = {
-        "Element": "*slot",
-        "Linker": "*slot",
-    },
-)
-
-go_library(
-    name = "kernfs",
-    srcs = [
-        "dynamic_bytes_file.go",
-        "fd_impl_util.go",
-        "filesystem.go",
-        "fstree.go",
-        "inode_impl_util.go",
-        "kernfs.go",
-        "slot_list.go",
-        "symlink.go",
-    ],
-    visibility = ["//pkg/sentry:internal"],
-    deps = [
-        "//pkg/abi/linux",
-        "//pkg/context",
-        "//pkg/fspath",
-        "//pkg/log",
-        "//pkg/refs",
-        "//pkg/sentry/kernel/auth",
-        "//pkg/sentry/memmap",
-        "//pkg/sentry/socket/unix/transport",
-        "//pkg/sentry/vfs",
-        "//pkg/sync",
-        "//pkg/syserror",
-        "//pkg/usermem",
-    ],
-)
-
-go_test(
-    name = "kernfs_test",
-    size = "small",
-    srcs = ["kernfs_test.go"],
-    deps = [
-        ":kernfs",
-        "//pkg/abi/linux",
-        "//pkg/context",
-        "//pkg/sentry/contexttest",
-        "//pkg/sentry/fsimpl/testutil",
-        "//pkg/sentry/kernel/auth",
-        "//pkg/sentry/vfs",
-        "//pkg/syserror",
-        "//pkg/usermem",
-        "@com_github_google_go-cmp//cmp:go_default_library",
-    ],
-)
diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index c7779fc11..c7779fc11 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index 8284e76a7..8284e76a7 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 4a12ae245..4a12ae245 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
diff --git a/pkg/sentry/fsimpl/kernfs/fstree.go b/pkg/sentry/fsimpl/kernfs/fstree.go
new file mode 100755
index 000000000..4c4033462
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/fstree.go
@@ -0,0 +1,45 @@
+package kernfs
+
+import (
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+// IsAncestorDentry returns true if d is an ancestor of d2; that is, d is
+// either d2's parent or an ancestor of d2's parent.
+func genericIsAncestorDentry(d, d2 *Dentry) bool {
+	for {
+		if d2.parent == d {
+			return true
+		}
+		if d2.parent == d2 {
+			return false
+		}
+		d2 = d2.parent
+	}
+}
+
+// ParentOrSelf returns d.parent. If d.parent is nil, ParentOrSelf returns d.
+func genericParentOrSelf(d *Dentry) *Dentry {
+	if d.parent != nil {
+		return d.parent
+	}
+	return d
+}
+
+// PrependPath is a generic implementation of FilesystemImpl.PrependPath().
+func genericPrependPath(vfsroot vfs.VirtualDentry, mnt *vfs.Mount, d *Dentry, b *fspath.Builder) error {
+	for {
+		if mnt == vfsroot.Mount() && &d.vfsd == vfsroot.Dentry() {
+			return vfs.PrependPathAtVFSRootError{}
+		}
+		if &d.vfsd == mnt.Root() {
+			return nil
+		}
+		if d.parent == nil {
+			return vfs.PrependPathAtNonMountRootError{}
+		}
+		b.PrependComponent(d.name)
+		d = d.parent
+	}
+}
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 615592d5f..615592d5f 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 732837933..732837933 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
new file mode 100755
index 000000000..299ad87fa
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
@@ -0,0 +1,96 @@
+// automatically generated by stateify.
+
+package kernfs
+
+import (
+	"gvisor.dev/gvisor/pkg/state"
+)
+
+func (x *DynamicBytesFile) beforeSave() {}
+func (x *DynamicBytesFile) save(m state.Map) {
+	x.beforeSave()
+	m.Save("InodeAttrs", &x.InodeAttrs)
+	m.Save("InodeNoopRefCount", &x.InodeNoopRefCount)
+	m.Save("InodeNotDirectory", &x.InodeNotDirectory)
+	m.Save("InodeNotSymlink", &x.InodeNotSymlink)
+	m.Save("data", &x.data)
+}
+
+func (x *DynamicBytesFile) afterLoad() {}
+func (x *DynamicBytesFile) load(m state.Map) {
+	m.Load("InodeAttrs", &x.InodeAttrs)
+	m.Load("InodeNoopRefCount", &x.InodeNoopRefCount)
+	m.Load("InodeNotDirectory", &x.InodeNotDirectory)
+	m.Load("InodeNotSymlink", &x.InodeNotSymlink)
+	m.Load("data", &x.data)
+}
+
+func (x *DynamicBytesFD) beforeSave() {}
+func (x *DynamicBytesFD) save(m state.Map) {
+	x.beforeSave()
+	m.Save("FileDescriptionDefaultImpl", &x.FileDescriptionDefaultImpl)
+	m.Save("DynamicBytesFileDescriptionImpl", &x.DynamicBytesFileDescriptionImpl)
+	m.Save("vfsfd", &x.vfsfd)
+	m.Save("inode", &x.inode)
+}
+
+func (x *DynamicBytesFD) afterLoad() {}
+func (x *DynamicBytesFD) load(m state.Map) {
+	m.Load("FileDescriptionDefaultImpl", &x.FileDescriptionDefaultImpl)
+	m.Load("DynamicBytesFileDescriptionImpl", &x.DynamicBytesFileDescriptionImpl)
+	m.Load("vfsfd", &x.vfsfd)
+	m.Load("inode", &x.inode)
+}
+
+func (x *StaticDirectory) beforeSave() {}
+func (x *StaticDirectory) save(m state.Map) {
+	x.beforeSave()
+	m.Save("InodeNotSymlink", &x.InodeNotSymlink)
+	m.Save("InodeDirectoryNoNewChildren", &x.InodeDirectoryNoNewChildren)
+	m.Save("InodeAttrs", &x.InodeAttrs)
+	m.Save("InodeNoDynamicLookup", &x.InodeNoDynamicLookup)
+	m.Save("OrderedChildren", &x.OrderedChildren)
+}
+
+func (x *StaticDirectory) afterLoad() {}
+func (x *StaticDirectory) load(m state.Map) {
+	m.Load("InodeNotSymlink", &x.InodeNotSymlink)
+	m.Load("InodeDirectoryNoNewChildren", &x.InodeDirectoryNoNewChildren)
+	m.Load("InodeAttrs", &x.InodeAttrs)
+	m.Load("InodeNoDynamicLookup", &x.InodeNoDynamicLookup)
+	m.Load("OrderedChildren", &x.OrderedChildren)
+}
+
+func (x *slotList) beforeSave() {}
+func (x *slotList) save(m state.Map) {
+	x.beforeSave()
+	m.Save("head", &x.head)
+	m.Save("tail", &x.tail)
+}
+
+func (x *slotList) afterLoad() {}
+func (x *slotList) load(m state.Map) {
+	m.Load("head", &x.head)
+	m.Load("tail", &x.tail)
+}
+
+func (x *slotEntry) beforeSave() {}
+func (x *slotEntry) save(m state.Map) {
+	x.beforeSave()
+	m.Save("next", &x.next)
+	m.Save("prev", &x.prev)
+}
+
+func (x *slotEntry) afterLoad() {}
+func (x *slotEntry) load(m state.Map) {
+	m.Load("next", &x.next)
+	m.Load("prev", &x.prev)
+}
+
+func init() {
+	state.Register("pkg/sentry/fsimpl/kernfs.DynamicBytesFile", (*DynamicBytesFile)(nil), state.Fns{Save: (*DynamicBytesFile).save, Load: (*DynamicBytesFile).load})
+	state.Register("pkg/sentry/fsimpl/kernfs.DynamicBytesFD", (*DynamicBytesFD)(nil), state.Fns{Save: (*DynamicBytesFD).save, Load: (*DynamicBytesFD).load})
+	state.Register("pkg/sentry/fsimpl/kernfs.StaticDirectory", (*StaticDirectory)(nil), state.Fns{Save: (*StaticDirectory).save, Load: (*StaticDirectory).load})
+	state.Register("pkg/sentry/fsimpl/kernfs.slotList", (*slotList)(nil), state.Fns{Save: (*slotList).save, Load: (*slotList).load})
+	state.Register("pkg/sentry/fsimpl/kernfs.slotEntry", (*slotEntry)(nil), state.Fns{Save: (*slotEntry).save, Load: (*slotEntry).load})
+}
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_test.go b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
deleted file mode 100644
index a9f671bc8..000000000
--- a/pkg/sentry/fsimpl/kernfs/kernfs_test.go
+++ /dev/null
@@ -1,326 +0,0 @@
-// Copyright 2019 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 kernfs_test
-
-import (
-	"bytes"
-	"fmt"
-	"testing"
-
-	"github.com/google/go-cmp/cmp"
-	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/sentry/contexttest"
-	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
-	"gvisor.dev/gvisor/pkg/sentry/fsimpl/testutil"
-	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
-	"gvisor.dev/gvisor/pkg/sentry/vfs"
-	"gvisor.dev/gvisor/pkg/syserror"
-	"gvisor.dev/gvisor/pkg/usermem"
-)
-
-const defaultMode linux.FileMode = 01777
-const staticFileContent = "This is sample content for a static test file."
-
-// RootDentryFn is a generator function for creating the root dentry of a test
-// filesystem. See newTestSystem.
-type RootDentryFn func(*auth.Credentials, *filesystem) *kernfs.Dentry
-
-// newTestSystem sets up a minimal environment for running a test, including an
-// instance of a test filesystem. Tests can control the contents of the
-// filesystem by providing an appropriate rootFn, which should return a
-// pre-populated root dentry.
-func newTestSystem(t *testing.T, rootFn RootDentryFn) *testutil.System {
-	ctx := contexttest.Context(t)
-	creds := auth.CredentialsFromContext(ctx)
-	v := &vfs.VirtualFilesystem{}
-	if err := v.Init(); err != nil {
-		t.Fatalf("VFS init: %v", err)
-	}
-	v.MustRegisterFilesystemType("testfs", &fsType{rootFn: rootFn}, &vfs.RegisterFilesystemTypeOptions{
-		AllowUserMount: true,
-	})
-	mns, err := v.NewMountNamespace(ctx, creds, "", "testfs", &vfs.GetFilesystemOptions{})
-	if err != nil {
-		t.Fatalf("Failed to create testfs root mount: %v", err)
-	}
-	return testutil.NewSystem(ctx, t, v, mns)
-}
-
-type fsType struct {
-	rootFn RootDentryFn
-}
-
-type filesystem struct {
-	kernfs.Filesystem
-}
-
-type file struct {
-	kernfs.DynamicBytesFile
-	content string
-}
-
-func (fs *filesystem) newFile(creds *auth.Credentials, content string) *kernfs.Dentry {
-	f := &file{}
-	f.content = content
-	f.DynamicBytesFile.Init(creds, fs.NextIno(), f, 0777)
-
-	d := &kernfs.Dentry{}
-	d.Init(f)
-	return d
-}
-
-func (f *file) Generate(ctx context.Context, buf *bytes.Buffer) error {
-	fmt.Fprintf(buf, "%s", f.content)
-	return nil
-}
-
-type attrs struct {
-	kernfs.InodeAttrs
-}
-
-func (*attrs) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
-	return syserror.EPERM
-}
-
-type readonlyDir struct {
-	attrs
-	kernfs.InodeNotSymlink
-	kernfs.InodeNoDynamicLookup
-	kernfs.InodeDirectoryNoNewChildren
-
-	kernfs.OrderedChildren
-	dentry kernfs.Dentry
-}
-
-func (fs *filesystem) newReadonlyDir(creds *auth.Credentials, mode linux.FileMode, contents map[string]*kernfs.Dentry) *kernfs.Dentry {
-	dir := &readonlyDir{}
-	dir.attrs.Init(creds, fs.NextIno(), linux.ModeDirectory|mode)
-	dir.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
-	dir.dentry.Init(dir)
-
-	dir.IncLinks(dir.OrderedChildren.Populate(&dir.dentry, contents))
-
-	return &dir.dentry
-}
-
-func (d *readonlyDir) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
-	if err != nil {
-		return nil, err
-	}
-	return fd.VFSFileDescription(), nil
-}
-
-type dir struct {
-	attrs
-	kernfs.InodeNotSymlink
-	kernfs.InodeNoDynamicLookup
-
-	fs     *filesystem
-	dentry kernfs.Dentry
-	kernfs.OrderedChildren
-}
-
-func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, contents map[string]*kernfs.Dentry) *kernfs.Dentry {
-	dir := &dir{}
-	dir.fs = fs
-	dir.attrs.Init(creds, fs.NextIno(), linux.ModeDirectory|mode)
-	dir.OrderedChildren.Init(kernfs.OrderedChildrenOptions{Writable: true})
-	dir.dentry.Init(dir)
-
-	dir.IncLinks(dir.OrderedChildren.Populate(&dir.dentry, contents))
-
-	return &dir.dentry
-}
-
-func (d *dir) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
-	if err != nil {
-		return nil, err
-	}
-	return fd.VFSFileDescription(), nil
-}
-
-func (d *dir) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error) {
-	creds := auth.CredentialsFromContext(ctx)
-	dir := d.fs.newDir(creds, opts.Mode, nil)
-	dirVFSD := dir.VFSDentry()
-	if err := d.OrderedChildren.Insert(name, dirVFSD); err != nil {
-		dir.DecRef()
-		return nil, err
-	}
-	d.IncLinks(1)
-	return dirVFSD, nil
-}
-
-func (d *dir) NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (*vfs.Dentry, error) {
-	creds := auth.CredentialsFromContext(ctx)
-	f := d.fs.newFile(creds, "")
-	fVFSD := f.VFSDentry()
-	if err := d.OrderedChildren.Insert(name, fVFSD); err != nil {
-		f.DecRef()
-		return nil, err
-	}
-	return fVFSD, nil
-}
-
-func (*dir) NewLink(context.Context, string, kernfs.Inode) (*vfs.Dentry, error) {
-	return nil, syserror.EPERM
-}
-
-func (*dir) NewSymlink(context.Context, string, string) (*vfs.Dentry, error) {
-	return nil, syserror.EPERM
-}
-
-func (*dir) NewNode(context.Context, string, vfs.MknodOptions) (*vfs.Dentry, error) {
-	return nil, syserror.EPERM
-}
-
-func (fsType) Name() string {
-	return "kernfs"
-}
-
-func (fst fsType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opt vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
-	fs := &filesystem{}
-	fs.Init(vfsObj, &fst)
-	root := fst.rootFn(creds, fs)
-	return fs.VFSFilesystem(), root.VFSDentry(), nil
-}
-
-// -------------------- Remainder of the file are test cases --------------------
-
-func TestBasic(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, map[string]*kernfs.Dentry{
-			"file1": fs.newFile(creds, staticFileContent),
-		})
-	})
-	defer sys.Destroy()
-	sys.GetDentryOrDie(sys.PathOpAtRoot("file1")).DecRef()
-}
-
-func TestMkdirGetDentry(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, map[string]*kernfs.Dentry{
-			"dir1": fs.newDir(creds, 0755, nil),
-		})
-	})
-	defer sys.Destroy()
-
-	pop := sys.PathOpAtRoot("dir1/a new directory")
-	if err := sys.VFS.MkdirAt(sys.Ctx, sys.Creds, pop, &vfs.MkdirOptions{Mode: 0755}); err != nil {
-		t.Fatalf("MkdirAt for PathOperation %+v failed: %v", pop, err)
-	}
-	sys.GetDentryOrDie(pop).DecRef()
-}
-
-func TestReadStaticFile(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, map[string]*kernfs.Dentry{
-			"file1": fs.newFile(creds, staticFileContent),
-		})
-	})
-	defer sys.Destroy()
-
-	pop := sys.PathOpAtRoot("file1")
-	fd, err := sys.VFS.OpenAt(sys.Ctx, sys.Creds, pop, &vfs.OpenOptions{
-		Flags: linux.O_RDONLY,
-	})
-	if err != nil {
-		t.Fatalf("OpenAt for PathOperation %+v failed: %v", pop, err)
-	}
-	defer fd.DecRef()
-
-	content, err := sys.ReadToEnd(fd)
-	if err != nil {
-		t.Fatalf("Read failed: %v", err)
-	}
-	if diff := cmp.Diff(staticFileContent, content); diff != "" {
-		t.Fatalf("Read returned unexpected data:\n--- want\n+++ got\n%v", diff)
-	}
-}
-
-func TestCreateNewFileInStaticDir(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, map[string]*kernfs.Dentry{
-			"dir1": fs.newDir(creds, 0755, nil),
-		})
-	})
-	defer sys.Destroy()
-
-	pop := sys.PathOpAtRoot("dir1/newfile")
-	opts := &vfs.OpenOptions{Flags: linux.O_CREAT | linux.O_EXCL, Mode: defaultMode}
-	fd, err := sys.VFS.OpenAt(sys.Ctx, sys.Creds, pop, opts)
-	if err != nil {
-		t.Fatalf("OpenAt(pop:%+v, opts:%+v) failed: %v", pop, opts, err)
-	}
-
-	// Close the file. The file should persist.
-	fd.DecRef()
-
-	fd, err = sys.VFS.OpenAt(sys.Ctx, sys.Creds, pop, &vfs.OpenOptions{
-		Flags: linux.O_RDONLY,
-	})
-	if err != nil {
-		t.Fatalf("OpenAt(pop:%+v) = %+v failed: %v", pop, fd, err)
-	}
-	fd.DecRef()
-}
-
-func TestDirFDReadWrite(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, nil)
-	})
-	defer sys.Destroy()
-
-	pop := sys.PathOpAtRoot("/")
-	fd, err := sys.VFS.OpenAt(sys.Ctx, sys.Creds, pop, &vfs.OpenOptions{
-		Flags: linux.O_RDONLY,
-	})
-	if err != nil {
-		t.Fatalf("OpenAt for PathOperation %+v failed: %v", pop, err)
-	}
-	defer fd.DecRef()
-
-	// Read/Write should fail for directory FDs.
-	if _, err := fd.Read(sys.Ctx, usermem.BytesIOSequence([]byte{}), vfs.ReadOptions{}); err != syserror.EISDIR {
-		t.Fatalf("Read for directory FD failed with unexpected error: %v", err)
-	}
-	if _, err := fd.Write(sys.Ctx, usermem.BytesIOSequence([]byte{}), vfs.WriteOptions{}); err != syserror.EBADF {
-		t.Fatalf("Write for directory FD failed with unexpected error: %v", err)
-	}
-}
-
-func TestDirFDIterDirents(t *testing.T) {
-	sys := newTestSystem(t, func(creds *auth.Credentials, fs *filesystem) *kernfs.Dentry {
-		return fs.newReadonlyDir(creds, 0755, map[string]*kernfs.Dentry{
-			// Fill root with nodes backed by various inode implementations.
-			"dir1": fs.newReadonlyDir(creds, 0755, nil),
-			"dir2": fs.newDir(creds, 0755, map[string]*kernfs.Dentry{
-				"dir3": fs.newDir(creds, 0755, nil),
-			}),
-			"file1": fs.newFile(creds, staticFileContent),
-		})
-	})
-	defer sys.Destroy()
-
-	pop := sys.PathOpAtRoot("/")
-	sys.AssertAllDirentTypes(sys.ListDirents(pop), map[string]testutil.DirentType{
-		"dir1":  linux.DT_DIR,
-		"dir2":  linux.DT_DIR,
-		"file1": linux.DT_REG,
-	})
-}
diff --git a/pkg/sentry/fsimpl/kernfs/slot_list.go b/pkg/sentry/fsimpl/kernfs/slot_list.go
new file mode 100755
index 000000000..09c30bca7
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/slot_list.go
@@ -0,0 +1,193 @@
+package kernfs
+
+// ElementMapper provides an identity mapping by default.
+//
+// This can be replaced to provide a struct that maps elements to linker
+// objects, if they are not the same. An ElementMapper is not typically
+// required if: Linker is left as is, Element is left as is, or Linker and
+// Element are the same type.
+type slotElementMapper struct{}
+
+// linkerFor maps an Element to a Linker.
+//
+// This default implementation should be inlined.
+//
+//go:nosplit
+func (slotElementMapper) linkerFor(elem *slot) *slot { return elem }
+
+// List is an intrusive list. Entries can be added to or removed from the list
+// in O(1) time and with no additional memory allocations.
+//
+// The zero value for List is an empty list ready to use.
+//
+// To iterate over a list (where l is a List):
+//      for e := l.Front(); e != nil; e = e.Next() {
+// 		// do something with e.
+//      }
+//
+// +stateify savable
+type slotList struct {
+	head *slot
+	tail *slot
+}
+
+// Reset resets list l to the empty state.
+func (l *slotList) Reset() {
+	l.head = nil
+	l.tail = nil
+}
+
+// Empty returns true iff the list is empty.
+func (l *slotList) Empty() bool {
+	return l.head == nil
+}
+
+// Front returns the first element of list l or nil.
+func (l *slotList) Front() *slot {
+	return l.head
+}
+
+// Back returns the last element of list l or nil.
+func (l *slotList) Back() *slot {
+	return l.tail
+}
+
+// Len returns the number of elements in the list.
+//
+// NOTE: This is an O(n) operation.
+func (l *slotList) Len() (count int) {
+	for e := l.Front(); e != nil; e = e.Next() {
+		count++
+	}
+	return count
+}
+
+// PushFront inserts the element e at the front of list l.
+func (l *slotList) PushFront(e *slot) {
+	linker := slotElementMapper{}.linkerFor(e)
+	linker.SetNext(l.head)
+	linker.SetPrev(nil)
+	if l.head != nil {
+		slotElementMapper{}.linkerFor(l.head).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+
+	l.head = e
+}
+
+// PushBack inserts the element e at the back of list l.
+func (l *slotList) PushBack(e *slot) {
+	linker := slotElementMapper{}.linkerFor(e)
+	linker.SetNext(nil)
+	linker.SetPrev(l.tail)
+	if l.tail != nil {
+		slotElementMapper{}.linkerFor(l.tail).SetNext(e)
+	} else {
+		l.head = e
+	}
+
+	l.tail = e
+}
+
+// PushBackList inserts list m at the end of list l, emptying m.
+func (l *slotList) PushBackList(m *slotList) {
+	if l.head == nil {
+		l.head = m.head
+		l.tail = m.tail
+	} else if m.head != nil {
+		slotElementMapper{}.linkerFor(l.tail).SetNext(m.head)
+		slotElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
+
+		l.tail = m.tail
+	}
+	m.head = nil
+	m.tail = nil
+}
+
+// InsertAfter inserts e after b.
+func (l *slotList) InsertAfter(b, e *slot) {
+	bLinker := slotElementMapper{}.linkerFor(b)
+	eLinker := slotElementMapper{}.linkerFor(e)
+
+	a := bLinker.Next()
+
+	eLinker.SetNext(a)
+	eLinker.SetPrev(b)
+	bLinker.SetNext(e)
+
+	if a != nil {
+		slotElementMapper{}.linkerFor(a).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+}
+
+// InsertBefore inserts e before a.
+func (l *slotList) InsertBefore(a, e *slot) {
+	aLinker := slotElementMapper{}.linkerFor(a)
+	eLinker := slotElementMapper{}.linkerFor(e)
+
+	b := aLinker.Prev()
+	eLinker.SetNext(a)
+	eLinker.SetPrev(b)
+	aLinker.SetPrev(e)
+
+	if b != nil {
+		slotElementMapper{}.linkerFor(b).SetNext(e)
+	} else {
+		l.head = e
+	}
+}
+
+// Remove removes e from l.
+func (l *slotList) Remove(e *slot) {
+	linker := slotElementMapper{}.linkerFor(e)
+	prev := linker.Prev()
+	next := linker.Next()
+
+	if prev != nil {
+		slotElementMapper{}.linkerFor(prev).SetNext(next)
+	} else {
+		l.head = next
+	}
+
+	if next != nil {
+		slotElementMapper{}.linkerFor(next).SetPrev(prev)
+	} else {
+		l.tail = prev
+	}
+
+	linker.SetNext(nil)
+	linker.SetPrev(nil)
+}
+
+// Entry is a default implementation of Linker. Users can add anonymous fields
+// of this type to their structs to make them automatically implement the
+// methods needed by List.
+//
+// +stateify savable
+type slotEntry struct {
+	next *slot
+	prev *slot
+}
+
+// Next returns the entry that follows e in the list.
+func (e *slotEntry) Next() *slot {
+	return e.next
+}
+
+// Prev returns the entry that precedes e in the list.
+func (e *slotEntry) Prev() *slot {
+	return e.prev
+}
+
+// SetNext assigns 'entry' as the entry that follows e in the list.
+func (e *slotEntry) SetNext(elem *slot) {
+	e.next = elem
+}
+
+// SetPrev assigns 'entry' as the entry that precedes e in the list.
+func (e *slotEntry) SetPrev(elem *slot) {
+	e.prev = elem
+}
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index 0aa6dc979..0aa6dc979 100644..100755
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go