12 files changed, 2588 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
new file mode 100755
index 000000000..d8bddbafa
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
@@ -0,0 +1,133 @@
+// 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
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// DynamicBytesFile implements kernfs.Inode and represents a read-only
+// file whose contents are backed by a vfs.DynamicBytesSource.
+//
+// Must be instantiated with NewDynamicBytesFile or initialized with Init
+// before first use.
+//
+// +stateify savable
+type DynamicBytesFile struct {
+	InodeAttrs
+	InodeNoopRefCount
+	InodeNotDirectory
+	InodeNotSymlink
+
+	data vfs.DynamicBytesSource
+}
+
+var _ Inode = (*DynamicBytesFile)(nil)
+
+// Init initializes a dynamic bytes file.
+func (f *DynamicBytesFile) Init(creds *auth.Credentials, ino uint64, data vfs.DynamicBytesSource, perm linux.FileMode) {
+	if perm&^linux.PermissionsMask != 0 {
+		panic(fmt.Sprintf("Only permission mask must be set: %x", perm&linux.PermissionsMask))
+	}
+	f.InodeAttrs.Init(creds, ino, linux.ModeRegular|perm)
+	f.data = data
+}
+
+// Open implements Inode.Open.
+func (f *DynamicBytesFile) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &DynamicBytesFD{}
+	if err := fd.Init(rp.Mount(), vfsd, f.data, opts.Flags); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+// SetStat implements Inode.SetStat. By default DynamicBytesFile doesn't allow
+// inode attributes to be changed. Override SetStat() making it call
+// f.InodeAttrs to allow it.
+func (*DynamicBytesFile) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
+
+// DynamicBytesFD implements vfs.FileDescriptionImpl for an FD backed by a
+// DynamicBytesFile.
+//
+// Must be initialized with Init before first use.
+//
+// +stateify savable
+type DynamicBytesFD struct {
+	vfs.FileDescriptionDefaultImpl
+	vfs.DynamicBytesFileDescriptionImpl
+
+	vfsfd vfs.FileDescription
+	inode Inode
+}
+
+// Init initializes a DynamicBytesFD.
+func (fd *DynamicBytesFD) Init(m *vfs.Mount, d *vfs.Dentry, data vfs.DynamicBytesSource, flags uint32) error {
+	if err := fd.vfsfd.Init(fd, flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
+		return err
+	}
+	fd.inode = d.Impl().(*Dentry).inode
+	fd.SetDataSource(data)
+	return nil
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *DynamicBytesFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	return fd.DynamicBytesFileDescriptionImpl.Seek(ctx, offset, whence)
+}
+
+// Read implmenets vfs.FileDescriptionImpl.Read.
+func (fd *DynamicBytesFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	return fd.DynamicBytesFileDescriptionImpl.Read(ctx, dst, opts)
+}
+
+// PRead implmenets vfs.FileDescriptionImpl.PRead.
+func (fd *DynamicBytesFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return fd.DynamicBytesFileDescriptionImpl.PRead(ctx, dst, offset, opts)
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *DynamicBytesFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	return fd.DynamicBytesFileDescriptionImpl.Write(ctx, src, opts)
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *DynamicBytesFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return fd.DynamicBytesFileDescriptionImpl.PWrite(ctx, src, offset, opts)
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *DynamicBytesFD) Release() {}
+
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *DynamicBytesFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	fs := fd.vfsfd.VirtualDentry().Mount().Filesystem()
+	return fd.inode.Stat(fs, opts)
+}
+
+// SetStat implements vfs.FileDescriptionImpl.SetStat.
+func (fd *DynamicBytesFD) SetStat(context.Context, vfs.SetStatOptions) error {
+	// DynamicBytesFiles are immutable.
+	return syserror.EPERM
+}
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
new file mode 100755
index 000000000..bfa786c88
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
@@ -0,0 +1,212 @@
+// 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
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// GenericDirectoryFD implements vfs.FileDescriptionImpl for a generic directory
+// inode that uses OrderChildren to track child nodes. GenericDirectoryFD is not
+// compatible with dynamic directories.
+//
+// Note that GenericDirectoryFD holds a lock over OrderedChildren while calling
+// IterDirents callback. The IterDirents callback therefore cannot hash or
+// unhash children, or recursively call IterDirents on the same underlying
+// inode.
+//
+// Must be initialize with Init before first use.
+type GenericDirectoryFD struct {
+	vfs.FileDescriptionDefaultImpl
+	vfs.DirectoryFileDescriptionDefaultImpl
+
+	vfsfd    vfs.FileDescription
+	children *OrderedChildren
+	off      int64
+}
+
+// Init initializes a GenericDirectoryFD.
+func (fd *GenericDirectoryFD) Init(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, opts *vfs.OpenOptions) error {
+	if vfs.AccessTypesForOpenFlags(opts)&vfs.MayWrite != 0 {
+		// Can't open directories for writing.
+		return syserror.EISDIR
+	}
+	if err := fd.vfsfd.Init(fd, opts.Flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
+		return err
+	}
+	fd.children = children
+	return nil
+}
+
+// VFSFileDescription returns a pointer to the vfs.FileDescription representing
+// this object.
+func (fd *GenericDirectoryFD) VFSFileDescription() *vfs.FileDescription {
+	return &fd.vfsfd
+}
+
+// ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
+func (fd *GenericDirectoryFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	return fd.FileDescriptionDefaultImpl.ConfigureMMap(ctx, opts)
+}
+
+// Read implmenets vfs.FileDescriptionImpl.Read.
+func (fd *GenericDirectoryFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	return fd.DirectoryFileDescriptionDefaultImpl.Read(ctx, dst, opts)
+}
+
+// PRead implmenets vfs.FileDescriptionImpl.PRead.
+func (fd *GenericDirectoryFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return fd.DirectoryFileDescriptionDefaultImpl.PRead(ctx, dst, offset, opts)
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *GenericDirectoryFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	return fd.DirectoryFileDescriptionDefaultImpl.Write(ctx, src, opts)
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *GenericDirectoryFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return fd.DirectoryFileDescriptionDefaultImpl.PWrite(ctx, src, offset, opts)
+}
+
+// Release implements vfs.FileDecriptionImpl.Release.
+func (fd *GenericDirectoryFD) Release() {}
+
+func (fd *GenericDirectoryFD) filesystem() *vfs.Filesystem {
+	return fd.vfsfd.VirtualDentry().Mount().Filesystem()
+}
+
+func (fd *GenericDirectoryFD) inode() Inode {
+	return fd.vfsfd.VirtualDentry().Dentry().Impl().(*Dentry).inode
+}
+
+// IterDirents implements vfs.FileDecriptionImpl.IterDirents. IterDirents holds
+// o.mu when calling cb.
+func (fd *GenericDirectoryFD) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback) error {
+	vfsFS := fd.filesystem()
+	fs := vfsFS.Impl().(*Filesystem)
+	vfsd := fd.vfsfd.VirtualDentry().Dentry()
+
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+
+	opts := vfs.StatOptions{Mask: linux.STATX_INO}
+	// Handle ".".
+	if fd.off == 0 {
+		stat, err := fd.inode().Stat(vfsFS, opts)
+		if err != nil {
+			return err
+		}
+		dirent := vfs.Dirent{
+			Name:    ".",
+			Type:    linux.DT_DIR,
+			Ino:     stat.Ino,
+			NextOff: 1,
+		}
+		if err := cb.Handle(dirent); err != nil {
+			return err
+		}
+		fd.off++
+	}
+
+	// Handle "..".
+	if fd.off == 1 {
+		parentInode := vfsd.ParentOrSelf().Impl().(*Dentry).inode
+		stat, err := parentInode.Stat(vfsFS, opts)
+		if err != nil {
+			return err
+		}
+		dirent := vfs.Dirent{
+			Name:    "..",
+			Type:    linux.FileMode(stat.Mode).DirentType(),
+			Ino:     stat.Ino,
+			NextOff: 2,
+		}
+		if err := cb.Handle(dirent); err != nil {
+			return err
+		}
+		fd.off++
+	}
+
+	// Handle static children.
+	fd.children.mu.RLock()
+	defer fd.children.mu.RUnlock()
+	// fd.off accounts for "." and "..", but fd.children do not track
+	// these.
+	childIdx := fd.off - 2
+	for it := fd.children.nthLocked(childIdx); it != nil; it = it.Next() {
+		inode := it.Dentry.Impl().(*Dentry).inode
+		stat, err := inode.Stat(vfsFS, opts)
+		if err != nil {
+			return err
+		}
+		dirent := vfs.Dirent{
+			Name:    it.Name,
+			Type:    linux.FileMode(stat.Mode).DirentType(),
+			Ino:     stat.Ino,
+			NextOff: fd.off + 1,
+		}
+		if err := cb.Handle(dirent); err != nil {
+			return err
+		}
+		fd.off++
+	}
+
+	var err error
+	relOffset := fd.off - int64(len(fd.children.set)) - 2
+	fd.off, err = fd.inode().IterDirents(ctx, cb, fd.off, relOffset)
+	return err
+}
+
+// Seek implements vfs.FileDecriptionImpl.Seek.
+func (fd *GenericDirectoryFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	fs := fd.filesystem().Impl().(*Filesystem)
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+
+	switch whence {
+	case linux.SEEK_SET:
+		// Use offset as given.
+	case linux.SEEK_CUR:
+		offset += fd.off
+	default:
+		return 0, syserror.EINVAL
+	}
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+	fd.off = offset
+	return offset, nil
+}
+
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *GenericDirectoryFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	fs := fd.filesystem()
+	inode := fd.inode()
+	return inode.Stat(fs, opts)
+}
+
+// SetStat implements vfs.FileDescriptionImpl.SetStat.
+func (fd *GenericDirectoryFD) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
+	creds := auth.CredentialsFromContext(ctx)
+	inode := fd.vfsfd.VirtualDentry().Dentry().Impl().(*Dentry).inode
+	return inode.SetStat(ctx, fd.filesystem(), creds, opts)
+}
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
new file mode 100755
index 000000000..a429fa23d
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -0,0 +1,801 @@
+// 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
+
+// This file implements vfs.FilesystemImpl for kernfs.
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// stepExistingLocked resolves rp.Component() in parent directory vfsd.
+//
+// stepExistingLocked is loosely analogous to fs/namei.c:walk_component().
+//
+// Preconditions: Filesystem.mu must be locked for at least reading. !rp.Done().
+//
+// Postcondition: Caller must call fs.processDeferredDecRefs*.
+func (fs *Filesystem) stepExistingLocked(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry) (*vfs.Dentry, error) {
+	d := vfsd.Impl().(*Dentry)
+	if !d.isDir() {
+		return nil, syserror.ENOTDIR
+	}
+	// Directory searchable?
+	if err := d.inode.CheckPermissions(ctx, rp.Credentials(), vfs.MayExec); err != nil {
+		return nil, err
+	}
+afterSymlink:
+	name := rp.Component()
+	// Revalidation must be skipped if name is "." or ".."; d or its parent
+	// respectively can't be expected to transition from invalidated back to
+	// valid, so detecting invalidation and retrying would loop forever. This
+	// is consistent with Linux: fs/namei.c:walk_component() => lookup_fast()
+	// calls d_revalidate(), but walk_component() => handle_dots() does not.
+	if name == "." {
+		rp.Advance()
+		return vfsd, nil
+	}
+	if name == ".." {
+		nextVFSD, err := rp.ResolveParent(vfsd)
+		if err != nil {
+			return nil, err
+		}
+		rp.Advance()
+		return nextVFSD, nil
+	}
+	d.dirMu.Lock()
+	nextVFSD, err := rp.ResolveChild(vfsd, name)
+	if err != nil {
+		d.dirMu.Unlock()
+		return nil, err
+	}
+	next, err := fs.revalidateChildLocked(ctx, rp.VirtualFilesystem(), d, name, nextVFSD)
+	d.dirMu.Unlock()
+	if err != nil {
+		return nil, err
+	}
+	// Resolve any symlink at current path component.
+	if rp.ShouldFollowSymlink() && next.isSymlink() {
+		// TODO: VFS2 needs something extra for /proc/[pid]/fd/ "magic symlinks".
+		target, err := next.inode.Readlink(ctx)
+		if err != nil {
+			return nil, err
+		}
+		if err := rp.HandleSymlink(target); err != nil {
+			return nil, err
+		}
+		goto afterSymlink
+
+	}
+	rp.Advance()
+	return &next.vfsd, nil
+}
+
+// revalidateChildLocked must be called after a call to parent.vfsd.Child(name)
+// or vfs.ResolvingPath.ResolveChild(name) returns childVFSD (which may be
+// nil) to verify that the returned child (or lack thereof) is correct.
+//
+// Preconditions: Filesystem.mu must be locked for at least reading.
+// parent.dirMu must be locked. parent.isDir(). name is not "." or "..".
+//
+// Postconditions: Caller must call fs.processDeferredDecRefs*.
+func (fs *Filesystem) revalidateChildLocked(ctx context.Context, vfsObj *vfs.VirtualFilesystem, parent *Dentry, name string, childVFSD *vfs.Dentry) (*Dentry, error) {
+	if childVFSD != nil {
+		// Cached dentry exists, revalidate.
+		child := childVFSD.Impl().(*Dentry)
+		if !child.inode.Valid(ctx) {
+			vfsObj.ForceDeleteDentry(childVFSD)
+			fs.deferDecRef(childVFSD) // Reference from Lookup.
+			childVFSD = nil
+		}
+	}
+	if childVFSD == nil {
+		// Dentry isn't cached; it either doesn't exist or failed
+		// revalidation. Attempt to resolve it via Lookup.
+		//
+		// FIXME(gvisor.dev/issue/1193): Inode.Lookup() should return
+		// *(kernfs.)Dentry, not *vfs.Dentry, since (kernfs.)Filesystem assumes
+		// that all dentries in the filesystem are (kernfs.)Dentry and performs
+		// vfs.DentryImpl casts accordingly.
+		var err error
+		childVFSD, err = parent.inode.Lookup(ctx, name)
+		if err != nil {
+			return nil, err
+		}
+		// Reference on childVFSD dropped by a corresponding Valid.
+		parent.insertChildLocked(name, childVFSD)
+	}
+	return childVFSD.Impl().(*Dentry), nil
+}
+
+// walkExistingLocked resolves rp to an existing file.
+//
+// walkExistingLocked is loosely analogous to Linux's
+// fs/namei.c:path_lookupat().
+//
+// Preconditions: Filesystem.mu must be locked for at least reading.
+//
+// Postconditions: Caller must call fs.processDeferredDecRefs*.
+func (fs *Filesystem) walkExistingLocked(ctx context.Context, rp *vfs.ResolvingPath) (*vfs.Dentry, Inode, error) {
+	vfsd := rp.Start()
+	for !rp.Done() {
+		var err error
+		vfsd, err = fs.stepExistingLocked(ctx, rp, vfsd)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	d := vfsd.Impl().(*Dentry)
+	if rp.MustBeDir() && !d.isDir() {
+		return nil, nil, syserror.ENOTDIR
+	}
+	return vfsd, d.inode, nil
+}
+
+// walkParentDirLocked resolves all but the last path component of rp to an
+// existing directory. It does not check that the returned directory is
+// searchable by the provider of rp.
+//
+// walkParentDirLocked is loosely analogous to Linux's
+// fs/namei.c:path_parentat().
+//
+// Preconditions: Filesystem.mu must be locked for at least reading. !rp.Done().
+//
+// Postconditions: Caller must call fs.processDeferredDecRefs*.
+func (fs *Filesystem) walkParentDirLocked(ctx context.Context, rp *vfs.ResolvingPath) (*vfs.Dentry, Inode, error) {
+	vfsd := rp.Start()
+	for !rp.Final() {
+		var err error
+		vfsd, err = fs.stepExistingLocked(ctx, rp, vfsd)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	d := vfsd.Impl().(*Dentry)
+	if !d.isDir() {
+		return nil, nil, syserror.ENOTDIR
+	}
+	return vfsd, d.inode, nil
+}
+
+// checkCreateLocked checks that a file named rp.Component() may be created in
+// directory parentVFSD, then returns rp.Component().
+//
+// Preconditions: Filesystem.mu must be locked for at least reading. parentInode
+// == parentVFSD.Impl().(*Dentry).Inode. isDir(parentInode) == true.
+func checkCreateLocked(ctx context.Context, rp *vfs.ResolvingPath, parentVFSD *vfs.Dentry, parentInode Inode) (string, error) {
+	if err := parentInode.CheckPermissions(ctx, rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
+		return "", err
+	}
+	pc := rp.Component()
+	if pc == "." || pc == ".." {
+		return "", syserror.EEXIST
+	}
+	childVFSD, err := rp.ResolveChild(parentVFSD, pc)
+	if err != nil {
+		return "", err
+	}
+	if childVFSD != nil {
+		return "", syserror.EEXIST
+	}
+	if parentVFSD.IsDisowned() {
+		return "", syserror.ENOENT
+	}
+	return pc, nil
+}
+
+// checkDeleteLocked checks that the file represented by vfsd may be deleted.
+//
+// Preconditions: Filesystem.mu must be locked for at least reading.
+func checkDeleteLocked(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry) error {
+	parentVFSD := vfsd.Parent()
+	if parentVFSD == nil {
+		return syserror.EBUSY
+	}
+	if parentVFSD.IsDisowned() {
+		return syserror.ENOENT
+	}
+	if err := parentVFSD.Impl().(*Dentry).inode.CheckPermissions(ctx, rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Release implements vfs.FilesystemImpl.Release.
+func (fs *Filesystem) Release() {
+}
+
+// Sync implements vfs.FilesystemImpl.Sync.
+func (fs *Filesystem) Sync(ctx context.Context) error {
+	// All filesystem state is in-memory.
+	return nil
+}
+
+// AccessAt implements vfs.Filesystem.Impl.AccessAt.
+func (fs *Filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+	defer fs.processDeferredDecRefs()
+
+	_, inode, err := fs.walkExistingLocked(ctx, rp)
+	if err != nil {
+		return err
+	}
+	return inode.CheckPermissions(ctx, creds, ats)
+}
+
+// GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
+func (fs *Filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
+	fs.mu.RLock()
+	defer fs.processDeferredDecRefs()
+	defer fs.mu.RUnlock()
+	vfsd, inode, err := fs.walkExistingLocked(ctx, rp)
+	if err != nil {
+		return nil, err
+	}
+
+	if opts.CheckSearchable {
+		d := vfsd.Impl().(*Dentry)
+		if !d.isDir() {
+			return nil, syserror.ENOTDIR
+		}
+		if err := inode.CheckPermissions(ctx, rp.Credentials(), vfs.MayExec); err != nil {
+			return nil, err
+		}
+	}
+	vfsd.IncRef() // Ownership transferred to caller.
+	return vfsd, nil
+}
+
+// GetParentDentryAt implements vfs.FilesystemImpl.GetParentDentryAt.
+func (fs *Filesystem) GetParentDentryAt(ctx context.Context, rp *vfs.ResolvingPath) (*vfs.Dentry, error) {
+	fs.mu.RLock()
+	defer fs.processDeferredDecRefs()
+	defer fs.mu.RUnlock()
+	vfsd, _, err := fs.walkParentDirLocked(ctx, rp)
+	if err != nil {
+		return nil, err
+	}
+	vfsd.IncRef() // Ownership transferred to caller.
+	return vfsd, nil
+}
+
+// LinkAt implements vfs.FilesystemImpl.LinkAt.
+func (fs *Filesystem) LinkAt(ctx context.Context, rp *vfs.ResolvingPath, vd vfs.VirtualDentry) error {
+	if rp.Done() {
+		return syserror.EEXIST
+	}
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	pc, err := checkCreateLocked(ctx, rp, parentVFSD, parentInode)
+	if err != nil {
+		return err
+	}
+	if rp.Mount() != vd.Mount() {
+		return syserror.EXDEV
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+
+	d := vd.Dentry().Impl().(*Dentry)
+	if d.isDir() {
+		return syserror.EPERM
+	}
+
+	child, err := parentInode.NewLink(ctx, pc, d.inode)
+	if err != nil {
+		return err
+	}
+	parentVFSD.Impl().(*Dentry).InsertChild(pc, child)
+	return nil
+}
+
+// MkdirAt implements vfs.FilesystemImpl.MkdirAt.
+func (fs *Filesystem) MkdirAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.MkdirOptions) error {
+	if rp.Done() {
+		return syserror.EEXIST
+	}
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	pc, err := checkCreateLocked(ctx, rp, parentVFSD, parentInode)
+	if err != nil {
+		return err
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	child, err := parentInode.NewDir(ctx, pc, opts)
+	if err != nil {
+		return err
+	}
+	parentVFSD.Impl().(*Dentry).InsertChild(pc, child)
+	return nil
+}
+
+// MknodAt implements vfs.FilesystemImpl.MknodAt.
+func (fs *Filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.MknodOptions) error {
+	if rp.Done() {
+		return syserror.EEXIST
+	}
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	pc, err := checkCreateLocked(ctx, rp, parentVFSD, parentInode)
+	if err != nil {
+		return err
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	new, err := parentInode.NewNode(ctx, pc, opts)
+	if err != nil {
+		return err
+	}
+	parentVFSD.Impl().(*Dentry).InsertChild(pc, new)
+	return nil
+}
+
+// OpenAt implements vfs.FilesystemImpl.OpenAt.
+func (fs *Filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	// Filter out flags that are not supported by kernfs. O_DIRECTORY and
+	// O_NOFOLLOW have no effect here (they're handled by VFS by setting
+	// appropriate bits in rp), but are returned by
+	// FileDescriptionImpl.StatusFlags().
+	opts.Flags &= linux.O_ACCMODE | linux.O_CREAT | linux.O_EXCL | linux.O_TRUNC | linux.O_DIRECTORY | linux.O_NOFOLLOW
+	ats := vfs.AccessTypesForOpenFlags(&opts)
+
+	// Do not create new file.
+	if opts.Flags&linux.O_CREAT == 0 {
+		fs.mu.RLock()
+		defer fs.processDeferredDecRefs()
+		defer fs.mu.RUnlock()
+		vfsd, inode, err := fs.walkExistingLocked(ctx, rp)
+		if err != nil {
+			return nil, err
+		}
+		if err := inode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
+			return nil, err
+		}
+		return inode.Open(rp, vfsd, opts)
+	}
+
+	// May create new file.
+	mustCreate := opts.Flags&linux.O_EXCL != 0
+	vfsd := rp.Start()
+	inode := vfsd.Impl().(*Dentry).inode
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	if rp.Done() {
+		if rp.MustBeDir() {
+			return nil, syserror.EISDIR
+		}
+		if mustCreate {
+			return nil, syserror.EEXIST
+		}
+		if err := inode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
+			return nil, err
+		}
+		return inode.Open(rp, vfsd, opts)
+	}
+afterTrailingSymlink:
+	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return nil, err
+	}
+	// Check for search permission in the parent directory.
+	if err := parentInode.CheckPermissions(ctx, rp.Credentials(), vfs.MayExec); err != nil {
+		return nil, err
+	}
+	// Reject attempts to open directories with O_CREAT.
+	if rp.MustBeDir() {
+		return nil, syserror.EISDIR
+	}
+	pc := rp.Component()
+	if pc == "." || pc == ".." {
+		return nil, syserror.EISDIR
+	}
+	// Determine whether or not we need to create a file.
+	childVFSD, err := rp.ResolveChild(parentVFSD, pc)
+	if err != nil {
+		return nil, err
+	}
+	if childVFSD == nil {
+		// Already checked for searchability above; now check for writability.
+		if err := parentInode.CheckPermissions(ctx, rp.Credentials(), vfs.MayWrite); err != nil {
+			return nil, err
+		}
+		if err := rp.Mount().CheckBeginWrite(); err != nil {
+			return nil, err
+		}
+		defer rp.Mount().EndWrite()
+		// Create and open the child.
+		child, err := parentInode.NewFile(ctx, pc, opts)
+		if err != nil {
+			return nil, err
+		}
+		parentVFSD.Impl().(*Dentry).InsertChild(pc, child)
+		return child.Impl().(*Dentry).inode.Open(rp, child, opts)
+	}
+	// Open existing file or follow symlink.
+	if mustCreate {
+		return nil, syserror.EEXIST
+	}
+	childDentry := childVFSD.Impl().(*Dentry)
+	childInode := childDentry.inode
+	if rp.ShouldFollowSymlink() {
+		if childDentry.isSymlink() {
+			target, err := childInode.Readlink(ctx)
+			if err != nil {
+				return nil, err
+			}
+			if err := rp.HandleSymlink(target); err != nil {
+				return nil, err
+			}
+			// rp.Final() may no longer be true since we now need to resolve the
+			// symlink target.
+			goto afterTrailingSymlink
+		}
+	}
+	if err := childInode.CheckPermissions(ctx, rp.Credentials(), ats); err != nil {
+		return nil, err
+	}
+	return childInode.Open(rp, childVFSD, opts)
+}
+
+// ReadlinkAt implements vfs.FilesystemImpl.ReadlinkAt.
+func (fs *Filesystem) ReadlinkAt(ctx context.Context, rp *vfs.ResolvingPath) (string, error) {
+	fs.mu.RLock()
+	d, inode, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return "", err
+	}
+	if !d.Impl().(*Dentry).isSymlink() {
+		return "", syserror.EINVAL
+	}
+	return inode.Readlink(ctx)
+}
+
+// RenameAt implements vfs.FilesystemImpl.RenameAt.
+func (fs *Filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldParentVD vfs.VirtualDentry, oldName string, opts vfs.RenameOptions) error {
+	// Only RENAME_NOREPLACE is supported.
+	if opts.Flags&^linux.RENAME_NOREPLACE != 0 {
+		return syserror.EINVAL
+	}
+	noReplace := opts.Flags&linux.RENAME_NOREPLACE != 0
+
+	fs.mu.Lock()
+	defer fs.mu.Lock()
+
+	// Resolve the destination directory first to verify that it's on this
+	// Mount.
+	dstDirVFSD, dstDirInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	mnt := rp.Mount()
+	if mnt != oldParentVD.Mount() {
+		return syserror.EXDEV
+	}
+	if err := mnt.CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer mnt.EndWrite()
+
+	srcDirVFSD := oldParentVD.Dentry()
+	srcDir := srcDirVFSD.Impl().(*Dentry)
+	srcDir.dirMu.Lock()
+	src, err := fs.revalidateChildLocked(ctx, rp.VirtualFilesystem(), srcDir, oldName, srcDirVFSD.Child(oldName))
+	srcDir.dirMu.Unlock()
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	srcVFSD := &src.vfsd
+
+	// Can we remove the src dentry?
+	if err := checkDeleteLocked(ctx, rp, srcVFSD); err != nil {
+		return err
+	}
+
+	// Can we create the dst dentry?
+	var dstVFSD *vfs.Dentry
+	pc, err := checkCreateLocked(ctx, rp, dstDirVFSD, dstDirInode)
+	switch err {
+	case nil:
+		// Ok, continue with rename as replacement.
+	case syserror.EEXIST:
+		if noReplace {
+			// Won't overwrite existing node since RENAME_NOREPLACE was requested.
+			return syserror.EEXIST
+		}
+		dstVFSD, err = rp.ResolveChild(dstDirVFSD, pc)
+		if err != nil {
+			panic(fmt.Sprintf("Child %q for parent Dentry %+v disappeared inside atomic section?", pc, dstDirVFSD))
+		}
+	default:
+		return err
+	}
+
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	virtfs := rp.VirtualFilesystem()
+
+	srcDirDentry := srcDirVFSD.Impl().(*Dentry)
+	dstDirDentry := dstDirVFSD.Impl().(*Dentry)
+
+	// We can't deadlock here due to lock ordering because we're protected from
+	// concurrent renames by fs.mu held for writing.
+	srcDirDentry.dirMu.Lock()
+	defer srcDirDentry.dirMu.Unlock()
+	dstDirDentry.dirMu.Lock()
+	defer dstDirDentry.dirMu.Unlock()
+
+	if err := virtfs.PrepareRenameDentry(mntns, srcVFSD, dstVFSD); err != nil {
+		return err
+	}
+	srcDirInode := srcDirDentry.inode
+	replaced, err := srcDirInode.Rename(ctx, srcVFSD.Name(), pc, srcVFSD, dstDirVFSD)
+	if err != nil {
+		virtfs.AbortRenameDentry(srcVFSD, dstVFSD)
+		return err
+	}
+	virtfs.CommitRenameReplaceDentry(srcVFSD, dstDirVFSD, pc, replaced)
+	return nil
+}
+
+// RmdirAt implements vfs.FilesystemImpl.RmdirAt.
+func (fs *Filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error {
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	vfsd, inode, err := fs.walkExistingLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	if err := checkDeleteLocked(ctx, rp, vfsd); err != nil {
+		return err
+	}
+	if !vfsd.Impl().(*Dentry).isDir() {
+		return syserror.ENOTDIR
+	}
+	if inode.HasChildren() {
+		return syserror.ENOTEMPTY
+	}
+	virtfs := rp.VirtualFilesystem()
+	parentDentry := vfsd.Parent().Impl().(*Dentry)
+	parentDentry.dirMu.Lock()
+	defer parentDentry.dirMu.Unlock()
+
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
+		return err
+	}
+	if err := parentDentry.inode.RmDir(ctx, rp.Component(), vfsd); err != nil {
+		virtfs.AbortDeleteDentry(vfsd)
+		return err
+	}
+	virtfs.CommitDeleteDentry(vfsd)
+	return nil
+}
+
+// SetStatAt implements vfs.FilesystemImpl.SetStatAt.
+func (fs *Filesystem) SetStatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetStatOptions) error {
+	fs.mu.RLock()
+	_, inode, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return err
+	}
+	if opts.Stat.Mask == 0 {
+		return nil
+	}
+	return inode.SetStat(ctx, fs.VFSFilesystem(), rp.Credentials(), opts)
+}
+
+// StatAt implements vfs.FilesystemImpl.StatAt.
+func (fs *Filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.StatOptions) (linux.Statx, error) {
+	fs.mu.RLock()
+	_, inode, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return linux.Statx{}, err
+	}
+	return inode.Stat(fs.VFSFilesystem(), opts)
+}
+
+// StatFSAt implements vfs.FilesystemImpl.StatFSAt.
+func (fs *Filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linux.Statfs, error) {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return linux.Statfs{}, err
+	}
+	// TODO: actually implement statfs
+	return linux.Statfs{}, syserror.ENOSYS
+}
+
+// SymlinkAt implements vfs.FilesystemImpl.SymlinkAt.
+func (fs *Filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, target string) error {
+	if rp.Done() {
+		return syserror.EEXIST
+	}
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	parentVFSD, parentInode, err := fs.walkParentDirLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	pc, err := checkCreateLocked(ctx, rp, parentVFSD, parentInode)
+	if err != nil {
+		return err
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	child, err := parentInode.NewSymlink(ctx, pc, target)
+	if err != nil {
+		return err
+	}
+	parentVFSD.Impl().(*Dentry).InsertChild(pc, child)
+	return nil
+}
+
+// UnlinkAt implements vfs.FilesystemImpl.UnlinkAt.
+func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error {
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+	vfsd, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.processDeferredDecRefsLocked()
+	if err != nil {
+		return err
+	}
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	if err := checkDeleteLocked(ctx, rp, vfsd); err != nil {
+		return err
+	}
+	if vfsd.Impl().(*Dentry).isDir() {
+		return syserror.EISDIR
+	}
+	virtfs := rp.VirtualFilesystem()
+	parentDentry := vfsd.Parent().Impl().(*Dentry)
+	parentDentry.dirMu.Lock()
+	defer parentDentry.dirMu.Unlock()
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
+		return err
+	}
+	if err := parentDentry.inode.Unlink(ctx, rp.Component(), vfsd); err != nil {
+		virtfs.AbortDeleteDentry(vfsd)
+		return err
+	}
+	virtfs.CommitDeleteDentry(vfsd)
+	return nil
+}
+
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+func (fs *Filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath) (transport.BoundEndpoint, error) {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return nil, err
+	}
+	return nil, syserror.ECONNREFUSED
+}
+
+// ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
+func (fs *Filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath) ([]string, error) {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return nil, err
+	}
+	// kernfs currently does not support extended attributes.
+	return nil, syserror.ENOTSUP
+}
+
+// GetxattrAt implements vfs.FilesystemImpl.GetxattrAt.
+func (fs *Filesystem) GetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, name string) (string, error) {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return "", err
+	}
+	// kernfs currently does not support extended attributes.
+	return "", syserror.ENOTSUP
+}
+
+// SetxattrAt implements vfs.FilesystemImpl.SetxattrAt.
+func (fs *Filesystem) SetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetxattrOptions) error {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return err
+	}
+	// kernfs currently does not support extended attributes.
+	return syserror.ENOTSUP
+}
+
+// RemovexattrAt implements vfs.FilesystemImpl.RemovexattrAt.
+func (fs *Filesystem) RemovexattrAt(ctx context.Context, rp *vfs.ResolvingPath, name string) error {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return err
+	}
+	// kernfs currently does not support extended attributes.
+	return syserror.ENOTSUP
+}
+
+// PrependPath implements vfs.FilesystemImpl.PrependPath.
+func (fs *Filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDentry, b *fspath.Builder) error {
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+	return vfs.GenericPrependPath(vfsroot, vd, b)
+}
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
new file mode 100755
index 000000000..5c84b10c9
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -0,0 +1,577 @@
+// 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
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// InodeNoopRefCount partially implements the Inode interface, specifically the
+// inodeRefs sub interface. InodeNoopRefCount implements a simple reference
+// count for inodes, performing no extra actions when references are obtained or
+// released. This is suitable for simple file inodes that don't reference any
+// resources.
+type InodeNoopRefCount struct {
+}
+
+// IncRef implements Inode.IncRef.
+func (InodeNoopRefCount) IncRef() {
+}
+
+// DecRef implements Inode.DecRef.
+func (InodeNoopRefCount) DecRef() {
+}
+
+// TryIncRef implements Inode.TryIncRef.
+func (InodeNoopRefCount) TryIncRef() bool {
+	return true
+}
+
+// Destroy implements Inode.Destroy.
+func (InodeNoopRefCount) Destroy() {
+}
+
+// InodeDirectoryNoNewChildren partially implements the Inode interface.
+// InodeDirectoryNoNewChildren represents a directory inode which does not
+// support creation of new children.
+type InodeDirectoryNoNewChildren struct{}
+
+// NewFile implements Inode.NewFile.
+func (InodeDirectoryNoNewChildren) NewFile(context.Context, string, vfs.OpenOptions) (*vfs.Dentry, error) {
+	return nil, syserror.EPERM
+}
+
+// NewDir implements Inode.NewDir.
+func (InodeDirectoryNoNewChildren) NewDir(context.Context, string, vfs.MkdirOptions) (*vfs.Dentry, error) {
+	return nil, syserror.EPERM
+}
+
+// NewLink implements Inode.NewLink.
+func (InodeDirectoryNoNewChildren) NewLink(context.Context, string, Inode) (*vfs.Dentry, error) {
+	return nil, syserror.EPERM
+}
+
+// NewSymlink implements Inode.NewSymlink.
+func (InodeDirectoryNoNewChildren) NewSymlink(context.Context, string, string) (*vfs.Dentry, error) {
+	return nil, syserror.EPERM
+}
+
+// NewNode implements Inode.NewNode.
+func (InodeDirectoryNoNewChildren) NewNode(context.Context, string, vfs.MknodOptions) (*vfs.Dentry, error) {
+	return nil, syserror.EPERM
+}
+
+// InodeNotDirectory partially implements the Inode interface, specifically the
+// inodeDirectory and inodeDynamicDirectory sub interfaces. Inodes that do not
+// represent directories can embed this to provide no-op implementations for
+// directory-related functions.
+type InodeNotDirectory struct {
+}
+
+// HasChildren implements Inode.HasChildren.
+func (InodeNotDirectory) HasChildren() bool {
+	return false
+}
+
+// NewFile implements Inode.NewFile.
+func (InodeNotDirectory) NewFile(context.Context, string, vfs.OpenOptions) (*vfs.Dentry, error) {
+	panic("NewFile called on non-directory inode")
+}
+
+// NewDir implements Inode.NewDir.
+func (InodeNotDirectory) NewDir(context.Context, string, vfs.MkdirOptions) (*vfs.Dentry, error) {
+	panic("NewDir called on non-directory inode")
+}
+
+// NewLink implements Inode.NewLinkink.
+func (InodeNotDirectory) NewLink(context.Context, string, Inode) (*vfs.Dentry, error) {
+	panic("NewLink called on non-directory inode")
+}
+
+// NewSymlink implements Inode.NewSymlink.
+func (InodeNotDirectory) NewSymlink(context.Context, string, string) (*vfs.Dentry, error) {
+	panic("NewSymlink called on non-directory inode")
+}
+
+// NewNode implements Inode.NewNode.
+func (InodeNotDirectory) NewNode(context.Context, string, vfs.MknodOptions) (*vfs.Dentry, error) {
+	panic("NewNode called on non-directory inode")
+}
+
+// Unlink implements Inode.Unlink.
+func (InodeNotDirectory) Unlink(context.Context, string, *vfs.Dentry) error {
+	panic("Unlink called on non-directory inode")
+}
+
+// RmDir implements Inode.RmDir.
+func (InodeNotDirectory) RmDir(context.Context, string, *vfs.Dentry) error {
+	panic("RmDir called on non-directory inode")
+}
+
+// Rename implements Inode.Rename.
+func (InodeNotDirectory) Rename(context.Context, string, string, *vfs.Dentry, *vfs.Dentry) (*vfs.Dentry, error) {
+	panic("Rename called on non-directory inode")
+}
+
+// Lookup implements Inode.Lookup.
+func (InodeNotDirectory) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+	panic("Lookup called on non-directory inode")
+}
+
+// IterDirents implements Inode.IterDirents.
+func (InodeNotDirectory) IterDirents(ctx context.Context, callback vfs.IterDirentsCallback, offset, relOffset int64) (newOffset int64, err error) {
+	panic("IterDirents called on non-directory inode")
+}
+
+// Valid implements Inode.Valid.
+func (InodeNotDirectory) Valid(context.Context) bool {
+	return true
+}
+
+// InodeNoDynamicLookup partially implements the Inode interface, specifically
+// the inodeDynamicLookup sub interface. Directory inodes that do not support
+// dymanic entries (i.e. entries that are not "hashed" into the
+// vfs.Dentry.children) can embed this to provide no-op implementations for
+// functions related to dynamic entries.
+type InodeNoDynamicLookup struct{}
+
+// Lookup implements Inode.Lookup.
+func (InodeNoDynamicLookup) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+	return nil, syserror.ENOENT
+}
+
+// IterDirents implements Inode.IterDirents.
+func (InodeNoDynamicLookup) IterDirents(ctx context.Context, callback vfs.IterDirentsCallback, offset, relOffset int64) (int64, error) {
+	return offset, nil
+}
+
+// Valid implements Inode.Valid.
+func (InodeNoDynamicLookup) Valid(ctx context.Context) bool {
+	return true
+}
+
+// InodeNotSymlink partially implements the Inode interface, specifically the
+// inodeSymlink sub interface. All inodes that are not symlinks may embed this
+// to return the appropriate errors from symlink-related functions.
+type InodeNotSymlink struct{}
+
+// Readlink implements Inode.Readlink.
+func (InodeNotSymlink) Readlink(context.Context) (string, error) {
+	return "", syserror.EINVAL
+}
+
+// InodeAttrs partially implements the Inode interface, specifically the
+// inodeMetadata sub interface. InodeAttrs provides functionality related to
+// inode attributes.
+//
+// Must be initialized by Init prior to first use.
+type InodeAttrs struct {
+	ino   uint64
+	mode  uint32
+	uid   uint32
+	gid   uint32
+	nlink uint32
+}
+
+// Init initializes this InodeAttrs.
+func (a *InodeAttrs) Init(creds *auth.Credentials, ino uint64, mode linux.FileMode) {
+	if mode.FileType() == 0 {
+		panic(fmt.Sprintf("No file type specified in 'mode' for InodeAttrs.Init(): mode=0%o", mode))
+	}
+
+	nlink := uint32(1)
+	if mode.FileType() == linux.ModeDirectory {
+		nlink = 2
+	}
+	atomic.StoreUint64(&a.ino, ino)
+	atomic.StoreUint32(&a.mode, uint32(mode))
+	atomic.StoreUint32(&a.uid, uint32(creds.EffectiveKUID))
+	atomic.StoreUint32(&a.gid, uint32(creds.EffectiveKGID))
+	atomic.StoreUint32(&a.nlink, nlink)
+}
+
+// Mode implements Inode.Mode.
+func (a *InodeAttrs) Mode() linux.FileMode {
+	return linux.FileMode(atomic.LoadUint32(&a.mode))
+}
+
+// Stat partially implements Inode.Stat. Note that this function doesn't provide
+// all the stat fields, and the embedder should consider extending the result
+// with filesystem-specific fields.
+func (a *InodeAttrs) Stat(*vfs.Filesystem, vfs.StatOptions) (linux.Statx, error) {
+	var stat linux.Statx
+	stat.Mask = linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID | linux.STATX_INO | linux.STATX_NLINK
+	stat.Ino = atomic.LoadUint64(&a.ino)
+	stat.Mode = uint16(a.Mode())
+	stat.UID = atomic.LoadUint32(&a.uid)
+	stat.GID = atomic.LoadUint32(&a.gid)
+	stat.Nlink = atomic.LoadUint32(&a.nlink)
+
+	// TODO(gvisor.dev/issue/1193): Implement other stat fields like timestamps.
+
+	return stat, nil
+}
+
+// SetStat implements Inode.SetStat.
+func (a *InodeAttrs) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Credentials, opts vfs.SetStatOptions) error {
+	if opts.Stat.Mask == 0 {
+		return nil
+	}
+	if opts.Stat.Mask&^(linux.STATX_MODE|linux.STATX_UID|linux.STATX_GID) != 0 {
+		return syserror.EPERM
+	}
+	if err := vfs.CheckSetStat(ctx, creds, &opts.Stat, a.Mode(), auth.KUID(atomic.LoadUint32(&a.uid)), auth.KGID(atomic.LoadUint32(&a.gid))); err != nil {
+		return err
+	}
+
+	stat := opts.Stat
+	if stat.Mask&linux.STATX_MODE != 0 {
+		for {
+			old := atomic.LoadUint32(&a.mode)
+			new := old | uint32(stat.Mode & ^uint16(linux.S_IFMT))
+			if swapped := atomic.CompareAndSwapUint32(&a.mode, old, new); swapped {
+				break
+			}
+		}
+	}
+
+	if stat.Mask&linux.STATX_UID != 0 {
+		atomic.StoreUint32(&a.uid, stat.UID)
+	}
+	if stat.Mask&linux.STATX_GID != 0 {
+		atomic.StoreUint32(&a.gid, stat.GID)
+	}
+
+	// Note that not all fields are modifiable. For example, the file type and
+	// inode numbers are immutable after node creation.
+
+	// TODO(gvisor.dev/issue/1193): Implement other stat fields like timestamps.
+
+	return nil
+}
+
+// CheckPermissions implements Inode.CheckPermissions.
+func (a *InodeAttrs) CheckPermissions(_ context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	return vfs.GenericCheckPermissions(
+		creds,
+		ats,
+		a.Mode(),
+		auth.KUID(atomic.LoadUint32(&a.uid)),
+		auth.KGID(atomic.LoadUint32(&a.gid)),
+	)
+}
+
+// IncLinks implements Inode.IncLinks.
+func (a *InodeAttrs) IncLinks(n uint32) {
+	if atomic.AddUint32(&a.nlink, n) <= n {
+		panic("InodeLink.IncLinks called with no existing links")
+	}
+}
+
+// DecLinks implements Inode.DecLinks.
+func (a *InodeAttrs) DecLinks() {
+	if nlink := atomic.AddUint32(&a.nlink, ^uint32(0)); nlink == ^uint32(0) {
+		// Negative overflow
+		panic("Inode.DecLinks called at 0 links")
+	}
+}
+
+type slot struct {
+	Name   string
+	Dentry *vfs.Dentry
+	slotEntry
+}
+
+// OrderedChildrenOptions contains initialization options for OrderedChildren.
+type OrderedChildrenOptions struct {
+	// Writable indicates whether vfs.FilesystemImpl methods implemented by
+	// OrderedChildren may modify the tracked children. This applies to
+	// operations related to rename, unlink and rmdir. If an OrderedChildren is
+	// not writable, these operations all fail with EPERM.
+	Writable bool
+}
+
+// OrderedChildren partially implements the Inode interface. OrderedChildren can
+// be embedded in directory inodes to keep track of the children in the
+// directory, and can then be used to implement a generic directory FD -- see
+// GenericDirectoryFD. OrderedChildren is not compatible with dynamic
+// directories.
+//
+// Must be initialize with Init before first use.
+type OrderedChildren struct {
+	refs.AtomicRefCount
+
+	// Can children be modified by user syscalls? It set to false, interface
+	// methods that would modify the children return EPERM. Immutable.
+	writable bool
+
+	mu    sync.RWMutex
+	order slotList
+	set   map[string]*slot
+}
+
+// Init initializes an OrderedChildren.
+func (o *OrderedChildren) Init(opts OrderedChildrenOptions) {
+	o.writable = opts.Writable
+	o.set = make(map[string]*slot)
+}
+
+// DecRef implements Inode.DecRef.
+func (o *OrderedChildren) DecRef() {
+	o.AtomicRefCount.DecRefWithDestructor(o.Destroy)
+}
+
+// Destroy cleans up resources referenced by this OrderedChildren.
+func (o *OrderedChildren) Destroy() {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	o.order.Reset()
+	o.set = nil
+}
+
+// Populate inserts children into this OrderedChildren, and d's dentry
+// cache. Populate returns the number of directories inserted, which the caller
+// may use to update the link count for the parent directory.
+//
+// Precondition: d.Impl() must be a kernfs Dentry. d must represent a directory
+// inode. children must not contain any conflicting entries already in o.
+func (o *OrderedChildren) Populate(d *Dentry, children map[string]*Dentry) uint32 {
+	var links uint32
+	for name, child := range children {
+		if child.isDir() {
+			links++
+		}
+		if err := o.Insert(name, child.VFSDentry()); err != nil {
+			panic(fmt.Sprintf("Collision when attempting to insert child %q (%+v) into %+v", name, child, d))
+		}
+		d.InsertChild(name, child.VFSDentry())
+	}
+	return links
+}
+
+// HasChildren implements Inode.HasChildren.
+func (o *OrderedChildren) HasChildren() bool {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+	return len(o.set) > 0
+}
+
+// Insert inserts child into o. This ignores the writability of o, as this is
+// not part of the vfs.FilesystemImpl interface, and is a lower-level operation.
+func (o *OrderedChildren) Insert(name string, child *vfs.Dentry) error {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	if _, ok := o.set[name]; ok {
+		return syserror.EEXIST
+	}
+	s := &slot{
+		Name:   name,
+		Dentry: child,
+	}
+	o.order.PushBack(s)
+	o.set[name] = s
+	return nil
+}
+
+// Precondition: caller must hold o.mu for writing.
+func (o *OrderedChildren) removeLocked(name string) {
+	if s, ok := o.set[name]; ok {
+		delete(o.set, name)
+		o.order.Remove(s)
+	}
+}
+
+// Precondition: caller must hold o.mu for writing.
+func (o *OrderedChildren) replaceChildLocked(name string, new *vfs.Dentry) *vfs.Dentry {
+	if s, ok := o.set[name]; ok {
+		// Existing slot with given name, simply replace the dentry.
+		var old *vfs.Dentry
+		old, s.Dentry = s.Dentry, new
+		return old
+	}
+
+	// No existing slot with given name, create and hash new slot.
+	s := &slot{
+		Name:   name,
+		Dentry: new,
+	}
+	o.order.PushBack(s)
+	o.set[name] = s
+	return nil
+}
+
+// Precondition: caller must hold o.mu for reading or writing.
+func (o *OrderedChildren) checkExistingLocked(name string, child *vfs.Dentry) error {
+	s, ok := o.set[name]
+	if !ok {
+		return syserror.ENOENT
+	}
+	if s.Dentry != child {
+		panic(fmt.Sprintf("Dentry hashed into inode doesn't match what vfs thinks! OrderedChild: %+v, vfs: %+v", s.Dentry, child))
+	}
+	return nil
+}
+
+// Unlink implements Inode.Unlink.
+func (o *OrderedChildren) Unlink(ctx context.Context, name string, child *vfs.Dentry) error {
+	if !o.writable {
+		return syserror.EPERM
+	}
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	if err := o.checkExistingLocked(name, child); err != nil {
+		return err
+	}
+	o.removeLocked(name)
+	return nil
+}
+
+// Rmdir implements Inode.Rmdir.
+func (o *OrderedChildren) RmDir(ctx context.Context, name string, child *vfs.Dentry) error {
+	// We're not responsible for checking that child is a directory, that it's
+	// empty, or updating any link counts; so this is the same as unlink.
+	return o.Unlink(ctx, name, child)
+}
+
+type renameAcrossDifferentImplementationsError struct{}
+
+func (renameAcrossDifferentImplementationsError) Error() string {
+	return "rename across inodes with different implementations"
+}
+
+// Rename implements Inode.Rename.
+//
+// Precondition: Rename may only be called across two directory inodes with
+// identical implementations of Rename. Practically, this means filesystems that
+// implement Rename by embedding OrderedChildren for any directory
+// implementation must use OrderedChildren for all directory implementations
+// that will support Rename.
+//
+// Postcondition: reference on any replaced dentry transferred to caller.
+func (o *OrderedChildren) Rename(ctx context.Context, oldname, newname string, child, dstDir *vfs.Dentry) (*vfs.Dentry, error) {
+	dst, ok := dstDir.Impl().(*Dentry).inode.(interface{}).(*OrderedChildren)
+	if !ok {
+		return nil, renameAcrossDifferentImplementationsError{}
+	}
+	if !o.writable || !dst.writable {
+		return nil, syserror.EPERM
+	}
+	// Note: There's a potential deadlock below if concurrent calls to Rename
+	// refer to the same src and dst directories in reverse. We avoid any
+	// ordering issues because the caller is required to serialize concurrent
+	// calls to Rename in accordance with the interface declaration.
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	if dst != o {
+		dst.mu.Lock()
+		defer dst.mu.Unlock()
+	}
+	if err := o.checkExistingLocked(oldname, child); err != nil {
+		return nil, err
+	}
+	replaced := dst.replaceChildLocked(newname, child)
+	return replaced, nil
+}
+
+// nthLocked returns an iterator to the nth child tracked by this object. The
+// iterator is valid until the caller releases o.mu. Returns nil if the
+// requested index falls out of bounds.
+//
+// Preconditon: Caller must hold o.mu for reading.
+func (o *OrderedChildren) nthLocked(i int64) *slot {
+	for it := o.order.Front(); it != nil && i >= 0; it = it.Next() {
+		if i == 0 {
+			return it
+		}
+		i--
+	}
+	return nil
+}
+
+// InodeSymlink partially implements Inode interface for symlinks.
+type InodeSymlink struct {
+	InodeNotDirectory
+}
+
+// Open implements Inode.Open.
+func (InodeSymlink) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	return nil, syserror.ELOOP
+}
+
+// StaticDirectory is a standard implementation of a directory with static
+// contents.
+//
+// +stateify savable
+type StaticDirectory struct {
+	InodeNotSymlink
+	InodeDirectoryNoNewChildren
+	InodeAttrs
+	InodeNoDynamicLookup
+	OrderedChildren
+}
+
+var _ Inode = (*StaticDirectory)(nil)
+
+// NewStaticDir creates a new static directory and returns its dentry.
+func NewStaticDir(creds *auth.Credentials, ino uint64, perm linux.FileMode, children map[string]*Dentry) *Dentry {
+	inode := &StaticDirectory{}
+	inode.Init(creds, ino, perm)
+
+	dentry := &Dentry{}
+	dentry.Init(inode)
+
+	inode.OrderedChildren.Init(OrderedChildrenOptions{})
+	links := inode.OrderedChildren.Populate(dentry, children)
+	inode.IncLinks(links)
+
+	return dentry
+}
+
+// Init initializes StaticDirectory.
+func (s *StaticDirectory) Init(creds *auth.Credentials, ino uint64, perm linux.FileMode) {
+	if perm&^linux.PermissionsMask != 0 {
+		panic(fmt.Sprintf("Only permission mask must be set: %x", perm&linux.PermissionsMask))
+	}
+	s.InodeAttrs.Init(creds, ino, linux.ModeDirectory|perm)
+}
+
+// Open implements kernfs.Inode.
+func (s *StaticDirectory) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &GenericDirectoryFD{}
+	fd.Init(rp.Mount(), vfsd, &s.OrderedChildren, &opts)
+	return fd.VFSFileDescription(), nil
+}
+
+// SetStat implements Inode.SetStat not allowing inode attributes to be changed.
+func (*StaticDirectory) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
+
+// AlwaysValid partially implements kernfs.inodeDynamicLookup.
+type AlwaysValid struct{}
+
+// Valid implements kernfs.inodeDynamicLookup.
+func (*AlwaysValid) Valid(context.Context) bool {
+	return true
+}
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
new file mode 100755
index 000000000..2cefef020
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -0,0 +1,420 @@
+// 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 provides the tools to implement inode-based filesystems.
+// Kernfs has two main features:
+//
+// 1. The Inode interface, which maps VFS2's path-based filesystem operations to
+//    specific filesystem nodes. Kernfs uses the Inode interface to provide a
+//    blanket implementation for the vfs.FilesystemImpl. Kernfs also serves as
+//    the synchronization mechanism for all filesystem operations by holding a
+//    filesystem-wide lock across all operations.
+//
+// 2. Various utility types which provide generic implementations for various
+//    parts of the Inode and vfs.FileDescription interfaces. Client filesystems
+//    based on kernfs can embed the appropriate set of these to avoid having to
+//    reimplement common filesystem operations. See inode_impl_util.go and
+//    fd_impl_util.go.
+//
+// Reference Model:
+//
+// Kernfs dentries represents named pointers to inodes. Dentries and inode have
+// independent lifetimes and reference counts. A child dentry unconditionally
+// holds a reference on its parent directory's dentry. A dentry also holds a
+// reference on the inode it points to. Multiple dentries can point to the same
+// inode (for example, in the case of hardlinks). File descriptors hold a
+// reference to the dentry they're opened on.
+//
+// Dentries are guaranteed to exist while holding Filesystem.mu for
+// reading. Dropping dentries require holding Filesystem.mu for writing. To
+// queue dentries for destruction from a read critical section, see
+// Filesystem.deferDecRef.
+//
+// Lock ordering:
+//
+// kernfs.Filesystem.mu
+//   kernfs.Dentry.dirMu
+//     vfs.VirtualFilesystem.mountMu
+//       vfs.Dentry.mu
+//   kernfs.Filesystem.droppedDentriesMu
+//   (inode implementation locks, if any)
+package kernfs
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// Filesystem mostly implements vfs.FilesystemImpl for a generic in-memory
+// filesystem. Concrete implementations are expected to embed this in their own
+// Filesystem type.
+type Filesystem struct {
+	vfsfs vfs.Filesystem
+
+	droppedDentriesMu sync.Mutex
+
+	// droppedDentries is a list of dentries waiting to be DecRef()ed. This is
+	// used to defer dentry destruction until mu can be acquired for
+	// writing. Protected by droppedDentriesMu.
+	droppedDentries []*vfs.Dentry
+
+	// mu synchronizes the lifetime of Dentries on this filesystem. Holding it
+	// for reading guarantees continued existence of any resolved dentries, but
+	// the dentry tree may be modified.
+	//
+	// Kernfs dentries can only be DecRef()ed while holding mu for writing. For
+	// example:
+	//
+	//   fs.mu.Lock()
+	//   defer fs.mu.Unlock()
+	//   ...
+	//   dentry1.DecRef()
+	//   defer dentry2.DecRef() // Ok, will run before Unlock.
+	//
+	// If discarding dentries in a read context, use Filesystem.deferDecRef. For
+	// example:
+	//
+	//   fs.mu.RLock()
+	//   fs.mu.processDeferredDecRefs()
+	//   defer fs.mu.RUnlock()
+	//   ...
+	//   fs.deferDecRef(dentry)
+	mu sync.RWMutex
+
+	// nextInoMinusOne is used to to allocate inode numbers on this
+	// filesystem. Must be accessed by atomic operations.
+	nextInoMinusOne uint64
+}
+
+// deferDecRef defers dropping a dentry ref until the next call to
+// processDeferredDecRefs{,Locked}. See comment on Filesystem.mu.
+//
+// Precondition: d must not already be pending destruction.
+func (fs *Filesystem) deferDecRef(d *vfs.Dentry) {
+	fs.droppedDentriesMu.Lock()
+	fs.droppedDentries = append(fs.droppedDentries, d)
+	fs.droppedDentriesMu.Unlock()
+}
+
+// processDeferredDecRefs calls vfs.Dentry.DecRef on all dentries in the
+// droppedDentries list. See comment on Filesystem.mu.
+func (fs *Filesystem) processDeferredDecRefs() {
+	fs.mu.Lock()
+	fs.processDeferredDecRefsLocked()
+	fs.mu.Unlock()
+}
+
+// Precondition: fs.mu must be held for writing.
+func (fs *Filesystem) processDeferredDecRefsLocked() {
+	fs.droppedDentriesMu.Lock()
+	for _, d := range fs.droppedDentries {
+		d.DecRef()
+	}
+	fs.droppedDentries = fs.droppedDentries[:0] // Keep slice memory for reuse.
+	fs.droppedDentriesMu.Unlock()
+}
+
+// Init initializes a kernfs filesystem. This should be called from during
+// vfs.FilesystemType.NewFilesystem for the concrete filesystem embedding
+// kernfs.
+func (fs *Filesystem) Init(vfsObj *vfs.VirtualFilesystem, fsType vfs.FilesystemType) {
+	fs.vfsfs.Init(vfsObj, fsType, fs)
+}
+
+// VFSFilesystem returns the generic vfs filesystem object.
+func (fs *Filesystem) VFSFilesystem() *vfs.Filesystem {
+	return &fs.vfsfs
+}
+
+// NextIno allocates a new inode number on this filesystem.
+func (fs *Filesystem) NextIno() uint64 {
+	return atomic.AddUint64(&fs.nextInoMinusOne, 1)
+}
+
+// These consts are used in the Dentry.flags field.
+const (
+	// Dentry points to a directory inode.
+	dflagsIsDir = 1 << iota
+
+	// Dentry points to a symlink inode.
+	dflagsIsSymlink
+)
+
+// Dentry implements vfs.DentryImpl.
+//
+// A kernfs dentry is similar to a dentry in a traditional filesystem: it's a
+// named reference to an inode. A dentry generally lives as long as it's part of
+// a mounted filesystem tree. Kernfs doesn't cache dentries once all references
+// to them are removed. Dentries hold a single reference to the inode they point
+// to, and child dentries hold a reference on their parent.
+//
+// Must be initialized by Init prior to first use.
+type Dentry struct {
+	refs.AtomicRefCount
+
+	vfsd  vfs.Dentry
+	inode Inode
+
+	// flags caches useful information about the dentry from the inode. See the
+	// dflags* consts above. Must be accessed by atomic ops.
+	flags uint32
+
+	// dirMu protects vfsd.children for directory dentries.
+	dirMu sync.Mutex
+}
+
+// Init initializes this dentry.
+//
+// Precondition: Caller must hold a reference on inode.
+//
+// Postcondition: Caller's reference on inode is transferred to the dentry.
+func (d *Dentry) Init(inode Inode) {
+	d.vfsd.Init(d)
+	d.inode = inode
+	ftype := inode.Mode().FileType()
+	if ftype == linux.ModeDirectory {
+		d.flags |= dflagsIsDir
+	}
+	if ftype == linux.ModeSymlink {
+		d.flags |= dflagsIsSymlink
+	}
+}
+
+// VFSDentry returns the generic vfs dentry for this kernfs dentry.
+func (d *Dentry) VFSDentry() *vfs.Dentry {
+	return &d.vfsd
+}
+
+// isDir checks whether the dentry points to a directory inode.
+func (d *Dentry) isDir() bool {
+	return atomic.LoadUint32(&d.flags)&dflagsIsDir != 0
+}
+
+// isSymlink checks whether the dentry points to a symlink inode.
+func (d *Dentry) isSymlink() bool {
+	return atomic.LoadUint32(&d.flags)&dflagsIsSymlink != 0
+}
+
+// DecRef implements vfs.DentryImpl.DecRef.
+func (d *Dentry) DecRef() {
+	d.AtomicRefCount.DecRefWithDestructor(d.destroy)
+}
+
+// Precondition: Dentry must be removed from VFS' dentry cache.
+func (d *Dentry) destroy() {
+	d.inode.DecRef() // IncRef from Init.
+	d.inode = nil
+	if parent := d.vfsd.Parent(); parent != nil {
+		parent.DecRef() // IncRef from Dentry.InsertChild.
+	}
+}
+
+// InsertChild inserts child into the vfs dentry cache with the given name under
+// this dentry. This does not update the directory inode, so calling this on
+// it's own isn't sufficient to insert a child into a directory. InsertChild
+// updates the link count on d if required.
+//
+// Precondition: d must represent a directory inode.
+func (d *Dentry) InsertChild(name string, child *vfs.Dentry) {
+	d.dirMu.Lock()
+	d.insertChildLocked(name, child)
+	d.dirMu.Unlock()
+}
+
+// insertChildLocked is equivalent to InsertChild, with additional
+// preconditions.
+//
+// Precondition: d.dirMu must be locked.
+func (d *Dentry) insertChildLocked(name string, child *vfs.Dentry) {
+	if !d.isDir() {
+		panic(fmt.Sprintf("InsertChild called on non-directory Dentry: %+v.", d))
+	}
+	vfsDentry := d.VFSDentry()
+	vfsDentry.IncRef() // DecRef in child's Dentry.destroy.
+	vfsDentry.InsertChild(child, name)
+}
+
+// The Inode interface maps filesystem-level operations that operate on paths to
+// equivalent operations on specific filesystem nodes.
+//
+// The interface methods are groups into logical categories as sub interfaces
+// below. Generally, an implementation for each sub interface can be provided by
+// embedding an appropriate type from inode_impl_utils.go. The sub interfaces
+// are purely organizational. Methods declared directly in the main interface
+// have no generic implementations, and should be explicitly provided by the
+// client filesystem.
+//
+// Generally, implementations are not responsible for tasks that are common to
+// all filesystems. These include:
+//
+// - Checking that dentries passed to methods are of the appropriate file type.
+// - Checking permissions.
+// - Updating link and reference counts.
+//
+// Specific responsibilities of implementations are documented below.
+type Inode interface {
+	// Methods related to reference counting. A generic implementation is
+	// provided by InodeNoopRefCount. These methods are generally called by the
+	// equivalent Dentry methods.
+	inodeRefs
+
+	// Methods related to node metadata. A generic implementation is provided by
+	// InodeAttrs.
+	inodeMetadata
+
+	// Method for inodes that represent symlink. InodeNotSymlink provides a
+	// blanket implementation for all non-symlink inodes.
+	inodeSymlink
+
+	// Method for inodes that represent directories. InodeNotDirectory provides
+	// a blanket implementation for all non-directory inodes.
+	inodeDirectory
+
+	// Method for inodes that represent dynamic directories and their
+	// children. InodeNoDynamicLookup provides a blanket implementation for all
+	// non-dynamic-directory inodes.
+	inodeDynamicLookup
+
+	// Open creates a file description for the filesystem object represented by
+	// this inode. The returned file description should hold a reference on the
+	// inode for its lifetime.
+	//
+	// Precondition: rp.Done(). vfsd.Impl() must be the kernfs Dentry containing
+	// the inode on which Open() is being called.
+	Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error)
+}
+
+type inodeRefs interface {
+	IncRef()
+	DecRef()
+	TryIncRef() bool
+	// Destroy is called when the inode reaches zero references. Destroy release
+	// all resources (references) on objects referenced by the inode, including
+	// any child dentries.
+	Destroy()
+}
+
+type inodeMetadata interface {
+	// CheckPermissions checks that creds may access this inode for the
+	// requested access type, per the the rules of
+	// fs/namei.c:generic_permission().
+	CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error
+
+	// Mode returns the (struct stat)::st_mode value for this inode. This is
+	// separated from Stat for performance.
+	Mode() linux.FileMode
+
+	// Stat returns the metadata for this inode. This corresponds to
+	// vfs.FilesystemImpl.StatAt.
+	Stat(fs *vfs.Filesystem, opts vfs.StatOptions) (linux.Statx, error)
+
+	// SetStat updates the metadata for this inode. This corresponds to
+	// vfs.FilesystemImpl.SetStatAt. Implementations are responsible for checking
+	// if the operation can be performed (see vfs.CheckSetStat() for common
+	// checks).
+	SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Credentials, opts vfs.SetStatOptions) error
+}
+
+// Precondition: All methods in this interface may only be called on directory
+// inodes.
+type inodeDirectory interface {
+	// The New{File,Dir,Node,Symlink} methods below should return a new inode
+	// hashed into this inode.
+	//
+	// These inode constructors are inode-level operations rather than
+	// filesystem-level operations to allow client filesystems to mix different
+	// implementations based on the new node's location in the
+	// filesystem.
+
+	// HasChildren returns true if the directory inode has any children.
+	HasChildren() bool
+
+	// NewFile creates a new regular file inode.
+	NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (*vfs.Dentry, error)
+
+	// NewDir creates a new directory inode.
+	NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error)
+
+	// NewLink creates a new hardlink to a specified inode in this
+	// directory. Implementations should create a new kernfs Dentry pointing to
+	// target, and update target's link count.
+	NewLink(ctx context.Context, name string, target Inode) (*vfs.Dentry, error)
+
+	// NewSymlink creates a new symbolic link inode.
+	NewSymlink(ctx context.Context, name, target string) (*vfs.Dentry, error)
+
+	// NewNode creates a new filesystem node for a mknod syscall.
+	NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (*vfs.Dentry, error)
+
+	// Unlink removes a child dentry from this directory inode.
+	Unlink(ctx context.Context, name string, child *vfs.Dentry) error
+
+	// RmDir removes an empty child directory from this directory
+	// inode. Implementations must update the parent directory's link count,
+	// if required. Implementations are not responsible for checking that child
+	// is a directory, checking for an empty directory.
+	RmDir(ctx context.Context, name string, child *vfs.Dentry) error
+
+	// Rename is called on the source directory containing an inode being
+	// renamed. child should point to the resolved child in the source
+	// directory. If Rename replaces a dentry in the destination directory, it
+	// should return the replaced dentry or nil otherwise.
+	//
+	// Precondition: Caller must serialize concurrent calls to Rename.
+	Rename(ctx context.Context, oldname, newname string, child, dstDir *vfs.Dentry) (replaced *vfs.Dentry, err error)
+}
+
+type inodeDynamicLookup interface {
+	// Lookup should return an appropriate dentry if name should resolve to a
+	// child of this dynamic directory inode. This gives the directory an
+	// opportunity on every lookup to resolve additional entries that aren't
+	// hashed into the directory. This is only called when the inode is a
+	// directory. If the inode is not a directory, or if the directory only
+	// contains a static set of children, the implementer can unconditionally
+	// return an appropriate error (ENOTDIR and ENOENT respectively).
+	//
+	// The child returned by Lookup will be hashed into the VFS dentry tree. Its
+	// lifetime can be controlled by the filesystem implementation with an
+	// appropriate implementation of Valid.
+	//
+	// Lookup returns the child with an extra reference and the caller owns this
+	// reference.
+	Lookup(ctx context.Context, name string) (*vfs.Dentry, error)
+
+	// Valid should return true if this inode is still valid, or needs to
+	// be resolved again by a call to Lookup.
+	Valid(ctx context.Context) bool
+
+	// IterDirents is used to iterate over dynamically created entries. It invokes
+	// cb on each entry in the directory represented by the FileDescription.
+	// 'offset' is the offset for the entire IterDirents call, which may include
+	// results from the caller. 'relOffset' is the offset inside the entries
+	// returned by this IterDirents invocation. In other words,
+	// 'offset+relOffset+1' is the value that should be set in vfs.Dirent.NextOff,
+	// while 'relOffset' is the place where iteration should start from.
+	IterDirents(ctx context.Context, callback vfs.IterDirentsCallback, offset, relOffset int64) (newOffset int64, err error)
+}
+
+type inodeSymlink interface {
+	// Readlink resolves the target of a symbolic link. If an inode is not a
+	// symlink, the implementation should return EINVAL.
+	Readlink(ctx context.Context) (string, error)
+}
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/slot_list.go b/pkg/sentry/fsimpl/kernfs/slot_list.go
new file mode 100755
index 000000000..5c8020e11
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/slot_list.go
@@ -0,0 +1,186 @@
+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
+}
+
+// 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
new file mode 100755
index 000000000..5918d3309
--- /dev/null
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
@@ -0,0 +1,61 @@
+// 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
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// StaticSymlink provides an Inode implementation for symlinks that point to
+// a immutable target.
+type StaticSymlink struct {
+	InodeAttrs
+	InodeNoopRefCount
+	InodeSymlink
+
+	target string
+}
+
+var _ Inode = (*StaticSymlink)(nil)
+
+// NewStaticSymlink creates a new symlink file pointing to 'target'.
+func NewStaticSymlink(creds *auth.Credentials, ino uint64, target string) *Dentry {
+	inode := &StaticSymlink{}
+	inode.Init(creds, ino, target)
+
+	d := &Dentry{}
+	d.Init(inode)
+	return d
+}
+
+// Init initializes the instance.
+func (s *StaticSymlink) Init(creds *auth.Credentials, ino uint64, target string) {
+	s.target = target
+	s.InodeAttrs.Init(creds, ino, linux.ModeSymlink|0777)
+}
+
+// Readlink implements Inode.
+func (s *StaticSymlink) Readlink(_ context.Context) (string, error) {
+	return s.target, nil
+}
+
+// SetStat implements Inode.SetStat not allowing inode attributes to be changed.
+func (*StaticSymlink) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
new file mode 100755
index 000000000..c13511de2
--- /dev/null
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -0,0 +1,73 @@
+// Copyright 2020 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 sockfs provides a filesystem implementation for anonymous sockets.
+package sockfs
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// NewFilesystem creates a new sockfs filesystem.
+//
+// Note that there should only ever be one instance of sockfs.Filesystem,
+// backing a global socket mount.
+func NewFilesystem(vfsObj *vfs.VirtualFilesystem) *vfs.Filesystem {
+	fs, _, err := filesystemType{}.GetFilesystem(nil, vfsObj, nil, "", vfs.GetFilesystemOptions{})
+	if err != nil {
+		panic("failed to create sockfs filesystem")
+	}
+	return fs
+}
+
+// filesystemType implements vfs.FilesystemType.
+type filesystemType struct{}
+
+// GetFilesystem implements FilesystemType.GetFilesystem.
+func (fsType filesystemType) GetFilesystem(_ context.Context, vfsObj *vfs.VirtualFilesystem, _ *auth.Credentials, _ string, _ vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	fs := &filesystem{}
+	fs.Init(vfsObj, fsType)
+	return fs.VFSFilesystem(), nil, nil
+}
+
+// Name implements FilesystemType.Name.
+//
+// Note that registering sockfs is unnecessary, except for the fact that it
+// will not show up under /proc/filesystems as a result. This is a very minor
+// discrepancy from Linux.
+func (filesystemType) Name() string {
+	return "sockfs"
+}
+
+// filesystem implements vfs.FilesystemImpl.
+type filesystem struct {
+	kernfs.Filesystem
+}
+
+// inode implements kernfs.Inode.
+type inode struct {
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+	kernfs.InodeAttrs
+	kernfs.InodeNoopRefCount
+}
+
+// Open implements kernfs.Inode.Open.
+func (i *inode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	return nil, syserror.ENXIO
+}
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go b/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go
new file mode 100755
index 000000000..8d5b85e2c
--- /dev/null
+++ b/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go
@@ -0,0 +1,3 @@
+// automatically generated by stateify.
+
+package sockfs
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 6feda8fa1..0a448b57c 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -50,6 +50,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/timerfd"
 	"gvisor.dev/gvisor/pkg/sentry/fsbridge"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/sockfs"
 	"gvisor.dev/gvisor/pkg/sentry/hostcpu"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -225,6 +226,11 @@ type Kernel struct {
 	// by extMu.
 	nextSocketEntry uint64
 
+	// socketMount is a disconnected vfs.Mount, not included in k.vfs,
+	// representing a sockfs.filesystem. socketMount is used to back
+	// VirtualDentries representing anonymous sockets.
+	socketMount *vfs.Mount
+
 	// deviceRegistry is used to save/restore device.SimpleDevices.
 	deviceRegistry struct{} `state:".(*device.Registry)"`
 
@@ -348,6 +354,19 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 	k.monotonicClock = &timekeeperClock{tk: args.Timekeeper, c: sentrytime.Monotonic}
 	k.futexes = futex.NewManager()
 	k.netlinkPorts = port.New()
+	if VFS2Enabled {
+		if err := k.vfs.Init(); err != nil {
+			return fmt.Errorf("failed to initialize VFS: %v", err)
+		}
+		fs := sockfs.NewFilesystem(&k.vfs)
+		// NewDisconnectedMount will take an additional reference on fs.
+		defer fs.DecRef()
+		sm, err := k.vfs.NewDisconnectedMount(fs, nil, &vfs.MountOptions{})
+		if err != nil {
+			return fmt.Errorf("failed to initialize socket mount: %v", err)
+		}
+		k.socketMount = sm
+	}
 	return nil
 }
 
@@ -1452,6 +1471,11 @@ func (k *Kernel) ListSockets() []*SocketEntry {
 	return socks
 }
 
+// SocketMount returns the global socket mount.
+func (k *Kernel) SocketMount() *vfs.Mount {
+	return k.socketMount
+}
+
 // supervisorContext is a privileged context.
 type supervisorContext struct {
 	context.NoopSleeper
diff --git a/pkg/sentry/kernel/kernel_state_autogen.go b/pkg/sentry/kernel/kernel_state_autogen.go
index 57a261086..9c39a9108 100755
--- a/pkg/sentry/kernel/kernel_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_state_autogen.go
@@ -155,6 +155,7 @@ func (x *Kernel) save(m state.Map) {
 	m.Save("netlinkPorts", &x.netlinkPorts)
 	m.Save("sockets", &x.sockets)
 	m.Save("nextSocketEntry", &x.nextSocketEntry)
+	m.Save("socketMount", &x.socketMount)
 	m.Save("DirentCacheLimiter", &x.DirentCacheLimiter)
 	m.Save("SpecialOpts", &x.SpecialOpts)
 	m.Save("vfs", &x.vfs)
@@ -190,6 +191,7 @@ func (x *Kernel) load(m state.Map) {
 	m.Load("netlinkPorts", &x.netlinkPorts)
 	m.Load("sockets", &x.sockets)
 	m.Load("nextSocketEntry", &x.nextSocketEntry)
+	m.Load("socketMount", &x.socketMount)
 	m.Load("DirentCacheLimiter", &x.DirentCacheLimiter)
 	m.Load("SpecialOpts", &x.SpecialOpts)
 	m.Load("vfs", &x.vfs)