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diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
new file mode 100755
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+++ b/pkg/sentry/vfs/vfs.go
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+// 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 vfs implements a virtual filesystem layer.
+//
+// Lock order:
+//
+// Filesystem implementation locks
+//   VirtualFilesystem.mountMu
+// VirtualFilesystem.fsTypesMu
+package vfs
+
+import (
+	"sync"
+)
+
+// A VirtualFilesystem (VFS for short) combines Filesystems in trees of Mounts.
+//
+// There is no analogue to the VirtualFilesystem type in Linux, as the
+// equivalent state in Linux is global.
+type VirtualFilesystem struct {
+	// mountMu serializes mount mutations.
+	//
+	// mountMu is analogous to Linux's namespace_sem.
+	mountMu sync.RWMutex
+
+	// mounts maps (mount parent, mount point) pairs to mounts. (Since mounts
+	// are uniquely namespaced, including mount parent in the key correctly
+	// handles both bind mounts and mount namespaces; Linux does the same.)
+	// Synchronization between mutators and readers is provided by mounts.seq;
+	// synchronization between mutators is provided by mountMu.
+	//
+	// mounts is used to follow mount points during path traversal. We use a
+	// single table rather than per-Dentry tables to reduce size (and therefore
+	// cache footprint) for the vast majority of Dentries that are not mount
+	// points.
+	//
+	// mounts is analogous to Linux's mount_hashtable.
+	mounts mountTable
+
+	// mountpoints maps mount points to mounts at those points in all
+	// namespaces. mountpoints is protected by mountMu.
+	//
+	// mountpoints is used to find mounts that must be unmounted due to
+	// removal of a mount point Dentry from another mount namespace. ("A file
+	// or directory that is a mount point in one namespace that is not a mount
+	// point in another namespace, may be renamed, unlinked, or removed
+	// (rmdir(2)) in the mount namespace in which it is not a mount point
+	// (subject to the usual permission checks)." - mount_namespaces(7))
+	//
+	// mountpoints is analogous to Linux's mountpoint_hashtable.
+	mountpoints map[*Dentry]map[*Mount]struct{}
+
+	// fsTypes contains all FilesystemTypes that are usable in the
+	// VirtualFilesystem. fsTypes is protected by fsTypesMu.
+	fsTypesMu sync.RWMutex
+	fsTypes   map[string]FilesystemType
+}
+
+// New returns a new VirtualFilesystem with no mounts or FilesystemTypes.
+func New() *VirtualFilesystem {
+	vfs := &VirtualFilesystem{
+		mountpoints: make(map[*Dentry]map[*Mount]struct{}),
+		fsTypes:     make(map[string]FilesystemType),
+	}
+	vfs.mounts.Init()
+	return vfs
+}
+
+// A VirtualDentry represents a node in a VFS tree, by combining a Dentry
+// (which represents a node in a Filesystem's tree) and a Mount (which
+// represents the Filesystem's position in a VFS mount tree).
+//
+// VirtualDentry's semantics are similar to that of a Go interface object
+// representing a pointer: it is a copyable value type that represents
+// references to another entity. The zero value of VirtualDentry is an "empty
+// VirtualDentry", directly analogous to a nil interface object.
+// VirtualDentry.Ok() checks that a VirtualDentry is not zero-valued; unless
+// otherwise specified, all other VirtualDentry methods require
+// VirtualDentry.Ok() == true.
+//
+// Mounts and Dentries are reference-counted, requiring that users call
+// VirtualDentry.{Inc,Dec}Ref() as appropriate. We often colloquially refer to
+// references on the Mount and Dentry referred to by a VirtualDentry as
+// references on the VirtualDentry itself. Unless otherwise specified, all
+// VirtualDentry methods require that a reference is held on the VirtualDentry.
+//
+// VirtualDentry is analogous to Linux's struct path.
+type VirtualDentry struct {
+	mount  *Mount
+	dentry *Dentry
+}
+
+// Ok returns true if vd is not empty. It does not require that a reference is
+// held.
+func (vd VirtualDentry) Ok() bool {
+	return vd.mount != nil
+}
+
+// IncRef increments the reference counts on the Mount and Dentry represented
+// by vd.
+func (vd VirtualDentry) IncRef() {
+	vd.mount.incRef()
+	vd.dentry.incRef(vd.mount.fs)
+}
+
+// DecRef decrements the reference counts on the Mount and Dentry represented
+// by vd.
+func (vd VirtualDentry) DecRef() {
+	vd.dentry.decRef(vd.mount.fs)
+	vd.mount.decRef()
+}
+
+// Mount returns the Mount associated with vd. It does not take a reference on
+// the returned Mount.
+func (vd VirtualDentry) Mount() *Mount {
+	return vd.mount
+}
+
+// Dentry returns the Dentry associated with vd. It does not take a reference
+// on the returned Dentry.
+func (vd VirtualDentry) Dentry() *Dentry {
+	return vd.dentry
+}