Convert memfs into proto-tmpfs.

- Renamed memfs to tmpfs.
- Copied fileRangeSet bits from fs/fsutil/ to fsimpl/tmpfs/
- Changed tmpfs to be backed by filemem instead of byte slice.
- regularFileReadWriter uses a sync.Pool, similar to gofer client.

PiperOrigin-RevId: 288356380

13 files changed, 653 insertions, 208 deletions

diff --git a/pkg/sentry/fs/fsutil/BUILD b/pkg/sentry/fs/fsutil/BUILD
index b2e8d9c77..9ca695a95 100644
--- a/pkg/sentry/fs/fsutil/BUILD
+++ b/pkg/sentry/fs/fsutil/BUILD
@@ -53,7 +53,7 @@ go_template_instance(
         "Key": "uint64",
         "Range": "memmap.MappableRange",
         "Value": "uint64",
-        "Functions": "fileRangeSetFunctions",
+        "Functions": "FileRangeSetFunctions",
     },
 )
 
diff --git a/pkg/sentry/fs/fsutil/file_range_set.go b/pkg/sentry/fs/fsutil/file_range_set.go
index 0a5466b0a..f52d712e3 100644
--- a/pkg/sentry/fs/fsutil/file_range_set.go
+++ b/pkg/sentry/fs/fsutil/file_range_set.go
@@ -34,25 +34,25 @@ import (
 //
 // type FileRangeSet <generated by go_generics>
 
-// fileRangeSetFunctions implements segment.Functions for FileRangeSet.
-type fileRangeSetFunctions struct{}
+// FileRangeSetFunctions implements segment.Functions for FileRangeSet.
+type FileRangeSetFunctions struct{}
 
 // MinKey implements segment.Functions.MinKey.
-func (fileRangeSetFunctions) MinKey() uint64 {
+func (FileRangeSetFunctions) MinKey() uint64 {
 	return 0
 }
 
 // MaxKey implements segment.Functions.MaxKey.
-func (fileRangeSetFunctions) MaxKey() uint64 {
+func (FileRangeSetFunctions) MaxKey() uint64 {
 	return math.MaxUint64
 }
 
 // ClearValue implements segment.Functions.ClearValue.
-func (fileRangeSetFunctions) ClearValue(_ *uint64) {
+func (FileRangeSetFunctions) ClearValue(_ *uint64) {
 }
 
 // Merge implements segment.Functions.Merge.
-func (fileRangeSetFunctions) Merge(mr1 memmap.MappableRange, frstart1 uint64, _ memmap.MappableRange, frstart2 uint64) (uint64, bool) {
+func (FileRangeSetFunctions) Merge(mr1 memmap.MappableRange, frstart1 uint64, _ memmap.MappableRange, frstart2 uint64) (uint64, bool) {
 	if frstart1+mr1.Length() != frstart2 {
 		return 0, false
 	}
@@ -60,7 +60,7 @@ func (fileRangeSetFunctions) Merge(mr1 memmap.MappableRange, frstart1 uint64, _
 }
 
 // Split implements segment.Functions.Split.
-func (fileRangeSetFunctions) Split(mr memmap.MappableRange, frstart uint64, split uint64) (uint64, uint64) {
+func (FileRangeSetFunctions) Split(mr memmap.MappableRange, frstart uint64, split uint64) (uint64, uint64) {
 	return frstart, frstart + (split - mr.Start)
 }
 
diff --git a/pkg/sentry/fsimpl/memfs/regular_file.go b/pkg/sentry/fsimpl/memfs/regular_file.go
deleted file mode 100644
index b7f4853b3..000000000
--- a/pkg/sentry/fsimpl/memfs/regular_file.go
+++ /dev/null
@@ -1,154 +0,0 @@
-// Copyright 2019 The gVisor Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package memfs
-
-import (
-	"io"
-	"sync"
-	"sync/atomic"
-
-	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/sentry/context"
-	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
-	"gvisor.dev/gvisor/pkg/sentry/usermem"
-	"gvisor.dev/gvisor/pkg/sentry/vfs"
-	"gvisor.dev/gvisor/pkg/syserror"
-)
-
-type regularFile struct {
-	inode inode
-
-	mu   sync.RWMutex
-	data []byte
-	// dataLen is len(data), but accessed using atomic memory operations to
-	// avoid locking in inode.stat().
-	dataLen int64
-}
-
-func (fs *filesystem) newRegularFile(creds *auth.Credentials, mode linux.FileMode) *inode {
-	file := &regularFile{}
-	file.inode.init(file, fs, creds, mode)
-	file.inode.nlink = 1 // from parent directory
-	return &file.inode
-}
-
-type regularFileFD struct {
-	fileDescription
-
-	// These are immutable.
-	readable bool
-	writable bool
-
-	// off is the file offset. off is accessed using atomic memory operations.
-	// offMu serializes operations that may mutate off.
-	off   int64
-	offMu sync.Mutex
-}
-
-// Release implements vfs.FileDescriptionImpl.Release.
-func (fd *regularFileFD) Release() {
-	if fd.writable {
-		fd.vfsfd.VirtualDentry().Mount().EndWrite()
-	}
-}
-
-// PRead implements vfs.FileDescriptionImpl.PRead.
-func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
-	if !fd.readable {
-		return 0, syserror.EINVAL
-	}
-	f := fd.inode().impl.(*regularFile)
-	f.mu.RLock()
-	if offset >= int64(len(f.data)) {
-		f.mu.RUnlock()
-		return 0, io.EOF
-	}
-	n, err := dst.CopyOut(ctx, f.data[offset:])
-	f.mu.RUnlock()
-	return int64(n), err
-}
-
-// Read implements vfs.FileDescriptionImpl.Read.
-func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
-	fd.offMu.Lock()
-	n, err := fd.PRead(ctx, dst, fd.off, opts)
-	fd.off += n
-	fd.offMu.Unlock()
-	return n, err
-}
-
-// PWrite implements vfs.FileDescriptionImpl.PWrite.
-func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
-	if !fd.writable {
-		return 0, syserror.EINVAL
-	}
-	if offset < 0 {
-		return 0, syserror.EINVAL
-	}
-	srclen := src.NumBytes()
-	if srclen == 0 {
-		return 0, nil
-	}
-	f := fd.inode().impl.(*regularFile)
-	f.mu.Lock()
-	end := offset + srclen
-	if end < offset {
-		// Overflow.
-		f.mu.Unlock()
-		return 0, syserror.EFBIG
-	}
-	if end > f.dataLen {
-		f.data = append(f.data, make([]byte, end-f.dataLen)...)
-		atomic.StoreInt64(&f.dataLen, end)
-	}
-	n, err := src.CopyIn(ctx, f.data[offset:end])
-	f.mu.Unlock()
-	return int64(n), err
-}
-
-// Write implements vfs.FileDescriptionImpl.Write.
-func (fd *regularFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
-	fd.offMu.Lock()
-	n, err := fd.PWrite(ctx, src, fd.off, opts)
-	fd.off += n
-	fd.offMu.Unlock()
-	return n, err
-}
-
-// Seek implements vfs.FileDescriptionImpl.Seek.
-func (fd *regularFileFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
-	fd.offMu.Lock()
-	defer fd.offMu.Unlock()
-	switch whence {
-	case linux.SEEK_SET:
-		// use offset as specified
-	case linux.SEEK_CUR:
-		offset += fd.off
-	case linux.SEEK_END:
-		offset += atomic.LoadInt64(&fd.inode().impl.(*regularFile).dataLen)
-	default:
-		return 0, syserror.EINVAL
-	}
-	if offset < 0 {
-		return 0, syserror.EINVAL
-	}
-	fd.off = offset
-	return offset, nil
-}
-
-// Sync implements vfs.FileDescriptionImpl.Sync.
-func (fd *regularFileFD) Sync(ctx context.Context) error {
-	return nil
-}
diff --git a/pkg/sentry/fsimpl/memfs/BUILD b/pkg/sentry/fsimpl/tmpfs/BUILD
index 5689bed3b..a5b285987 100644
--- a/pkg/sentry/fsimpl/memfs/BUILD
+++ b/pkg/sentry/fsimpl/tmpfs/BUILD
@@ -1,14 +1,13 @@
 load("//tools/go_stateify:defs.bzl", "go_library")
 load("@io_bazel_rules_go//go:def.bzl", "go_test")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
 
 package(licenses = ["notice"])
 
-load("//tools/go_generics:defs.bzl", "go_template_instance")
-
 go_template_instance(
     name = "dentry_list",
     out = "dentry_list.go",
-    package = "memfs",
+    package = "tmpfs",
     prefix = "dentry",
     template = "//pkg/ilist:generic_list",
     types = {
@@ -18,25 +17,34 @@ go_template_instance(
 )
 
 go_library(
-    name = "memfs",
+    name = "tmpfs",
     srcs = [
         "dentry_list.go",
         "directory.go",
         "filesystem.go",
-        "memfs.go",
         "named_pipe.go",
         "regular_file.go",
         "symlink.go",
+        "tmpfs.go",
     ],
-    importpath = "gvisor.dev/gvisor/pkg/sentry/fsimpl/memfs",
+    importpath = "gvisor.dev/gvisor/pkg/sentry/fsimpl/tmpfs",
     deps = [
         "//pkg/abi/linux",
         "//pkg/amutex",
         "//pkg/fspath",
+        "//pkg/log",
         "//pkg/sentry/arch",
         "//pkg/sentry/context",
+        "//pkg/sentry/fs",
+        "//pkg/sentry/fs/fsutil",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/pipe",
+        "//pkg/sentry/memmap",
+        "//pkg/sentry/pgalloc",
+        "//pkg/sentry/platform",
+        "//pkg/sentry/safemem",
+        "//pkg/sentry/usage",
         "//pkg/sentry/usermem",
         "//pkg/sentry/vfs",
         "//pkg/syserror",
@@ -48,7 +56,7 @@ go_test(
     size = "small",
     srcs = ["benchmark_test.go"],
     deps = [
-        ":memfs",
+        ":tmpfs",
         "//pkg/abi/linux",
         "//pkg/fspath",
         "//pkg/refs",
@@ -63,16 +71,20 @@ go_test(
 )
 
 go_test(
-    name = "memfs_test",
+    name = "tmpfs_test",
     size = "small",
-    srcs = ["pipe_test.go"],
-    embed = [":memfs"],
+    srcs = [
+        "pipe_test.go",
+        "regular_file_test.go",
+    ],
+    embed = [":tmpfs"],
     deps = [
         "//pkg/abi/linux",
         "//pkg/fspath",
         "//pkg/sentry/context",
         "//pkg/sentry/context/contexttest",
         "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/contexttest",
         "//pkg/sentry/usermem",
         "//pkg/sentry/vfs",
         "//pkg/syserror",
diff --git a/pkg/sentry/fsimpl/memfs/benchmark_test.go b/pkg/sentry/fsimpl/tmpfs/benchmark_test.go
index a27876a4e..d88c83499 100644
--- a/pkg/sentry/fsimpl/memfs/benchmark_test.go
+++ b/pkg/sentry/fsimpl/tmpfs/benchmark_test.go
@@ -27,7 +27,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	_ "gvisor.dev/gvisor/pkg/sentry/fs/tmpfs"
-	"gvisor.dev/gvisor/pkg/sentry/fsimpl/memfs"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/tmpfs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -176,10 +176,10 @@ func BenchmarkVFS2MemfsStat(b *testing.B) {
 
 			// Create VFS.
 			vfsObj := vfs.New()
-			vfsObj.MustRegisterFilesystemType("memfs", memfs.FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
+			vfsObj.MustRegisterFilesystemType("tmpfs", tmpfs.FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
 				AllowUserMount: true,
 			})
-			mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "memfs", &vfs.GetFilesystemOptions{})
+			mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "tmpfs", &vfs.GetFilesystemOptions{})
 			if err != nil {
 				b.Fatalf("failed to create tmpfs root mount: %v", err)
 			}
@@ -367,10 +367,10 @@ func BenchmarkVFS2MemfsMountStat(b *testing.B) {
 
 			// Create VFS.
 			vfsObj := vfs.New()
-			vfsObj.MustRegisterFilesystemType("memfs", memfs.FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
+			vfsObj.MustRegisterFilesystemType("tmpfs", tmpfs.FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
 				AllowUserMount: true,
 			})
-			mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "memfs", &vfs.GetFilesystemOptions{})
+			mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "tmpfs", &vfs.GetFilesystemOptions{})
 			if err != nil {
 				b.Fatalf("failed to create tmpfs root mount: %v", err)
 			}
@@ -399,7 +399,7 @@ func BenchmarkVFS2MemfsMountStat(b *testing.B) {
 			}
 			defer mountPoint.DecRef()
 			// Create and mount the submount.
-			if err := vfsObj.MountAt(ctx, creds, "", &pop, "memfs", &vfs.MountOptions{}); err != nil {
+			if err := vfsObj.MountAt(ctx, creds, "", &pop, "tmpfs", &vfs.MountOptions{}); err != nil {
 				b.Fatalf("failed to mount tmpfs submount: %v", err)
 			}
 			filePathBuilder.WriteString(mountPointName)
diff --git a/pkg/sentry/fsimpl/memfs/directory.go b/pkg/sentry/fsimpl/tmpfs/directory.go
index 0bd82e480..887ca2619 100644
--- a/pkg/sentry/fsimpl/memfs/directory.go
+++ b/pkg/sentry/fsimpl/tmpfs/directory.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package memfs
+package tmpfs
 
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
diff --git a/pkg/sentry/fsimpl/memfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index b063e09a3..26979729e 100644
--- a/pkg/sentry/fsimpl/memfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package memfs
+package tmpfs
 
 import (
 	"fmt"
@@ -50,7 +50,7 @@ afterSymlink:
 		return nil, err
 	}
 	if nextVFSD == nil {
-		// Since the Dentry tree is the sole source of truth for memfs, if it's
+		// Since the Dentry tree is the sole source of truth for tmpfs, if it's
 		// not in the Dentry tree, it doesn't exist.
 		return nil, syserror.ENOENT
 	}
@@ -351,8 +351,8 @@ func (d *dentry) open(ctx context.Context, rp *vfs.ResolvingPath, flags uint32,
 		fd.vfsfd.Init(&fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{})
 		if flags&linux.O_TRUNC != 0 {
 			impl.mu.Lock()
-			impl.data = impl.data[:0]
-			atomic.StoreInt64(&impl.dataLen, 0)
+			impl.data.Truncate(0, impl.memFile)
+			atomic.StoreUint64(&impl.size, 0)
 			impl.mu.Unlock()
 		}
 		return &fd.vfsfd, nil
diff --git a/pkg/sentry/fsimpl/memfs/named_pipe.go b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
index b5a204438..40bde54de 100644
--- a/pkg/sentry/fsimpl/memfs/named_pipe.go
+++ b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package memfs
+package tmpfs
 
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
diff --git a/pkg/sentry/fsimpl/memfs/pipe_test.go b/pkg/sentry/fsimpl/tmpfs/pipe_test.go
index 807c1af7a..70b42a6ec 100644
--- a/pkg/sentry/fsimpl/memfs/pipe_test.go
+++ b/pkg/sentry/fsimpl/tmpfs/pipe_test.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package memfs
+package tmpfs
 
 import (
 	"bytes"
@@ -152,10 +152,10 @@ func setup(t *testing.T) (context.Context, *auth.Credentials, *vfs.VirtualFilesy
 
 	// Create VFS.
 	vfsObj := vfs.New()
-	vfsObj.MustRegisterFilesystemType("memfs", FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
+	vfsObj.MustRegisterFilesystemType("tmpfs", FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
 		AllowUserMount: true,
 	})
-	mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "memfs", &vfs.GetFilesystemOptions{})
+	mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "tmpfs", &vfs.GetFilesystemOptions{})
 	if err != nil {
 		t.Fatalf("failed to create tmpfs root mount: %v", err)
 	}
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
new file mode 100644
index 000000000..f51e247a7
--- /dev/null
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -0,0 +1,357 @@
+// 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 tmpfs
+
+import (
+	"io"
+	"math"
+	"sync"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/usage"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+type regularFile struct {
+	inode inode
+
+	// memFile is a platform.File used to allocate pages to this regularFile.
+	memFile *pgalloc.MemoryFile
+
+	// mu protects the fields below.
+	mu sync.RWMutex
+
+	// data maps offsets into the file to offsets into memFile that store
+	// the file's data.
+	data fsutil.FileRangeSet
+
+	// size is the size of data, but accessed using atomic memory
+	// operations to avoid locking in inode.stat().
+	size uint64
+
+	// seals represents file seals on this inode.
+	seals uint32
+}
+
+func (fs *filesystem) newRegularFile(creds *auth.Credentials, mode linux.FileMode) *inode {
+	file := &regularFile{
+		memFile: fs.memFile,
+	}
+	file.inode.init(file, fs, creds, mode)
+	file.inode.nlink = 1 // from parent directory
+	return &file.inode
+}
+
+type regularFileFD struct {
+	fileDescription
+
+	// These are immutable.
+	readable bool
+	writable bool
+
+	// off is the file offset. off is accessed using atomic memory operations.
+	// offMu serializes operations that may mutate off.
+	off   int64
+	offMu sync.Mutex
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *regularFileFD) Release() {
+	if fd.writable {
+		fd.vfsfd.VirtualDentry().Mount().EndWrite()
+	}
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	if !fd.readable {
+		return 0, syserror.EINVAL
+	}
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+	if dst.NumBytes() == 0 {
+		return 0, nil
+	}
+	f := fd.inode().impl.(*regularFile)
+	rw := getRegularFileReadWriter(f, offset)
+	n, err := dst.CopyOutFrom(ctx, rw)
+	putRegularFileReadWriter(rw)
+	return int64(n), err
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	fd.offMu.Lock()
+	n, err := fd.PRead(ctx, dst, fd.off, opts)
+	fd.off += n
+	fd.offMu.Unlock()
+	return n, err
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	if !fd.writable {
+		return 0, syserror.EINVAL
+	}
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+	srclen := src.NumBytes()
+	if srclen == 0 {
+		return 0, nil
+	}
+	f := fd.inode().impl.(*regularFile)
+	end := offset + srclen
+	if end < offset {
+		// Overflow.
+		return 0, syserror.EFBIG
+	}
+	rw := getRegularFileReadWriter(f, offset)
+	n, err := src.CopyInTo(ctx, rw)
+	putRegularFileReadWriter(rw)
+	return n, err
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *regularFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	fd.offMu.Lock()
+	n, err := fd.PWrite(ctx, src, fd.off, opts)
+	fd.off += n
+	fd.offMu.Unlock()
+	return n, err
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *regularFileFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	fd.offMu.Lock()
+	defer fd.offMu.Unlock()
+	switch whence {
+	case linux.SEEK_SET:
+		// use offset as specified
+	case linux.SEEK_CUR:
+		offset += fd.off
+	case linux.SEEK_END:
+		offset += int64(atomic.LoadUint64(&fd.inode().impl.(*regularFile).size))
+	default:
+		return 0, syserror.EINVAL
+	}
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+	fd.off = offset
+	return offset, nil
+}
+
+// Sync implements vfs.FileDescriptionImpl.Sync.
+func (fd *regularFileFD) Sync(ctx context.Context) error {
+	return nil
+}
+
+// regularFileReadWriter implements safemem.Reader and Safemem.Writer.
+type regularFileReadWriter struct {
+	file *regularFile
+
+	// Offset into the file to read/write at. Note that this may be
+	// different from the FD offset if PRead/PWrite is used.
+	off uint64
+}
+
+var regularFileReadWriterPool = sync.Pool{
+	New: func() interface{} {
+		return &regularFileReadWriter{}
+	},
+}
+
+func getRegularFileReadWriter(file *regularFile, offset int64) *regularFileReadWriter {
+	rw := regularFileReadWriterPool.Get().(*regularFileReadWriter)
+	rw.file = file
+	rw.off = uint64(offset)
+	return rw
+}
+
+func putRegularFileReadWriter(rw *regularFileReadWriter) {
+	rw.file = nil
+	regularFileReadWriterPool.Put(rw)
+}
+
+// ReadToBlocks implements safemem.Reader.ReadToBlocks.
+func (rw *regularFileReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	rw.file.mu.RLock()
+
+	// Compute the range to read (limited by file size and overflow-checked).
+	if rw.off >= rw.file.size {
+		rw.file.mu.RUnlock()
+		return 0, io.EOF
+	}
+	end := rw.file.size
+	if rend := rw.off + dsts.NumBytes(); rend > rw.off && rend < end {
+		end = rend
+	}
+
+	var done uint64
+	seg, gap := rw.file.data.Find(uint64(rw.off))
+	for rw.off < end {
+		mr := memmap.MappableRange{uint64(rw.off), uint64(end)}
+		switch {
+		case seg.Ok():
+			// Get internal mappings.
+			ims, err := rw.file.memFile.MapInternal(seg.FileRangeOf(seg.Range().Intersect(mr)), usermem.Read)
+			if err != nil {
+				rw.file.mu.RUnlock()
+				return done, err
+			}
+
+			// Copy from internal mappings.
+			n, err := safemem.CopySeq(dsts, ims)
+			done += n
+			rw.off += uint64(n)
+			dsts = dsts.DropFirst64(n)
+			if err != nil {
+				rw.file.mu.RUnlock()
+				return done, err
+			}
+
+			// Continue.
+			seg, gap = seg.NextNonEmpty()
+
+		case gap.Ok():
+			// Tmpfs holes are zero-filled.
+			gapmr := gap.Range().Intersect(mr)
+			dst := dsts.TakeFirst64(gapmr.Length())
+			n, err := safemem.ZeroSeq(dst)
+			done += n
+			rw.off += uint64(n)
+			dsts = dsts.DropFirst64(n)
+			if err != nil {
+				rw.file.mu.RUnlock()
+				return done, err
+			}
+
+			// Continue.
+			seg, gap = gap.NextSegment(), fsutil.FileRangeGapIterator{}
+		}
+	}
+	rw.file.mu.RUnlock()
+	return done, nil
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+func (rw *regularFileReadWriter) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	rw.file.mu.Lock()
+
+	// Compute the range to write (overflow-checked).
+	end := rw.off + srcs.NumBytes()
+	if end <= rw.off {
+		end = math.MaxInt64
+	}
+
+	// Check if seals prevent either file growth or all writes.
+	switch {
+	case rw.file.seals&linux.F_SEAL_WRITE != 0: // Write sealed
+		rw.file.mu.Unlock()
+		return 0, syserror.EPERM
+	case end > rw.file.size && rw.file.seals&linux.F_SEAL_GROW != 0: // Grow sealed
+		// When growth is sealed, Linux effectively allows writes which would
+		// normally grow the file to partially succeed up to the current EOF,
+		// rounded down to the page boundary before the EOF.
+		//
+		// This happens because writes (and thus the growth check) for tmpfs
+		// files proceed page-by-page on Linux, and the final write to the page
+		// containing EOF fails, resulting in a partial write up to the start of
+		// that page.
+		//
+		// To emulate this behaviour, artifically truncate the write to the
+		// start of the page containing the current EOF.
+		//
+		// See Linux, mm/filemap.c:generic_perform_write() and
+		// mm/shmem.c:shmem_write_begin().
+		if pgstart := uint64(usermem.Addr(rw.file.size).RoundDown()); end > pgstart {
+			end = pgstart
+		}
+		if end <= rw.off {
+			// Truncation would result in no data being written.
+			rw.file.mu.Unlock()
+			return 0, syserror.EPERM
+		}
+	}
+
+	// Page-aligned mr for when we need to allocate memory. RoundUp can't
+	// overflow since end is an int64.
+	pgstartaddr := usermem.Addr(rw.off).RoundDown()
+	pgendaddr, _ := usermem.Addr(end).RoundUp()
+	pgMR := memmap.MappableRange{uint64(pgstartaddr), uint64(pgendaddr)}
+
+	var (
+		done   uint64
+		retErr error
+	)
+	seg, gap := rw.file.data.Find(uint64(rw.off))
+	for rw.off < end {
+		mr := memmap.MappableRange{uint64(rw.off), uint64(end)}
+		switch {
+		case seg.Ok():
+			// Get internal mappings.
+			ims, err := rw.file.memFile.MapInternal(seg.FileRangeOf(seg.Range().Intersect(mr)), usermem.Write)
+			if err != nil {
+				retErr = err
+				goto exitLoop
+			}
+
+			// Copy to internal mappings.
+			n, err := safemem.CopySeq(ims, srcs)
+			done += n
+			rw.off += uint64(n)
+			srcs = srcs.DropFirst64(n)
+			if err != nil {
+				retErr = err
+				goto exitLoop
+			}
+
+			// Continue.
+			seg, gap = seg.NextNonEmpty()
+
+		case gap.Ok():
+			// Allocate memory for the write.
+			gapMR := gap.Range().Intersect(pgMR)
+			fr, err := rw.file.memFile.Allocate(gapMR.Length(), usage.Tmpfs)
+			if err != nil {
+				retErr = err
+				goto exitLoop
+			}
+
+			// Write to that memory as usual.
+			seg, gap = rw.file.data.Insert(gap, gapMR, fr.Start), fsutil.FileRangeGapIterator{}
+		}
+	}
+exitLoop:
+	// If the write ends beyond the file's previous size, it causes the
+	// file to grow.
+	if rw.off > rw.file.size {
+		atomic.StoreUint64(&rw.file.size, rw.off)
+	}
+
+	rw.file.mu.Unlock()
+	return done, retErr
+}
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file_test.go b/pkg/sentry/fsimpl/tmpfs/regular_file_test.go
new file mode 100644
index 000000000..3731c5b6f
--- /dev/null
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file_test.go
@@ -0,0 +1,224 @@
+// 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 tmpfs
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"testing"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/contexttest"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+)
+
+// newFileFD creates a new file in a new tmpfs mount, and returns the FD. If
+// the returned err is not nil, then cleanup should be called when the FD is no
+// longer needed.
+func newFileFD(ctx context.Context, filename string) (*vfs.FileDescription, func(), error) {
+	creds := auth.CredentialsFromContext(ctx)
+
+	vfsObj := vfs.New()
+	vfsObj.MustRegisterFilesystemType("tmpfs", FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
+		AllowUserMount: true,
+	})
+	mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "tmpfs", &vfs.GetFilesystemOptions{})
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to create tmpfs root mount: %v", err)
+	}
+	root := mntns.Root()
+
+	// Create the file that will be write/read.
+	fd, err := vfsObj.OpenAt(ctx, creds, &vfs.PathOperation{
+		Root:               root,
+		Start:              root,
+		Path:               fspath.Parse(filename),
+		FollowFinalSymlink: true,
+	}, &vfs.OpenOptions{
+		Flags: linux.O_RDWR | linux.O_CREAT | linux.O_EXCL,
+		Mode:  0644,
+	})
+	if err != nil {
+		root.DecRef()
+		mntns.DecRef(vfsObj)
+		return nil, nil, fmt.Errorf("failed to create file %q: %v", filename, err)
+	}
+
+	return fd, func() {
+		root.DecRef()
+		mntns.DecRef(vfsObj)
+	}, nil
+}
+
+// Test that we can write some data to a file and read it back.`
+func TestSimpleWriteRead(t *testing.T) {
+	ctx := contexttest.Context(t)
+	fd, cleanup, err := newFileFD(ctx, "simpleReadWrite")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer cleanup()
+
+	// Write.
+	data := []byte("foobarbaz")
+	n, err := fd.Write(ctx, usermem.BytesIOSequence(data), vfs.WriteOptions{})
+	if err != nil {
+		t.Fatalf("fd.Write failed: %v", err)
+	}
+	if n != int64(len(data)) {
+		t.Errorf("fd.Write got short write length %d, want %d", n, len(data))
+	}
+	if got, want := fd.Impl().(*regularFileFD).off, int64(len(data)); got != want {
+		t.Errorf("fd.Write left offset at %d, want %d", got, want)
+	}
+
+	// Seek back to beginning.
+	if _, err := fd.Seek(ctx, 0, linux.SEEK_SET); err != nil {
+		t.Fatalf("fd.Seek failed: %v", err)
+	}
+	if got, want := fd.Impl().(*regularFileFD).off, int64(0); got != want {
+		t.Errorf("fd.Seek(0) left offset at %d, want %d", got, want)
+	}
+
+	// Read.
+	buf := make([]byte, len(data))
+	n, err = fd.Read(ctx, usermem.BytesIOSequence(buf), vfs.ReadOptions{})
+	if err != nil && err != io.EOF {
+		t.Fatalf("fd.Read failed: %v", err)
+	}
+	if n != int64(len(data)) {
+		t.Errorf("fd.Read got short read length %d, want %d", n, len(data))
+	}
+	if got, want := string(buf), string(data); got != want {
+		t.Errorf("Read got %q want %s", got, want)
+	}
+	if got, want := fd.Impl().(*regularFileFD).off, int64(len(data)); got != want {
+		t.Errorf("fd.Write left offset at %d, want %d", got, want)
+	}
+}
+
+func TestPWrite(t *testing.T) {
+	ctx := contexttest.Context(t)
+	fd, cleanup, err := newFileFD(ctx, "PRead")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer cleanup()
+
+	// Fill file with 1k 'a's.
+	data := bytes.Repeat([]byte{'a'}, 1000)
+	n, err := fd.Write(ctx, usermem.BytesIOSequence(data), vfs.WriteOptions{})
+	if err != nil {
+		t.Fatalf("fd.Write failed: %v", err)
+	}
+	if n != int64(len(data)) {
+		t.Errorf("fd.Write got short write length %d, want %d", n, len(data))
+	}
+
+	// Write "gVisor is awesome" at various offsets.
+	buf := []byte("gVisor is awesome")
+	offsets := []int{0, 1, 2, 10, 20, 50, 100, len(data) - 100, len(data) - 1, len(data), len(data) + 1}
+	for _, offset := range offsets {
+		name := fmt.Sprintf("PWrite offset=%d", offset)
+		t.Run(name, func(t *testing.T) {
+			n, err := fd.PWrite(ctx, usermem.BytesIOSequence(buf), int64(offset), vfs.WriteOptions{})
+			if err != nil {
+				t.Errorf("fd.PWrite got err %v want nil", err)
+			}
+			if n != int64(len(buf)) {
+				t.Errorf("fd.PWrite got %d bytes want %d", n, len(buf))
+			}
+
+			// Update data to reflect expected file contents.
+			if len(data) < offset+len(buf) {
+				data = append(data, make([]byte, (offset+len(buf))-len(data))...)
+			}
+			copy(data[offset:], buf)
+
+			// Read the whole file and compare with data.
+			readBuf := make([]byte, len(data))
+			n, err = fd.PRead(ctx, usermem.BytesIOSequence(readBuf), 0, vfs.ReadOptions{})
+			if err != nil {
+				t.Fatalf("fd.PRead failed: %v", err)
+			}
+			if n != int64(len(data)) {
+				t.Errorf("fd.PRead got short read length %d, want %d", n, len(data))
+			}
+			if got, want := string(readBuf), string(data); got != want {
+				t.Errorf("PRead got %q want %s", got, want)
+			}
+
+		})
+	}
+}
+
+func TestPRead(t *testing.T) {
+	ctx := contexttest.Context(t)
+	fd, cleanup, err := newFileFD(ctx, "PRead")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer cleanup()
+
+	// Write 100 sequences of 'gVisor is awesome'.
+	data := bytes.Repeat([]byte("gVisor is awsome"), 100)
+	n, err := fd.Write(ctx, usermem.BytesIOSequence(data), vfs.WriteOptions{})
+	if err != nil {
+		t.Fatalf("fd.Write failed: %v", err)
+	}
+	if n != int64(len(data)) {
+		t.Errorf("fd.Write got short write length %d, want %d", n, len(data))
+	}
+
+	// Read various sizes from various offsets.
+	sizes := []int{0, 1, 2, 10, 20, 50, 100, 1000}
+	offsets := []int{0, 1, 2, 10, 20, 50, 100, 1000, len(data) - 100, len(data) - 1, len(data), len(data) + 1}
+
+	for _, size := range sizes {
+		for _, offset := range offsets {
+			name := fmt.Sprintf("PRead offset=%d size=%d", offset, size)
+			t.Run(name, func(t *testing.T) {
+				var (
+					wantRead []byte
+					wantErr  error
+				)
+				if offset < len(data) {
+					wantRead = data[offset:]
+				} else if size > 0 {
+					wantErr = io.EOF
+				}
+				if offset+size < len(data) {
+					wantRead = wantRead[:size]
+				}
+				buf := make([]byte, size)
+				n, err := fd.PRead(ctx, usermem.BytesIOSequence(buf), int64(offset), vfs.ReadOptions{})
+				if err != wantErr {
+					t.Errorf("fd.PRead got err %v want %v", err, wantErr)
+				}
+				if n != int64(len(wantRead)) {
+					t.Errorf("fd.PRead got %d bytes want %d", n, len(wantRead))
+				}
+				if got := string(buf[:n]); got != string(wantRead) {
+					t.Errorf("fd.PRead got %q want %q", got, string(wantRead))
+				}
+			})
+		}
+	}
+}
diff --git a/pkg/sentry/fsimpl/memfs/symlink.go b/pkg/sentry/fsimpl/tmpfs/symlink.go
index b2ac2cbeb..5246aca84 100644
--- a/pkg/sentry/fsimpl/memfs/symlink.go
+++ b/pkg/sentry/fsimpl/tmpfs/symlink.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package memfs
+package tmpfs
 
 import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
diff --git a/pkg/sentry/fsimpl/memfs/memfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index 8d0167c93..7be6faa5b 100644
--- a/pkg/sentry/fsimpl/memfs/memfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -12,20 +12,16 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package memfs provides a filesystem implementation that behaves like tmpfs:
+// Package tmpfs provides a filesystem implementation that behaves like tmpfs:
 // the Dentry tree is the sole source of truth for the state of the filesystem.
 //
-// memfs is intended primarily to demonstrate filesystem implementation
-// patterns. Real uses cases for an in-memory filesystem should use tmpfs
-// instead.
-//
 // Lock order:
 //
 // filesystem.mu
 //   regularFileFD.offMu
 //     regularFile.mu
 //   inode.mu
-package memfs
+package tmpfs
 
 import (
 	"fmt"
@@ -36,6 +32,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/context"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -47,6 +44,9 @@ type FilesystemType struct{}
 type filesystem struct {
 	vfsfs vfs.Filesystem
 
+	// memFile is used to allocate pages to for regular files.
+	memFile *pgalloc.MemoryFile
+
 	// mu serializes changes to the Dentry tree.
 	mu sync.RWMutex
 
@@ -55,7 +55,13 @@ type filesystem struct {
 
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
 func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
-	var fs filesystem
+	memFileProvider := pgalloc.MemoryFileProviderFromContext(ctx)
+	if memFileProvider == nil {
+		panic("MemoryFileProviderFromContext returned nil")
+	}
+	fs := filesystem{
+		memFile: memFileProvider.MemoryFile(),
+	}
 	fs.vfsfs.Init(vfsObj, &fs)
 	root := fs.newDentry(fs.newDirectory(creds, 01777))
 	return &fs.vfsfs, &root.vfsd, nil
@@ -74,11 +80,11 @@ type dentry struct {
 	// immutable.
 	inode *inode
 
-	// memfs doesn't count references on dentries; because the dentry tree is
+	// tmpfs doesn't count references on dentries; because the dentry tree is
 	// the sole source of truth, it is by definition always consistent with the
 	// state of the filesystem. However, it does count references on inodes,
 	// because inode resources are released when all references are dropped.
-	// (memfs doesn't really have resources to release, but we implement
+	// (tmpfs doesn't really have resources to release, but we implement
 	// reference counting because tmpfs regular files will.)
 
 	// dentryEntry (ugh) links dentries into their parent directory.childList.
@@ -150,7 +156,7 @@ func (i *inode) init(impl interface{}, fs *filesystem, creds *auth.Credentials,
 // i.nlink < maxLinks.
 func (i *inode) incLinksLocked() {
 	if i.nlink == 0 {
-		panic("memfs.inode.incLinksLocked() called with no existing links")
+		panic("tmpfs.inode.incLinksLocked() called with no existing links")
 	}
 	if i.nlink == maxLinks {
 		panic("memfs.inode.incLinksLocked() called with maximum link count")
@@ -163,14 +169,14 @@ func (i *inode) incLinksLocked() {
 // Preconditions: filesystem.mu must be locked for writing. i.nlink != 0.
 func (i *inode) decLinksLocked() {
 	if i.nlink == 0 {
-		panic("memfs.inode.decLinksLocked() called with no existing links")
+		panic("tmpfs.inode.decLinksLocked() called with no existing links")
 	}
 	atomic.AddUint32(&i.nlink, ^uint32(0))
 }
 
 func (i *inode) incRef() {
 	if atomic.AddInt64(&i.refs, 1) <= 1 {
-		panic("memfs.inode.incRef() called without holding a reference")
+		panic("tmpfs.inode.incRef() called without holding a reference")
 	}
 }
 
@@ -189,14 +195,14 @@ func (i *inode) tryIncRef() bool {
 func (i *inode) decRef() {
 	if refs := atomic.AddInt64(&i.refs, -1); refs == 0 {
 		// This is unnecessary; it's mostly to simulate what tmpfs would do.
-		if regfile, ok := i.impl.(*regularFile); ok {
-			regfile.mu.Lock()
-			regfile.data = nil
-			atomic.StoreInt64(&regfile.dataLen, 0)
-			regfile.mu.Unlock()
+		if regFile, ok := i.impl.(*regularFile); ok {
+			regFile.mu.Lock()
+			regFile.data.DropAll(regFile.memFile)
+			atomic.StoreUint64(&regFile.size, 0)
+			regFile.mu.Unlock()
 		}
 	} else if refs < 0 {
-		panic("memfs.inode.decRef() called without holding a reference")
+		panic("tmpfs.inode.decRef() called without holding a reference")
 	}
 }
 
@@ -220,7 +226,7 @@ func (i *inode) statTo(stat *linux.Statx) {
 	case *regularFile:
 		stat.Mode |= linux.S_IFREG
 		stat.Mask |= linux.STATX_SIZE | linux.STATX_BLOCKS
-		stat.Size = uint64(atomic.LoadInt64(&impl.dataLen))
+		stat.Size = uint64(atomic.LoadUint64(&impl.size))
 		// In tmpfs, this will be FileRangeSet.Span() / 512 (but also cached in
 		// a uint64 accessed using atomic memory operations to avoid taking
 		// locks).
@@ -261,7 +267,7 @@ func (i *inode) direntType() uint8 {
 	}
 }
 
-// fileDescription is embedded by memfs implementations of
+// fileDescription is embedded by tmpfs implementations of
 // vfs.FileDescriptionImpl.
 type fileDescription struct {
 	vfsfd vfs.FileDescription