Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 96 insertions, 0 deletions

diff --git a/pkg/sentry/fs/dev/null.go b/pkg/sentry/fs/dev/null.go
new file mode 100644
index 000000000..66b8ba967
--- /dev/null
+++ b/pkg/sentry/fs/dev/null.go
@@ -0,0 +1,96 @@
+// Copyright 2018 Google Inc.
+//
+// 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 dev
+
+import (
+	"io"
+	"math"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/mm"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+)
+
+type nullDevice struct {
+	ramfs.Entry
+}
+
+func newNullDevice(ctx context.Context, owner fs.FileOwner, mode linux.FileMode) *nullDevice {
+	n := &nullDevice{}
+	n.InitEntry(ctx, owner, fs.FilePermsFromMode(mode))
+	return n
+}
+
+// DeprecatedPreadv reads data from the device.
+func (n *nullDevice) DeprecatedPreadv(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+	return 0, io.EOF
+}
+
+// DeprecatedPwritev discards writes.
+func (n *nullDevice) DeprecatedPwritev(_ context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	return src.NumBytes(), nil
+}
+
+// Truncate should be simply ignored for character devices on linux.
+func (n *nullDevice) Truncate(context.Context, *fs.Inode, int64) error {
+	return nil
+}
+
+type zeroDevice struct {
+	nullDevice
+}
+
+func newZeroDevice(ctx context.Context, owner fs.FileOwner, mode linux.FileMode) *zeroDevice {
+	zd := &zeroDevice{}
+	zd.InitEntry(ctx, owner, fs.FilePermsFromMode(mode))
+	return zd
+}
+
+// DeprecatedPreadv implements fs.InodeOperations.DeprecatedPreadv.
+func (zd *zeroDevice) DeprecatedPreadv(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+	return dst.ZeroOut(ctx, math.MaxInt64)
+}
+
+// GetFile overrides ramfs.Entry.GetFile and returns a zeroFile instead.
+func (zd *zeroDevice) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
+	// Allow pread(2) and pwrite(2) on this file.
+	flags.Pread = true
+	flags.Pwrite = true
+
+	return fs.NewFile(ctx, dirent, flags, &zeroFileOperations{
+		FileOperations: &fsutil.Handle{HandleOperations: dirent.Inode.HandleOps()},
+	}), nil
+}
+
+type zeroFileOperations struct {
+	fs.FileOperations
+}
+
+// ConfigureMMap implements fs.FileOperations.ConfigureMMap.
+func (*zeroFileOperations) ConfigureMMap(ctx context.Context, file *fs.File, opts *memmap.MMapOpts) error {
+	m, err := mm.NewSharedAnonMappable(opts.Length, platform.FromContext(ctx))
+	if err != nil {
+		return err
+	}
+	opts.MappingIdentity = m
+	opts.Mappable = m
+	return nil
+}