1 files changed, 89 insertions, 0 deletions
diff --git a/pkg/sentry/devices/memdev/zero.go b/pkg/sentry/devices/memdev/zero.go
new file mode 100644
index 000000000..2e631a252
--- /dev/null
+++ b/pkg/sentry/devices/memdev/zero.go
@@ -0,0 +1,89 @@
+// 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 memdev
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/mm"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+const zeroDevMinor = 5
+
+// zeroDevice implements vfs.Device for /dev/zero.
+type zeroDevice struct{}
+
+// Open implements vfs.Device.Open.
+func (zeroDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &zeroFD{}
+	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
+		UseDentryMetadata: true,
+	}); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+// zeroFD implements vfs.FileDescriptionImpl for /dev/zero.
+type zeroFD struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+	vfs.NoLockFD
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *zeroFD) Release(context.Context) {
+	// noop
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *zeroFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return dst.ZeroOut(ctx, dst.NumBytes())
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *zeroFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	return dst.ZeroOut(ctx, dst.NumBytes())
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *zeroFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return src.NumBytes(), nil
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *zeroFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	return src.NumBytes(), nil
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *zeroFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	return 0, nil
+}
+
+// ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
+func (fd *zeroFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	m, err := mm.NewSharedAnonMappable(opts.Length, pgalloc.MemoryFileProviderFromContext(ctx))
+	if err != nil {
+		return err
+	}
+	opts.MappingIdentity = m
+	opts.Mappable = m
+	return nil
+}