Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 95 insertions, 0 deletions

diff --git a/pkg/sentry/fs/mount_overlay.go b/pkg/sentry/fs/mount_overlay.go
new file mode 100644
index 000000000..16c25e46c
--- /dev/null
+++ b/pkg/sentry/fs/mount_overlay.go
@@ -0,0 +1,95 @@
+// 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 fs
+
+import "gvisor.googlesource.com/gvisor/pkg/sentry/context"
+
+// overlayMountSourceOperations implements MountSourceOperations for an overlay
+// mount point.
+type overlayMountSourceOperations struct {
+	upper *MountSource
+	lower *MountSource
+}
+
+func newOverlayMountSource(upper, lower *MountSource, flags MountSourceFlags) *MountSource {
+	upper.IncRef()
+	lower.IncRef()
+	return NewMountSource(&overlayMountSourceOperations{
+		upper: upper,
+		lower: lower,
+	}, &overlayFilesystem{}, flags)
+}
+
+// Revalidate panics if the upper or lower MountSource require that dirent be
+// revalidated. Otherwise always returns false.
+func (o *overlayMountSourceOperations) Revalidate(dirent *Dirent) bool {
+	if o.upper.Revalidate(dirent) || o.lower.Revalidate(dirent) {
+		panic("an overlay cannot revalidate file objects")
+	}
+	return false
+}
+
+// Keep returns true if either upper or lower MountSource require that the
+// dirent be kept in memory.
+func (o *overlayMountSourceOperations) Keep(dirent *Dirent) bool {
+	return o.upper.Keep(dirent) || o.lower.Keep(dirent)
+}
+
+// ResetInodeMappings propagates the call to both upper and lower MountSource.
+func (o *overlayMountSourceOperations) ResetInodeMappings() {
+	o.upper.ResetInodeMappings()
+	o.lower.ResetInodeMappings()
+}
+
+// SaveInodeMapping propagates the call to both upper and lower MountSource.
+func (o *overlayMountSourceOperations) SaveInodeMapping(inode *Inode, path string) {
+	inode.overlay.copyMu.RLock()
+	defer inode.overlay.copyMu.RUnlock()
+	if inode.overlay.upper != nil {
+		o.upper.SaveInodeMapping(inode.overlay.upper, path)
+	}
+	if inode.overlay.lower != nil {
+		o.lower.SaveInodeMapping(inode.overlay.lower, path)
+	}
+}
+
+// Destroy drops references on the upper and lower MountSource.
+func (o *overlayMountSourceOperations) Destroy() {
+	o.upper.DecRef()
+	o.lower.DecRef()
+}
+
+// type overlayFilesystem is the filesystem for overlay mounts.
+type overlayFilesystem struct{}
+
+// Name implements Filesystem.Name.
+func (ofs *overlayFilesystem) Name() string {
+	return "overlayfs"
+}
+
+// Flags implements Filesystem.Flags.
+func (ofs *overlayFilesystem) Flags() FilesystemFlags {
+	return 0
+}
+
+// AllowUserMount implements Filesystem.AllowUserMount.
+func (ofs *overlayFilesystem) AllowUserMount() bool {
+	return false
+}
+
+// Mount implements Filesystem.Mount.
+func (ofs *overlayFilesystem) Mount(ctx context.Context, device string, flags MountSourceFlags, data string) (*Inode, error) {
+	panic("overlayFilesystem.Mount should not be called!")
+}