Support VFS2 save/restore.

Inode number consistency checks are now skipped in save/restore tests for
reasons described in greatest detail in StatTest.StateDoesntChangeAfterRename.
They pass in VFS1 due to the bug described in new test case
SimpleStatTest.DifferentFilesHaveDifferentDeviceInodeNumberPairs.

Fixes #1663

PiperOrigin-RevId: 338776148

4 files changed, 29 insertions, 7 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/BUILD b/pkg/sentry/fsimpl/tmpfs/BUILD
index 85850cf34..fe520b6fd 100644
--- a/pkg/sentry/fsimpl/tmpfs/BUILD
+++ b/pkg/sentry/fsimpl/tmpfs/BUILD
@@ -48,6 +48,7 @@ go_library(
         "inode_refs.go",
         "named_pipe.go",
         "regular_file.go",
+        "save_restore.go",
         "socket_file.go",
         "symlink.go",
         "tmpfs.go",
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index ce4e3eda7..98680fde9 100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -42,7 +42,7 @@ type regularFile struct {
 	inode inode
 
 	// memFile is a platform.File used to allocate pages to this regularFile.
-	memFile *pgalloc.MemoryFile
+	memFile *pgalloc.MemoryFile `state:"nosave"`
 
 	// memoryUsageKind is the memory accounting category under which pages backing
 	// this regularFile's contents are accounted.
@@ -92,7 +92,7 @@ type regularFile struct {
 
 func (fs *filesystem) newRegularFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) *inode {
 	file := &regularFile{
-		memFile:         fs.memFile,
+		memFile:         fs.mfp.MemoryFile(),
 		memoryUsageKind: usage.Tmpfs,
 		seals:           linux.F_SEAL_SEAL,
 	}
diff --git a/pkg/sentry/fsimpl/tmpfs/save_restore.go b/pkg/sentry/fsimpl/tmpfs/save_restore.go
new file mode 100644
index 000000000..b27f75cc2
--- /dev/null
+++ b/pkg/sentry/fsimpl/tmpfs/save_restore.go
@@ -0,0 +1,20 @@
+// 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 tmpfs
+
+// afterLoad is called by stateify.
+func (rf *regularFile) afterLoad() {
+	rf.memFile = rf.inode.fs.mfp.MemoryFile()
+}
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index e2a0aac69..4ce859d57 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -61,8 +61,9 @@ type FilesystemType struct{}
 type filesystem struct {
 	vfsfs vfs.Filesystem
 
-	// memFile is used to allocate pages to for regular files.
-	memFile *pgalloc.MemoryFile
+	// mfp is used to allocate memory that stores regular file contents. mfp is
+	// immutable.
+	mfp pgalloc.MemoryFileProvider
 
 	// clock is a realtime clock used to set timestamps in file operations.
 	clock time.Clock
@@ -106,8 +107,8 @@ type FilesystemOpts struct {
 
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
 func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, _ string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
-	memFileProvider := pgalloc.MemoryFileProviderFromContext(ctx)
-	if memFileProvider == nil {
+	mfp := pgalloc.MemoryFileProviderFromContext(ctx)
+	if mfp == nil {
 		panic("MemoryFileProviderFromContext returned nil")
 	}
 
@@ -181,7 +182,7 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 	}
 	clock := time.RealtimeClockFromContext(ctx)
 	fs := filesystem{
-		memFile:  memFileProvider.MemoryFile(),
+		mfp:      mfp,
 		clock:    clock,
 		devMinor: devMinor,
 	}