Move vfs.RestoreID to checkpoint.ResourceID.

... and use it everywhere in preference to its string. This is to be able to
reliably inspect pgalloc.MemoryFile.ResourceID().Path in cl/879147587.

PiperOrigin-RevId: 883274090

pkg/sentry/checkpoint/BUILD

@@ -0,0 +1,11 @@
+load("//tools:defs.bzl", "go_library")
+
+package(default_applicable_licenses = ["//:license"])
+
+licenses(["notice"])
+
+go_library(
+    name = "checkpoint",
+    srcs = ["checkpoint.go"],
+    visibility = ["//pkg/sentry:internal"],
+)

pkg/sentry/checkpoint/checkpoint.go

@@ -0,0 +1,42 @@
+// Copyright 2026 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 checkpoint defines types that are used by multiple forms of gVisor
+// checkpoints.
+package checkpoint
+
+import (
+	"fmt"
+)
+
+// ResourceID is a unique ID that is used to identify resources between save/restore sessions.
+// Examples of resources are host files, gofer connection for mount points, etc.
+//
+// +stateify savable
+type ResourceID struct {
+	// ContainerName is the name of the container that the resource belongs to.
+	ContainerName string `json:"container_name"`
+	// Path is the path of the resource. Path is never empty for a valid
+	// ResourceID.
+	Path string `json:"path"`
+}
+
+// Ok returns true if the ResourceID is valid and not the zero value.
+func (id ResourceID) Ok() bool {
+	return id.Path != ""
+}
+
+func (id ResourceID) String() string {
+	return fmt.Sprintf("%s:%s", id.ContainerName, id.Path)
+}

pkg/sentry/fdimport/fdimport.go

@@ -77,7 +77,7 @@ func Import(ctx context.Context, fdTable *kernel.FDTable, fds map[int]*fd.FD, op
 		}
 		var appFile *vfs.FileDescription
 
-		fdOpts.RestoreKey = host.MakeRestoreID(opts.ContainerName, appFD)
+		fdOpts.RestoreKey = host.MakeResourceID(opts.ContainerName, appFD)
 		if opts.Console && appFD < 3 {
 			// Import the file as a host TTY file.
 			if ttyFile == nil {

pkg/sentry/fsimpl/erofs/BUILD

@@ -65,6 +65,7 @@ go_library(
         "//pkg/log",
         "//pkg/refs",
         "//pkg/safemem",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/fsimpl/lock",
         "//pkg/sentry/fsutil",
         "//pkg/sentry/kernel/auth",

pkg/sentry/fsimpl/erofs/erofs.go

@@ -26,6 +26,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/erofs"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
@@ -82,9 +83,9 @@ type filesystem struct {
 //
 // +stateify savable
 type InternalFilesystemOptions struct {
-	// If UniqueID is non-empty, it is an opaque string used to reassociate the
-	// filesystem with a new image FD during restoration from checkpoint.
-	UniqueID vfs.RestoreID
+	// If UniqueID is non-empty, it is used to reassociate the filesystem with
+	// a new image FD during restoration from checkpoint.
+	UniqueID checkpoint.ResourceID
 }
 
 // Name implements vfs.FilesystemType.Name.

pkg/sentry/fsimpl/gofer/BUILD

@@ -108,6 +108,7 @@ go_library(
         "//pkg/rand",
         "//pkg/refs",
         "//pkg/safemem",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/fsimpl/host",
         "//pkg/sentry/fsimpl/lock",
         "//pkg/sentry/fsmetric",

pkg/sentry/fsimpl/gofer/gofer.go

@@ -58,6 +58,7 @@ import (
 	"gvisor.dev/gvisor/pkg/lisafs"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	fslock "gvisor.dev/gvisor/pkg/sentry/fsimpl/lock"
 	"gvisor.dev/gvisor/pkg/sentry/fsutil"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -410,9 +411,9 @@ const (
 //
 // +stateify savable
 type InternalFilesystemOptions struct {
-	// If UniqueID is non-empty, it is an opaque string used to reassociate the
-	// filesystem with a new server FD during restoration from checkpoint.
-	UniqueID vfs.RestoreID
+	// If UniqueID is non-empty, it is used to reassociate the filesystem with
+	// a new server FD during restoration from checkpoint.
+	UniqueID checkpoint.ResourceID
 
 	// If LeakConnection is true, do not close the connection to the server
 	// when the Filesystem is released. This is necessary for deployments in

pkg/sentry/fsimpl/host/BUILD

@@ -42,6 +42,7 @@ go_library(
         "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/fsimpl/eventfd",
         "//pkg/sentry/fsimpl/kernfs",
         "//pkg/sentry/fsimpl/lock",

pkg/sentry/fsimpl/host/host.go

@@ -30,6 +30,7 @@ import (
 	"gvisor.dev/gvisor/pkg/hostarch"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/eventfd"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
 	"gvisor.dev/gvisor/pkg/sentry/fsutil"
@@ -117,7 +118,7 @@ type inode struct {
 	hostFD int `state:"nosave"`
 
 	// restoreKey is used to identify the `hostFD` after a restore is performed.
-	restoreKey vfs.RestoreID
+	restoreKey checkpoint.ResourceID
 
 	// ino is an inode number unique within this filesystem.
 	//
@@ -194,7 +195,7 @@ type inode struct {
 	termios   linux.KernelTermios
 }
 
-func newInode(ctx context.Context, fs *filesystem, hostFD int, savable bool, restoreKey vfs.RestoreID, fileType linux.FileMode, isTTY bool, readonly bool) (*inode, error) {
+func newInode(ctx context.Context, fs *filesystem, hostFD int, savable bool, restoreKey checkpoint.ResourceID, fileType linux.FileMode, isTTY bool, readonly bool) (*inode, error) {
 	// Determine if hostFD is seekable.
 	_, err := unix.Seek(hostFD, 0, linux.SEEK_CUR)
 	seekable := !linuxerr.Equals(linuxerr.ESPIPE, err)
@@ -249,7 +250,7 @@ type NewFDOptions struct {
 	// RestoreKey is only used when Savable==true. It uniquely identifies the
 	// host FD so that a mapping to the corresponding FD can be provided during
 	// restore.
-	RestoreKey vfs.RestoreID
+	RestoreKey checkpoint.ResourceID
 
 	// Restorable is true if hostFD may be restored. This can be set to false
 	// for host FDs that are not going to be present after restore.

pkg/sentry/fsimpl/host/save_restore.go

@@ -24,16 +24,18 @@ import (
 	"gvisor.dev/gvisor/pkg/hostarch"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/hostfd"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
 
-// MakeRestoreID creates a RestoreID for a given application FD. The application
-// FD remains the same between restores, e.g. stdout=2 before and after restore,
-// but the host FD that is maps to can change between restores. This ID is used
-// to map application FDs to their respective FD after a restore happens.
-func MakeRestoreID(containerName string, fd int) vfs.RestoreID {
-	return vfs.RestoreID{
+// MakeResourceID creates a ResourceID for a given application FD. The
+// application FD remains the same between restores, e.g. stdout=2 before and
+// after restore, but the host FD that is maps to can change between restores.
+// This ID is used to map application FDs to their respective FD after a
+// restore happens.
+func MakeResourceID(containerName string, fd int) checkpoint.ResourceID {
+	return checkpoint.ResourceID{
 		ContainerName: containerName,
 		Path:          fmt.Sprintf("host:%d", fd),
 	}

pkg/sentry/fsimpl/tmpfs/BUILD

@@ -98,6 +98,9 @@ go_library(
         "tar.go",
         "tmpfs.go",
     ],
+    imports = [
+        "gvisor.dev/gvisor/pkg/sentry/checkpoint",
+    ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
@@ -112,6 +115,7 @@ go_library(
         "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/fsimpl/lock",
         "//pkg/sentry/fsmetric",
         "//pkg/sentry/fsutil",

pkg/sentry/fsimpl/tmpfs/save_restore.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
@@ -26,16 +27,16 @@ import (
 var _ vfs.FilesystemImplSaveRestoreExtension = (*filesystem)(nil)
 
 // saveMf is called by stateify.
-func (fs *filesystem) saveMf() string {
+func (fs *filesystem) saveMf() checkpoint.ResourceID {
 	if !fs.mf.IsSavable() {
 		panic(fmt.Sprintf("Can't save tmpfs filesystem because its MemoryFile is not savable: %v", fs.mf))
 	}
-	return fs.mf.RestoreID()
+	return fs.mf.ResourceID()
 }
 
 // loadMf is called by stateify.
-func (fs *filesystem) loadMf(ctx goContext.Context, restoreID string) {
-	if restoreID == "" {
+func (fs *filesystem) loadMf(ctx goContext.Context, resourceID checkpoint.ResourceID) {
+	if !resourceID.Ok() {
 		fs.mf = pgalloc.MemoryFileFromContext(ctx)
 		return
 	}
@@ -43,9 +44,9 @@ func (fs *filesystem) loadMf(ctx goContext.Context, restoreID string) {
 	if mfmap == nil {
 		panic("CtxMemoryFileMap was not provided")
 	}
-	mf, ok := mfmap[restoreID]
+	mf, ok := mfmap[resourceID]
 	if !ok {
-		panic(fmt.Sprintf("Memory file for %q not found in CtxMemoryFileMap", restoreID))
+		panic(fmt.Sprintf("Memory file for %q not found in CtxMemoryFileMap", resourceID))
 	}
 	fs.mf = mf
 }
@@ -62,18 +63,18 @@ func (d *dentry) loadParent(_ goContext.Context, parent *dentry) {
 
 // PrepareSave implements vfs.FilesystemImplSaveRestoreExtension.PrepareSave.
 func (fs *filesystem) PrepareSave(ctx context.Context) error {
-	restoreID := fs.mf.RestoreID()
-	if restoreID == "" {
+	resourceID := fs.mf.ResourceID()
+	if !resourceID.Ok() {
 		return nil
 	}
 	mfmap := pgalloc.MemoryFileMapFromContext(ctx)
 	if mfmap == nil {
 		return fmt.Errorf("CtxMemoryFileMap was not provided")
 	}
-	if _, ok := mfmap[restoreID]; ok {
-		return fmt.Errorf("memory file for %q already exists in CtxMemoryFileMap", restoreID)
+	if _, ok := mfmap[resourceID]; ok {
+		return fmt.Errorf("memory file for %q already exists in CtxMemoryFileMap", resourceID)
 	}
-	mfmap[restoreID] = fs.mf
+	mfmap[resourceID] = fs.mf
 	return nil
 }
 

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -67,7 +67,7 @@ type filesystem struct {
 
 	// mf is used to allocate memory that stores regular file contents. mf is
 	// immutable, except it is changed during restore.
-	mf *pgalloc.MemoryFile `state:".(string)"`
+	mf *pgalloc.MemoryFile `state:".(checkpoint.ResourceID)"`
 
 	// clock is a realtime clock used to set timestamps in file operations.
 	clock ktime.Clock
@@ -350,9 +350,9 @@ func (fs *filesystem) Release(ctx context.Context) {
 		fs.ovlWhiteout.inode.decLinksLocked(ctx)
 	}
 	fs.mu.Unlock()
-	if fs.mf.RestoreID() != "" {
-		// If RestoreID is set, then this is a private MemoryFile which needs to be
-		// destroyed since this tmpfs is the only user.
+	if fs.mf.ResourceID().Ok() {
+		// If ResourceID is set, then this is a private MemoryFile which needs
+		// to be destroyed since this tmpfs is the only user.
 		fs.mf.Destroy()
 	}
 }

pkg/sentry/kernel/BUILD

@@ -360,6 +360,7 @@ go_library(
         "//pkg/safemem",
         "//pkg/secio",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/devices/nvproxy/nvconf",
         "//pkg/sentry/fdcollector",
         "//pkg/sentry/fsimpl/kernfs",

pkg/sentry/kernel/kernel.go

@@ -55,6 +55,7 @@ import (
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/devices/nvproxy/nvconf"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/nsfs"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/pipefs"
@@ -597,10 +598,10 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 
 // +stateify savable
 type privateMemoryFileMetadata struct {
-	owners []string
+	owners []checkpoint.ResourceID
 }
 
-func savePrivateMFs(ctx context.Context, w io.Writer, mfsToSave map[string]*pgalloc.MemoryFile, mfOpts *pgalloc.SaveOpts) error {
+func savePrivateMFs(ctx context.Context, w io.Writer, mfsToSave map[checkpoint.ResourceID]*pgalloc.MemoryFile, mfOpts *pgalloc.SaveOpts) error {
 	var meta privateMemoryFileMetadata
 	// Generate the order in which private memory files are saved.
 	for fsID := range mfsToSave {
@@ -664,7 +665,7 @@ func (k *Kernel) SaveTo(ctx context.Context, stateFile, pagesMetadata io.WriteCl
 	}
 
 	// Capture all private memory files.
-	mfsToSave := make(map[string]*pgalloc.MemoryFile)
+	mfsToSave := make(map[checkpoint.ResourceID]*pgalloc.MemoryFile)
 	vfsCtx := context.WithValue(ctx, pgalloc.CtxMemoryFileMap, mfsToSave)
 	// Prepare filesystems for saving. This must be done after
 	// invalidateUnsavableMappings(), since dropping memory mappings may
@@ -769,7 +770,7 @@ func (k *Kernel) BeforeResume(ctx context.Context) {
 // pagesFile must be non-nil, saveMemoryFiles takes ownership of both
 // pagesMetadata and pagesFile (even if it returns a non-nil error), and
 // MemoryFile state will be saved to pagesMetadata and pagesFile.
-func (k *Kernel) saveMemoryFiles(ctx context.Context, w io.Writer, pagesMetadata io.WriteCloser, pagesFile stateio.AsyncWriter, mfsToSave map[string]*pgalloc.MemoryFile, appMFExcludeCommittedZeroPages bool) error {
+func (k *Kernel) saveMemoryFiles(ctx context.Context, w io.Writer, pagesMetadata io.WriteCloser, pagesFile stateio.AsyncWriter, mfsToSave map[checkpoint.ResourceID]*pgalloc.MemoryFile, appMFExcludeCommittedZeroPages bool) error {
 	memoryStart := time.Now()
 
 	pmw := w

pkg/sentry/kernel/kernel_restore.go

@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/cleanup"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
 	"gvisor.dev/gvisor/pkg/sentry/state/stateio"
 	"gvisor.dev/gvisor/pkg/state"
@@ -210,7 +211,7 @@ func (w *CheckpointWaitable) signal(gen CheckpointGeneration, err error) {
 // loadPrivateMemoryFiles loads the private MemoryFiles from mfmap and it reads
 // private MemoryFile metadata from `r`. This consumes bytes from `r`, so this
 // must be called only once.
-func loadPrivateMemoryFiles(ctx context.Context, r io.Reader, mfmap map[string]*pgalloc.MemoryFile, opts *pgalloc.LoadOpts) error {
+func loadPrivateMemoryFiles(ctx context.Context, r io.Reader, mfmap map[checkpoint.ResourceID]*pgalloc.MemoryFile, opts *pgalloc.LoadOpts) error {
 	// Load the metadata.
 	var meta privateMemoryFileMetadata
 	if _, err := state.Load(ctx, r, &meta); err != nil {
@@ -258,7 +259,7 @@ func (k *Kernel) loadMemoryFiles(ctx context.Context, r io.Reader) error {
 type AsyncMFLoader struct {
 	// privateMFsChan is used to tell the background goroutine about private
 	// MemoryFiles, once they are known. This channel is written to exactly once.
-	privateMFsChan chan map[string]*pgalloc.MemoryFile
+	privateMFsChan chan map[checkpoint.ResourceID]*pgalloc.MemoryFile
 
 	mainMFStartWg   sync.WaitGroup
 	mainMetadataErr error
@@ -279,7 +280,7 @@ type AsyncMFLoader struct {
 // pages.
 func NewAsyncMFLoader(pagesMetadata io.ReadCloser, pagesFile stateio.AsyncReader, mainMF *pgalloc.MemoryFile, timeline *timing.Timeline) *AsyncMFLoader {
 	mfl := &AsyncMFLoader{
-		privateMFsChan: make(chan map[string]*pgalloc.MemoryFile, 1),
+		privateMFsChan: make(chan map[checkpoint.ResourceID]*pgalloc.MemoryFile, 1),
 	}
 	mfl.mainMFStartWg.Add(1)
 	mfl.metadataWg.Add(1)
@@ -351,7 +352,7 @@ func (mfl *AsyncMFLoader) backgroundGoroutine(pagesMetadata io.ReadCloser, pages
 }
 
 // KickoffPrivate notifies the background goroutine of the private MemoryFiles.
-func (mfl *AsyncMFLoader) KickoffPrivate(mfmap map[string]*pgalloc.MemoryFile) {
+func (mfl *AsyncMFLoader) KickoffPrivate(mfmap map[checkpoint.ResourceID]*pgalloc.MemoryFile) {
 	mfl.privateMFsChan <- mfmap
 }
 

pkg/sentry/mm/BUILD

@@ -147,6 +147,9 @@ go_library(
         "vma.go",
         "vma_set.go",
     ],
+    imports = [
+        "gvisor.dev/gvisor/pkg/sentry/checkpoint",
+    ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
@@ -159,6 +162,7 @@ go_library(
         "//pkg/safecopy",
         "//pkg/safemem",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/futex",
         "//pkg/sentry/kernel/shm",

pkg/sentry/mm/mm.go

@@ -330,7 +330,7 @@ type pma struct {
 	// file is the file mapped by this pma. Only pmas for which file is of type
 	// pgalloc.MemoryFile may be saved. pmas hold a reference to the
 	// corresponding file range while they exist.
-	file memmap.File `state:".(string)"`
+	file memmap.File `state:".(checkpoint.ResourceID)"`
 
 	// off is the offset into file at which this pma begins.
 	off uint64

pkg/sentry/mm/save_restore.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
 )
 
@@ -150,7 +151,7 @@ func (v *vma) loadRealPerms(_ goContext.Context, b int) {
 	}
 }
 
-func (p *pma) saveFile() string {
+func (p *pma) saveFile() checkpoint.ResourceID {
 	mf, ok := p.file.(*pgalloc.MemoryFile)
 	if !ok {
 		// InvalidateUnsavable should have caused all such pmas to be
@@ -160,18 +161,18 @@ func (p *pma) saveFile() string {
 	if !mf.IsSavable() {
 		panic(fmt.Sprintf("Can't save pma because its MemoryFile is not savable: %v", mf))
 	}
-	return mf.RestoreID()
+	return mf.ResourceID()
 }
 
-func (p *pma) loadFile(ctx goContext.Context, restoreID string) {
-	if restoreID == "" {
+func (p *pma) loadFile(ctx goContext.Context, resourceID checkpoint.ResourceID) {
+	if !resourceID.Ok() {
 		p.file = pgalloc.MemoryFileFromContext(ctx)
 		return
 	}
 	mfmap := pgalloc.MemoryFileMapFromContext(ctx)
-	mf, ok := mfmap[restoreID]
+	mf, ok := mfmap[resourceID]
 	if !ok {
-		panic(fmt.Sprintf("can't restore pma because its MemoryFile's restore ID %q was not found in CtxMemoryFileMap", restoreID))
+		panic(fmt.Sprintf("can't restore pma because its MemoryFile's resource ID %q was not found in CtxMemoryFileMap", resourceID))
 	}
 	p.file = mf
 }

pkg/sentry/pgalloc/BUILD

@@ -185,6 +185,7 @@ go_library(
         "//pkg/ringdeque",
         "//pkg/safemem",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/hostmm",
         "//pkg/sentry/memmap",
         "//pkg/sentry/state/stateio",

pkg/sentry/pgalloc/context.go

@@ -16,6 +16,8 @@ package pgalloc
 
 import (
 	"context"
+
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 )
 
 // contextID is this package's type for context.Context.Value keys.
@@ -53,9 +55,9 @@ func MemoryCgroupIDFromContext(ctx context.Context) uint32 {
 
 // MemoryFileMapFromContext returns the memory file map used by ctx, or nil if
 // no such map exists.
-func MemoryFileMapFromContext(ctx context.Context) map[string]*MemoryFile {
+func MemoryFileMapFromContext(ctx context.Context) map[checkpoint.ResourceID]*MemoryFile {
 	if v := ctx.Value(CtxMemoryFileMap); v != nil {
-		return v.(map[string]*MemoryFile)
+		return v.(map[checkpoint.ResourceID]*MemoryFile)
 	}
 	return nil
 }

pkg/sentry/pgalloc/pgalloc.go

@@ -38,6 +38,7 @@ import (
 	"gvisor.dev/gvisor/pkg/hostarch"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/hostmm"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
@@ -361,9 +362,9 @@ type MemoryFileOpts struct {
 	// DiskBackedFile indicates that the MemoryFile is backed by a file on disk.
 	DiskBackedFile bool
 
-	// RestoreID is an opaque string used to reassociate the MemoryFile with its
-	// replacement during restore.
-	RestoreID string
+	// ResourceID is used to reassociate the MemoryFile with its replacement
+	// during restore.
+	ResourceID checkpoint.ResourceID
 
 	// If ExpectHugepages is true, MemoryFile will expect that the host will
 	// attempt to back AllocOpts.Huge == true allocations with huge pages. If

pkg/sentry/pgalloc/save_restore.go

@@ -33,6 +33,7 @@ import (
 	"gvisor.dev/gvisor/pkg/hostarch"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/ringdeque"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/state/stateio"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
@@ -57,9 +58,9 @@ func (f *MemoryFile) IsSavable() bool {
 	return f.savable
 }
 
-// RestoreID returns the restore ID for f.
-func (f *MemoryFile) RestoreID() string {
-	return f.opts.RestoreID
+// ResourceID returns the resource ID for f.
+func (f *MemoryFile) ResourceID() checkpoint.ResourceID {
+	return f.opts.ResourceID
 }
 
 // memoryFileSaved is the subset of MemoryFile that is stored in checkpoints.

pkg/sentry/vfs/BUILD

@@ -189,6 +189,7 @@ go_library(
         "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/arch",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/fsimpl/lock",
         "//pkg/sentry/fsmetric",
         "//pkg/sentry/kernel/auth",

pkg/sentry/vfs/context.go

@@ -18,6 +18,7 @@ import (
 	goContext "context"
 
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 )
 
 // contextID is this package's type for context.Context.Value keys.
@@ -30,9 +31,9 @@ const (
 	// CtxRoot is a Context.Value key for a VFS root.
 	CtxRoot
 
-	// CtxRestoreFilesystemFDMap is a Context.Value key for a map[string]int
-	// mapping filesystem unique IDs (cf. gofer.InternalFilesystemOptions.UniqueID)
-	// to host FDs.
+	// CtxRestoreFilesystemFDMap is a Context.Value key for a
+	// map[checkpoint.ResourceID]int mapping filesystem unique IDs (cf.
+	// gofer.InternalFilesystemOptions.UniqueID) to host FDs.
 	CtxRestoreFilesystemFDMap
 )
 
@@ -49,8 +50,8 @@ func MountNamespaceFromContext(ctx goContext.Context) *MountNamespace {
 
 // RestoreFilesystemFDMapFromContext returns the RestoreFilesystemFDMap used
 // by ctx. If ctx is not associated with a RestoreFilesystemFDMap, returns nil.
-func RestoreFilesystemFDMapFromContext(ctx goContext.Context) map[RestoreID]int {
-	fdmap, ok := ctx.Value(CtxRestoreFilesystemFDMap).(map[RestoreID]int)
+func RestoreFilesystemFDMapFromContext(ctx goContext.Context) map[checkpoint.ResourceID]int {
+	fdmap, ok := ctx.Value(CtxRestoreFilesystemFDMap).(map[checkpoint.ResourceID]int)
 	if !ok {
 		return nil
 	}

pkg/sentry/vfs/save_restore.go

@@ -179,18 +179,3 @@ func (epi *epollInterest) afterLoad(goContext.Context) {
 	// EpollInstance.ReadEvents() rechecks their readiness.
 	epi.waiter.NotifyEvent(waiter.EventMaskFromLinux(epi.mask))
 }
-
-// RestoreID is a unique ID that is used to identify resources between save/restore sessions.
-// Example of resources are host files, gofer connection for mount points, etc.
-//
-// +stateify savable
-type RestoreID struct {
-	// ContainerName is the name of the container that the resource belongs to.
-	ContainerName string
-	// Path is the path of the resource.
-	Path string
-}
-
-func (f RestoreID) String() string {
-	return fmt.Sprintf("%s:%s", f.ContainerName, f.Path)
-}

runsc/boot/BUILD

@@ -57,6 +57,7 @@ go_library(
         "//pkg/refs",
         "//pkg/sentry/arch",
         "//pkg/sentry/arch:registers_go_proto",
+        "//pkg/sentry/checkpoint",
         "//pkg/sentry/control",
         "//pkg/sentry/devices/memdev",
         "//pkg/sentry/devices/nvproxy",

runsc/boot/restore.go

@@ -28,6 +28,7 @@ import (
 	"gvisor.dev/gvisor/pkg/devutil"
 	"gvisor.dev/gvisor/pkg/fd"
 	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/control"
 	"gvisor.dev/gvisor/pkg/sentry/devices/nvproxy/nvconf"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
@@ -241,8 +242,8 @@ func (r *restorer) restore(l *Loader) error {
 	})
 	defer cu.Clean()
 
-	fdmap := make(map[vfs.RestoreID]int)
-	mfmap := make(map[string]*pgalloc.MemoryFile)
+	fdmap := make(map[checkpoint.ResourceID]int)
+	mfmap := make(map[checkpoint.ResourceID]*pgalloc.MemoryFile)
 	for _, cont := range r.containers {
 		// TODO(b/298078576): Need to process hints here probably
 		mntr := newContainerMounter(cont, l.k, l.mountHints, l.sharedMounts, l.productName, cont.cid)
@@ -251,11 +252,11 @@ func (r *restorer) restore(l *Loader) error {
 		}
 
 		for i, fd := range cont.stdioFDs {
-			key := host.MakeRestoreID(cont.containerName, i)
+			key := host.MakeResourceID(cont.containerName, i)
 			fdmap[key] = fd.Release()
 		}
 		for _, customFD := range cont.passFDs {
-			key := host.MakeRestoreID(cont.containerName, customFD.guest)
+			key := host.MakeResourceID(cont.containerName, customFD.guest)
 			fdmap[key] = customFD.host.FD()
 		}
 	}

runsc/boot/vfs.go

@@ -36,6 +36,7 @@ import (
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/fsutil"
 	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/checkpoint"
 	"gvisor.dev/gvisor/pkg/sentry/devices/memdev"
 	"gvisor.dev/gvisor/pkg/sentry/devices/nvproxy"
 	"gvisor.dev/gvisor/pkg/sentry/devices/nvproxy/nvconf"
@@ -511,7 +512,7 @@ func (c *containerMounter) createMountNamespace(ctx context.Context, conf *confi
 				InternalMount: true,
 				Data:          strings.Join(data, ","),
 				InternalData: gofer.InternalFilesystemOptions{
-					UniqueID: vfs.RestoreID{
+					UniqueID: checkpoint.ResourceID{
 						ContainerName: c.containerName,
 						Path:          "/",
 					},
@@ -527,7 +528,7 @@ func (c *containerMounter) createMountNamespace(ctx context.Context, conf *confi
 				InternalMount: true,
 				Data:          fmt.Sprintf("ifd=%d", ioFD),
 				InternalData: erofs.InternalFilesystemOptions{
-					UniqueID: vfs.RestoreID{
+					UniqueID: checkpoint.ResourceID{
 						ContainerName: c.containerName,
 						Path:          "/",
 					},
@@ -647,7 +648,7 @@ func (c *containerMounter) configureOverlay(ctx context.Context, conf *config.Co
 	}
 	if filestoreFD != nil {
 		// Create memory file for disk-backed overlays.
-		mf, err := createPrivateMemoryFile(filestoreFD.ReleaseToFile("overlay-filestore"), vfs.RestoreID{ContainerName: c.containerName, Path: dst})
+		mf, err := createPrivateMemoryFile(filestoreFD.ReleaseToFile("overlay-filestore"), checkpoint.ResourceID{ContainerName: c.containerName, Path: dst})
 		if err != nil {
 			return nil, nil, fmt.Errorf("failed to create memory file for overlay: %v", err)
 		}
@@ -950,7 +951,7 @@ func getMountNameAndOptions(spec *specs.Spec, conf *config.Config, m *mountInfo,
 			return "", nil, err
 		}
 		if m.filestoreFD != nil {
-			mf, err := createPrivateMemoryFile(m.filestoreFD.ReleaseToFile("tmpfs-filestore"), vfs.RestoreID{ContainerName: containerName, Path: m.mount.Destination})
+			mf, err := createPrivateMemoryFile(m.filestoreFD.ReleaseToFile("tmpfs-filestore"), checkpoint.ResourceID{ContainerName: containerName, Path: m.mount.Destination})
 			if err != nil {
 				return "", nil, fmt.Errorf("failed to create memory file for tmpfs: %v", err)
 			}
@@ -975,7 +976,7 @@ func getMountNameAndOptions(spec *specs.Spec, conf *config.Config, m *mountInfo,
 		}
 		data = append(data, goferMountData(m.goferFD.Release(), getMountAccessType(conf, m.hint), conf)...)
 		internalData = gofer.InternalFilesystemOptions{
-			UniqueID: vfs.RestoreID{
+			UniqueID: checkpoint.ResourceID{
 				ContainerName: containerName,
 				Path:          m.mount.Destination,
 			},
@@ -994,7 +995,7 @@ func getMountNameAndOptions(spec *specs.Spec, conf *config.Config, m *mountInfo,
 		}
 		data = []string{fmt.Sprintf("ifd=%d", m.goferFD.Release())}
 		internalData = erofs.InternalFilesystemOptions{
-			UniqueID: vfs.RestoreID{
+			UniqueID: checkpoint.ResourceID{
 				ContainerName: containerName,
 				Path:          m.mount.Destination,
 			},
@@ -1052,7 +1053,7 @@ func parseKeyValue(s string) (string, string, bool) {
 	return strings.TrimSpace(tokens[0]), strings.TrimSpace(tokens[1]), true
 }
 
-func createPrivateMemoryFile(file *os.File, restoreID vfs.RestoreID) (*pgalloc.MemoryFile, error) {
+func createPrivateMemoryFile(file *os.File, resourceID checkpoint.ResourceID) (*pgalloc.MemoryFile, error) {
 	mfOpts := pgalloc.MemoryFileOpts{
 		// Private memory files are usually backed by files on disk. Ideally we
 		// would confirm with fstatfs(2) but that is prohibited by seccomp.
@@ -1064,7 +1065,7 @@ func createPrivateMemoryFile(file *os.File, restoreID vfs.RestoreID) (*pgalloc.M
 		// are expected to have performed the work around outside the sandbox.
 		DisableIMAWorkAround: true,
 		// Private memory files need to be restored correctly using this ID.
-		RestoreID: restoreID.String(),
+		ResourceID: resourceID,
 	}
 	return pgalloc.NewMemoryFile(file, mfOpts)
 }
@@ -1392,10 +1393,10 @@ func (c *containerMounter) makeMountPoint(
 
 // configureRestore returns an updated context.Context including filesystem
 // state used by restore defined by conf.
-func (c *containerMounter) configureRestore(fdmap map[vfs.RestoreID]int, mfmap map[string]*pgalloc.MemoryFile) error {
+func (c *containerMounter) configureRestore(fdmap map[checkpoint.ResourceID]int, mfmap map[checkpoint.ResourceID]*pgalloc.MemoryFile) error {
 	// Compare createMountNamespace(); rootfs always consumes a gofer FD and a
 	// filestore FD is consumed if the rootfs GoferMountConf indicates so.
-	rootKey := vfs.RestoreID{ContainerName: c.containerName, Path: "/"}
+	rootKey := checkpoint.ResourceID{ContainerName: c.containerName, Path: "/"}
 	fdmap[rootKey] = c.goferFDs.remove()
 
 	if rootfsConf := c.goferMountConfs[0]; rootfsConf.IsFilestorePresent() {
@@ -1403,7 +1404,7 @@ func (c *containerMounter) configureRestore(fdmap map[vfs.RestoreID]int, mfmap m
 		if err != nil {
 			return fmt.Errorf("failed to create private memory file for mount rootfs: %w", err)
 		}
-		mfmap[rootKey.String()] = mf
+		mfmap[rootKey] = mf
 	}
 	// prepareMounts() consumes the remaining FDs for submounts.
 	mounts, err := c.prepareMounts()
@@ -1413,16 +1414,16 @@ func (c *containerMounter) configureRestore(fdmap map[vfs.RestoreID]int, mfmap m
 	for i := range mounts {
 		submount := &mounts[i]
 		if submount.goferFD != nil {
-			key := vfs.RestoreID{ContainerName: c.containerName, Path: submount.mount.Destination}
+			key := checkpoint.ResourceID{ContainerName: c.containerName, Path: submount.mount.Destination}
 			fdmap[key] = submount.goferFD.Release()
 		}
 		if submount.filestoreFD != nil {
-			key := vfs.RestoreID{ContainerName: c.containerName, Path: submount.mount.Destination}
+			key := checkpoint.ResourceID{ContainerName: c.containerName, Path: submount.mount.Destination}
 			mf, err := createPrivateMemoryFile(submount.filestoreFD.ReleaseToFile("overlay-filestore"), key)
 			if err != nil {
 				return fmt.Errorf("failed to create private memory file for mount %q: %w", submount.mount.Destination, err)
 			}
-			mfmap[key.String()] = mf
+			mfmap[key] = mf
 		}
 	}
 	return nil