vfs: introduce CtxRestoreFilesystemFDMap

This patch introduces CtxRestoreFilesystemFDMap in vfs to replace
the CtxRestoreServerFDMap defined in gofer, which is a preparation
for adding the checkpoint/restore support in EROFS. It allows the
configureRestore() in boot/vfs.go to be agnostic to the filesystems
that will be used in the sentry when configuring restore.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>

pkg/sentry/fsimpl/gofer/save_restore.go

@@ -29,15 +29,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
 
-type saveRestoreContextID int
-
-const (
-	// CtxRestoreServerFDMap is a Context.Value key for a map[string]int
-	// mapping filesystem unique IDs (cf. InternalFilesystemOptions.UniqueID)
-	// to host FDs.
-	CtxRestoreServerFDMap saveRestoreContextID = iota
-)
-
 // +stateify savable
 type savedDentryRW struct {
 	read  bool
@@ -181,7 +172,7 @@ func (d *dentry) loadParent(parent *dentry) {
 // CompleteRestore implements
 // vfs.FilesystemImplSaveRestoreExtension.CompleteRestore.
 func (fs *filesystem) CompleteRestore(ctx context.Context, opts vfs.CompleteRestoreOptions) error {
-	fdmapv := ctx.Value(CtxRestoreServerFDMap)
+	fdmapv := ctx.Value(vfs.CtxRestoreFilesystemFDMap)
 	if fdmapv == nil {
 		return fmt.Errorf("no server FD map available")
 	}

pkg/sentry/vfs/context.go

@@ -27,6 +27,11 @@ 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
 )
 
 // MountNamespaceFromContext returns the MountNamespace used by ctx. If ctx is

runsc/boot/vfs.go

@@ -1087,7 +1087,7 @@ func (c *containerMounter) configureRestore(ctx context.Context) (context.Contex
 			fdmap[submount.mount.Destination] = submount.goferFD.Release()
 		}
 	}
-	return context.WithValue(ctx, gofer.CtxRestoreServerFDMap, fdmap), nil
+	return context.WithValue(ctx, vfs.CtxRestoreFilesystemFDMap, fdmap), nil
 }
 
 func createDeviceFiles(ctx context.Context, creds *auth.Credentials, info *containerInfo, vfsObj *vfs.VirtualFilesystem, root vfs.VirtualDentry) error {