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

1 files changed, 10 insertions, 1 deletions

diff --git a/pkg/sentry/vfs/genericfstree/genericfstree.go b/pkg/sentry/vfs/genericfstree/genericfstree.go
index 2d27d9d35..ba6e6ed49 100644
--- a/pkg/sentry/vfs/genericfstree/genericfstree.go
+++ b/pkg/sentry/vfs/genericfstree/genericfstree.go
@@ -71,7 +71,7 @@ func PrependPath(vfsroot vfs.VirtualDentry, mnt *vfs.Mount, d *Dentry, b *fspath
 		if mnt == vfsroot.Mount() && &d.vfsd == vfsroot.Dentry() {
 			return vfs.PrependPathAtVFSRootError{}
 		}
-		if &d.vfsd == mnt.Root() {
+		if mnt != nil && &d.vfsd == mnt.Root() {
 			return nil
 		}
 		if d.parent == nil {
@@ -81,3 +81,12 @@ func PrependPath(vfsroot vfs.VirtualDentry, mnt *vfs.Mount, d *Dentry, b *fspath
 		d = d.parent
 	}
 }
+
+// DebugPathname returns a pathname to d relative to its filesystem root.
+// DebugPathname does not correspond to any Linux function; it's used to
+// generate dentry pathnames for debugging.
+func DebugPathname(d *Dentry) string {
+	var b fspath.Builder
+	_ = PrependPath(vfs.VirtualDentry{}, nil, d, &b)
+	return b.String()
+}