namespace: extract show_path() helper

To be used by the statmount(2) syscall as well.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20231025140205.3586473-4-mszeredi@redhat.comReviewed-by: Ian Kent <raven@themaw.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/internal.h

@@ -83,6 +83,8 @@ int path_mount(const char *dev_name, struct path *path,
 		const char *type_page, unsigned long flags, void *data_page);
 int path_umount(struct path *path, int flags);
 
+int show_path(struct seq_file *m, struct dentry *root);
+
 /*
  * fs_struct.c
  */

fs/namespace.c

@@ -4674,6 +4674,15 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
 	return err;
 }
 
+int show_path(struct seq_file *m, struct dentry *root)
+{
+	if (root->d_sb->s_op->show_path)
+		return root->d_sb->s_op->show_path(m, root);
+
+	seq_dentry(m, root, " \t\n\\");
+	return 0;
+}
+
 static void __init init_mount_tree(void)
 {
 	struct vfsmount *mnt;

fs/proc_namespace.c

@@ -142,13 +142,9 @@ static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt)
 
 	seq_printf(m, "%i %i %u:%u ", r->mnt_id, r->mnt_parent->mnt_id,
 		   MAJOR(sb->s_dev), MINOR(sb->s_dev));
-	if (sb->s_op->show_path) {
-		err = sb->s_op->show_path(m, mnt->mnt_root);
-		if (err)
-			goto out;
-	} else {
-		seq_dentry(m, mnt->mnt_root, " \t\n\\");
-	}
+	err = show_path(m, mnt->mnt_root);
+	if (err)
+		goto out;
 	seq_putc(m, ' ');
 
 	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */