// SPDX-License-Identifier: GPL-2.0-only/* Copyright (c) 2026 Christian Brauner <brauner@kernel.org> */#include <linux/fs/super_types.h>#include <linux/fs_context.h>#include <linux/magic.h> static const struct super_operations nullfs_super_operations = {	.statfs	= simple_statfs,}; static int nullfs_fs_fill_super(struct super_block *s, struct fs_context *fc){	struct inode *inode; 	s->s_maxbytes		= MAX_LFS_FILESIZE;	s->s_blocksize		= PAGE_SIZE;	s->s_blocksize_bits	= PAGE_SHIFT;	s->s_magic		= NULL_FS_MAGIC;	s->s_op			= &nullfs_super_operations;	s->s_export_op		= NULL;	s->s_xattr		= NULL;	s->s_time_gran		= 1;	s->s_d_flags		= 0; 	inode = new_inode(s);	if (!inode)		return -ENOMEM; 	/* nullfs is permanently empty... */	make_empty_dir_inode(inode);	simple_inode_init_ts(inode);	inode->i_ino	= 1;	/* ... and immutable. */	inode->i_flags |= S_IMMUTABLE; 	s->s_root = d_make_root(inode);	if (!s->s_root)		return -ENOMEM; 	return 0;} /* * For now this is a single global instance. If needed we can make it * mountable by userspace at which point we will need to make it * multi-instance. */static int nullfs_fs_get_tree(struct fs_context *fc){	return get_tree_single(fc, nullfs_fs_fill_super);} static const struct fs_context_operations nullfs_fs_context_ops = {	.get_tree	= nullfs_fs_get_tree,}; static int nullfs_init_fs_context(struct fs_context *fc){	fc->ops		= &nullfs_fs_context_ops;	fc->global	= true;	fc->sb_flags	= SB_NOUSER;	fc->s_iflags	= SB_I_NOEXEC | SB_I_NODEV;	return 0;} struct file_system_type nullfs_fs_type = {	.name			= "nullfs",	.init_fs_context	= nullfs_init_fs_context,	.kill_sb		= kill_anon_super,};