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// 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,
};
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