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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071// 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,};