1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (c) 2026 Christian Brauner <brauner@kernel.org> */ 3 #include <linux/fs/super_types.h> 4 #include <linux/fs_context.h> 5 #include <linux/magic.h> 6 7 #include "mount.h" 8 9 static const struct super_operations nullfs_super_operations = { 10 .statfs = simple_statfs, 11 }; 12 13 static int nullfs_fs_fill_super(struct super_block *s, struct fs_context *fc) 14 { 15 struct inode *inode; 16 17 s->s_maxbytes = MAX_LFS_FILESIZE; 18 s->s_blocksize = PAGE_SIZE; 19 s->s_blocksize_bits = PAGE_SHIFT; 20 s->s_magic = NULL_FS_MAGIC; 21 s->s_op = &nullfs_super_operations; 22 s->s_export_op = NULL; 23 s->s_xattr = NULL; 24 s->s_time_gran = 1; 25 s->s_d_flags = 0; 26 27 inode = new_inode(s); 28 if (!inode) 29 return -ENOMEM; 30 31 /* nullfs is permanently empty... */ 32 make_empty_dir_inode(inode); 33 simple_inode_init_ts(inode); 34 inode->i_ino = 1; 35 /* ... and immutable. */ 36 inode->i_flags |= S_IMMUTABLE; 37 38 s->s_root = d_make_root(inode); 39 if (!s->s_root) 40 return -ENOMEM; 41 42 return 0; 43 } 44 45 static int nullfs_fs_get_tree(struct fs_context *fc) 46 { 47 return get_tree_nodev(fc, nullfs_fs_fill_super); 48 } 49 50 static const struct fs_context_operations nullfs_fs_context_ops = { 51 .get_tree = nullfs_fs_get_tree, 52 }; 53 54 static int nullfs_init_fs_context(struct fs_context *fc) 55 { 56 fc->ops = &nullfs_fs_context_ops; 57 fc->sb_flags |= SB_NOUSER; 58 fc->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; 59 return 0; 60 } 61 62 struct file_system_type nullfs_fs_type = { 63 .name = "nullfs", 64 .init_fs_context = nullfs_init_fs_context, 65 .kill_sb = kill_anon_super, 66 }; 67