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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187// 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>#include <linux/splice.h>#include <linux/uio.h>
#include "mount.h"
static const struct super_operations nullfs_super_operations = { .statfs = simple_statfs,};
static loff_t nullfs_dir_llseek(struct file *file, loff_t offset, int whence){ /* an empty directory has two entries . and .. at offsets 0 and 1 */ return generic_file_llseek_size(file, offset, whence, 2, 2);}
static int nullfs_dir_readdir(struct file *file, struct dir_context *ctx){ dir_emit_dots(file, ctx); return 0;}
/* the one inode of nullfs is shared by every holder, so no locks on it */static int nullfs_nolock(struct file *file, int cmd, struct file_lock *fl){ return -ENOLCK;}
/* what libfs gives an empty directory, plus the refusal of file locks */static const struct file_operations nullfs_dir_operations = { .llseek = nullfs_dir_llseek, .read = generic_read_dir, .iterate_shared = nullfs_dir_readdir, .fsync = noop_fsync, .lock = nullfs_nolock, .flock = nullfs_nolock, .fop_flags = FOP_IMMUTABLE,};
static ssize_t nullfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to){ return 0;}
static ssize_t nullfs_file_splice_read(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags){ return 0;}
static ssize_t nullfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from){ size_t count = iov_iter_count(from);
iov_iter_advance(from, count); return count;}
static int nullfs_pipe_to_null(struct pipe_inode_info *pipe, struct pipe_buffer *buf, struct splice_desc *sd){ return sd->len;}
static ssize_t nullfs_file_splice_write(struct pipe_inode_info *pipe, struct file *out, loff_t *ppos, size_t len, unsigned int flags){ return splice_from_pipe(pipe, out, ppos, len, flags, nullfs_pipe_to_null);}
static int nullfs_file_setattr(const struct mnt_idmap *idmap, struct dentry *dentry, struct iattr *attr){ if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) return -EPERM; return 0;}
static const struct inode_operations nullfs_file_inode_operations = { .setattr = nullfs_file_setattr,};
static const struct file_operations nullfs_file_operations = { .llseek = generic_file_llseek, .read_iter = nullfs_file_read_iter, .write_iter = nullfs_file_write_iter, .splice_read = nullfs_file_splice_read, .splice_write = nullfs_file_splice_write, .fsync = noop_fsync, .lock = nullfs_nolock, .flock = nullfs_nolock,};
/* * An empty regular file on @sb as a dentry of its own, never hashed under * the root so no lookup finds it. */struct dentry *nullfs_new_file(struct super_block *sb){ struct dentry *dentry; struct inode *inode;
inode = new_inode(sb); if (!inode) return ERR_PTR(-ENOMEM);
/* the root directory is 1 */ inode->i_ino = 2; inode->i_mode = S_IFREG | 0666; inode->i_op = &nullfs_file_inode_operations; inode->i_fop = &nullfs_file_operations; simple_inode_init_ts(inode); inode->i_flags |= S_NOATIME;
dentry = d_alloc_anon(sb); if (!dentry) { iput(inode); return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); return dentry;}
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); inode->i_fop = &nullfs_dir_operations; simple_inode_init_ts(inode); inode->i_ino = 1; /* ... and immutable, reading it leaves no trace either. */ inode->i_flags |= S_IMMUTABLE | S_NOATIME;
s->s_root = d_make_root(inode); if (!s->s_root) return -ENOMEM;
return 0;}
static int nullfs_fs_get_tree(struct fs_context *fc){ return get_tree_nodev(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->sb_flags |= SB_NOUSER; fc->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; return 0;}
struct file_system_type nullfs_fs_type = { .name = "nullfs", .fs_flags = FS_DISALLOW_NOTIFY, .init_fs_context = nullfs_init_fs_context, .kill_sb = kill_anon_super,};