1 // SPDX-License-Identifier: GPL-2.0-only
3 * inode.c - part of tracefs, a pseudo file system for activating tracing
5 * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
7 * Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
9 * tracefs is the file system that is used by the tracing infrastructure.
12 #include <linux/module.h>
14 #include <linux/mount.h>
15 #include <linux/kobject.h>
16 #include <linux/namei.h>
17 #include <linux/tracefs.h>
18 #include <linux/fsnotify.h>
19 #include <linux/security.h>
20 #include <linux/seq_file.h>
21 #include <linux/parser.h>
22 #include <linux/magic.h>
23 #include <linux/slab.h>
25 #define TRACEFS_DEFAULT_MODE 0700
27 static struct vfsmount *tracefs_mount;
28 static int tracefs_mount_count;
29 static bool tracefs_registered;
31 static ssize_t default_read_file(struct file *file, char __user *buf,
32 size_t count, loff_t *ppos)
37 static ssize_t default_write_file(struct file *file, const char __user *buf,
38 size_t count, loff_t *ppos)
43 static const struct file_operations tracefs_file_operations = {
44 .read = default_read_file,
45 .write = default_write_file,
47 .llseek = noop_llseek,
50 static struct tracefs_dir_ops {
51 int (*mkdir)(const char *name);
52 int (*rmdir)(const char *name);
53 } tracefs_ops __ro_after_init;
55 static char *get_dname(struct dentry *dentry)
59 int len = dentry->d_name.len;
61 dname = dentry->d_name.name;
62 name = kmalloc(len + 1, GFP_KERNEL);
65 memcpy(name, dname, len);
70 static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
75 name = get_dname(dentry);
80 * The mkdir call can call the generic functions that create
81 * the files within the tracefs system. It is up to the individual
82 * mkdir routine to handle races.
85 ret = tracefs_ops.mkdir(name);
93 static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
98 name = get_dname(dentry);
103 * The rmdir call can call the generic functions that create
104 * the files within the tracefs system. It is up to the individual
105 * rmdir routine to handle races.
106 * This time we need to unlock not only the parent (inode) but
107 * also the directory that is being deleted.
110 inode_unlock(dentry->d_inode);
112 ret = tracefs_ops.rmdir(name);
114 inode_lock_nested(inode, I_MUTEX_PARENT);
115 inode_lock(dentry->d_inode);
122 static const struct inode_operations tracefs_dir_inode_operations = {
123 .lookup = simple_lookup,
124 .mkdir = tracefs_syscall_mkdir,
125 .rmdir = tracefs_syscall_rmdir,
128 static struct inode *tracefs_get_inode(struct super_block *sb)
130 struct inode *inode = new_inode(sb);
132 inode->i_ino = get_next_ino();
133 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
138 struct tracefs_mount_opts {
142 /* Opt_* bitfield. */
153 static const match_table_t tokens = {
156 {Opt_mode, "mode=%o"},
160 struct tracefs_fs_info {
161 struct tracefs_mount_opts mount_opts;
164 static void change_gid(struct dentry *dentry, kgid_t gid)
166 if (!dentry->d_inode)
168 dentry->d_inode->i_gid = gid;
172 * Taken from d_walk, but without he need for handling renames.
173 * Nothing can be renamed while walking the list, as tracefs
174 * does not support renames. This is only called when mounting
175 * or remounting the file system, to set all the files to
178 static void set_gid(struct dentry *parent, kgid_t gid)
180 struct dentry *this_parent;
181 struct list_head *next;
183 this_parent = parent;
184 spin_lock(&this_parent->d_lock);
186 change_gid(this_parent, gid);
188 next = this_parent->d_subdirs.next;
190 while (next != &this_parent->d_subdirs) {
191 struct list_head *tmp = next;
192 struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
195 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
197 change_gid(dentry, gid);
199 if (!list_empty(&dentry->d_subdirs)) {
200 spin_unlock(&this_parent->d_lock);
201 spin_release(&dentry->d_lock.dep_map, _RET_IP_);
202 this_parent = dentry;
203 spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
206 spin_unlock(&dentry->d_lock);
209 * All done at this level ... ascend and resume the search.
213 if (this_parent != parent) {
214 struct dentry *child = this_parent;
215 this_parent = child->d_parent;
217 spin_unlock(&child->d_lock);
218 spin_lock(&this_parent->d_lock);
220 /* go into the first sibling still alive */
222 next = child->d_child.next;
223 if (next == &this_parent->d_subdirs)
225 child = list_entry(next, struct dentry, d_child);
226 } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
231 spin_unlock(&this_parent->d_lock);
235 static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
237 substring_t args[MAX_OPT_ARGS];
245 opts->mode = TRACEFS_DEFAULT_MODE;
247 while ((p = strsep(&data, ",")) != NULL) {
251 token = match_token(p, tokens, args);
254 if (match_int(&args[0], &option))
256 uid = make_kuid(current_user_ns(), option);
262 if (match_int(&args[0], &option))
264 gid = make_kgid(current_user_ns(), option);
270 if (match_octal(&args[0], &option))
272 opts->mode = option & S_IALLUGO;
275 * We might like to report bad mount options here;
276 * but traditionally tracefs has ignored all mount options
280 opts->opts |= BIT(token);
286 static int tracefs_apply_options(struct super_block *sb, bool remount)
288 struct tracefs_fs_info *fsi = sb->s_fs_info;
289 struct inode *inode = sb->s_root->d_inode;
290 struct tracefs_mount_opts *opts = &fsi->mount_opts;
293 * On remount, only reset mode/uid/gid if they were provided as mount
297 if (!remount || opts->opts & BIT(Opt_mode)) {
298 inode->i_mode &= ~S_IALLUGO;
299 inode->i_mode |= opts->mode;
302 if (!remount || opts->opts & BIT(Opt_uid))
303 inode->i_uid = opts->uid;
305 if (!remount || opts->opts & BIT(Opt_gid)) {
306 /* Set all the group ids to the mount option */
307 set_gid(sb->s_root, opts->gid);
313 static int tracefs_remount(struct super_block *sb, int *flags, char *data)
316 struct tracefs_fs_info *fsi = sb->s_fs_info;
319 err = tracefs_parse_options(data, &fsi->mount_opts);
323 tracefs_apply_options(sb, true);
329 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
331 struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
332 struct tracefs_mount_opts *opts = &fsi->mount_opts;
334 if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
335 seq_printf(m, ",uid=%u",
336 from_kuid_munged(&init_user_ns, opts->uid));
337 if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
338 seq_printf(m, ",gid=%u",
339 from_kgid_munged(&init_user_ns, opts->gid));
340 if (opts->mode != TRACEFS_DEFAULT_MODE)
341 seq_printf(m, ",mode=%o", opts->mode);
346 static const struct super_operations tracefs_super_operations = {
347 .statfs = simple_statfs,
348 .remount_fs = tracefs_remount,
349 .show_options = tracefs_show_options,
352 static int trace_fill_super(struct super_block *sb, void *data, int silent)
354 static const struct tree_descr trace_files[] = {{""}};
355 struct tracefs_fs_info *fsi;
358 fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
365 err = tracefs_parse_options(data, &fsi->mount_opts);
369 err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
373 sb->s_op = &tracefs_super_operations;
375 tracefs_apply_options(sb, false);
381 sb->s_fs_info = NULL;
385 static struct dentry *trace_mount(struct file_system_type *fs_type,
386 int flags, const char *dev_name,
389 return mount_single(fs_type, flags, data, trace_fill_super);
392 static struct file_system_type trace_fs_type = {
393 .owner = THIS_MODULE,
395 .mount = trace_mount,
396 .kill_sb = kill_litter_super,
398 MODULE_ALIAS_FS("tracefs");
400 static struct dentry *start_creating(const char *name, struct dentry *parent)
402 struct dentry *dentry;
405 pr_debug("tracefs: creating file '%s'\n",name);
407 error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
408 &tracefs_mount_count);
410 return ERR_PTR(error);
412 /* If the parent is not specified, we create it in the root.
413 * We need the root dentry to do this, which is in the super
414 * block. A pointer to that is in the struct vfsmount that we
418 parent = tracefs_mount->mnt_root;
420 inode_lock(parent->d_inode);
421 if (unlikely(IS_DEADDIR(parent->d_inode)))
422 dentry = ERR_PTR(-ENOENT);
424 dentry = lookup_one_len(name, parent, strlen(name));
425 if (!IS_ERR(dentry) && dentry->d_inode) {
427 dentry = ERR_PTR(-EEXIST);
430 if (IS_ERR(dentry)) {
431 inode_unlock(parent->d_inode);
432 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
438 static struct dentry *failed_creating(struct dentry *dentry)
440 inode_unlock(dentry->d_parent->d_inode);
442 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
446 static struct dentry *end_creating(struct dentry *dentry)
448 inode_unlock(dentry->d_parent->d_inode);
453 * tracefs_create_file - create a file in the tracefs filesystem
454 * @name: a pointer to a string containing the name of the file to create.
455 * @mode: the permission that the file should have.
456 * @parent: a pointer to the parent dentry for this file. This should be a
457 * directory dentry if set. If this parameter is NULL, then the
458 * file will be created in the root of the tracefs filesystem.
459 * @data: a pointer to something that the caller will want to get to later
460 * on. The inode.i_private pointer will point to this value on
462 * @fops: a pointer to a struct file_operations that should be used for
465 * This is the basic "create a file" function for tracefs. It allows for a
466 * wide range of flexibility in creating a file, or a directory (if you want
467 * to create a directory, the tracefs_create_dir() function is
468 * recommended to be used instead.)
470 * This function will return a pointer to a dentry if it succeeds. This
471 * pointer must be passed to the tracefs_remove() function when the file is
472 * to be removed (no automatic cleanup happens if your module is unloaded,
473 * you are responsible here.) If an error occurs, %NULL will be returned.
475 * If tracefs is not enabled in the kernel, the value -%ENODEV will be
478 struct dentry *tracefs_create_file(const char *name, umode_t mode,
479 struct dentry *parent, void *data,
480 const struct file_operations *fops)
482 struct dentry *dentry;
485 if (security_locked_down(LOCKDOWN_TRACEFS))
488 if (!(mode & S_IFMT))
490 BUG_ON(!S_ISREG(mode));
491 dentry = start_creating(name, parent);
496 inode = tracefs_get_inode(dentry->d_sb);
497 if (unlikely(!inode))
498 return failed_creating(dentry);
500 inode->i_mode = mode;
501 inode->i_fop = fops ? fops : &tracefs_file_operations;
502 inode->i_private = data;
503 inode->i_uid = d_inode(dentry->d_parent)->i_uid;
504 inode->i_gid = d_inode(dentry->d_parent)->i_gid;
505 d_instantiate(dentry, inode);
506 fsnotify_create(dentry->d_parent->d_inode, dentry);
507 return end_creating(dentry);
510 static struct dentry *__create_dir(const char *name, struct dentry *parent,
511 const struct inode_operations *ops)
513 struct dentry *dentry = start_creating(name, parent);
519 inode = tracefs_get_inode(dentry->d_sb);
520 if (unlikely(!inode))
521 return failed_creating(dentry);
523 /* Do not set bits for OTH */
524 inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
526 inode->i_fop = &simple_dir_operations;
527 inode->i_uid = d_inode(dentry->d_parent)->i_uid;
528 inode->i_gid = d_inode(dentry->d_parent)->i_gid;
530 /* directory inodes start off with i_nlink == 2 (for "." entry) */
532 d_instantiate(dentry, inode);
533 inc_nlink(dentry->d_parent->d_inode);
534 fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
535 return end_creating(dentry);
539 * tracefs_create_dir - create a directory in the tracefs filesystem
540 * @name: a pointer to a string containing the name of the directory to
542 * @parent: a pointer to the parent dentry for this file. This should be a
543 * directory dentry if set. If this parameter is NULL, then the
544 * directory will be created in the root of the tracefs filesystem.
546 * This function creates a directory in tracefs with the given name.
548 * This function will return a pointer to a dentry if it succeeds. This
549 * pointer must be passed to the tracefs_remove() function when the file is
550 * to be removed. If an error occurs, %NULL will be returned.
552 * If tracing is not enabled in the kernel, the value -%ENODEV will be
555 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
557 if (security_locked_down(LOCKDOWN_TRACEFS))
560 return __create_dir(name, parent, &simple_dir_inode_operations);
564 * tracefs_create_instance_dir - create the tracing instances directory
565 * @name: The name of the instances directory to create
566 * @parent: The parent directory that the instances directory will exist
567 * @mkdir: The function to call when a mkdir is performed.
568 * @rmdir: The function to call when a rmdir is performed.
570 * Only one instances directory is allowed.
572 * The instances directory is special as it allows for mkdir and rmdir to
573 * to be done by userspace. When a mkdir or rmdir is performed, the inode
574 * locks are released and the methhods passed in (@mkdir and @rmdir) are
575 * called without locks and with the name of the directory being created
576 * within the instances directory.
578 * Returns the dentry of the instances directory.
580 __init struct dentry *tracefs_create_instance_dir(const char *name,
581 struct dentry *parent,
582 int (*mkdir)(const char *name),
583 int (*rmdir)(const char *name))
585 struct dentry *dentry;
587 /* Only allow one instance of the instances directory. */
588 if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
591 dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
595 tracefs_ops.mkdir = mkdir;
596 tracefs_ops.rmdir = rmdir;
601 static void remove_one(struct dentry *victim)
603 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
607 * tracefs_remove - recursively removes a directory
608 * @dentry: a pointer to a the dentry of the directory to be removed.
610 * This function recursively removes a directory tree in tracefs that
611 * was previously created with a call to another tracefs function
612 * (like tracefs_create_file() or variants thereof.)
614 void tracefs_remove(struct dentry *dentry)
616 if (IS_ERR_OR_NULL(dentry))
619 simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
620 simple_recursive_removal(dentry, remove_one);
621 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
625 * tracefs_initialized - Tells whether tracefs has been registered
627 bool tracefs_initialized(void)
629 return tracefs_registered;
632 static int __init tracefs_init(void)
636 retval = sysfs_create_mount_point(kernel_kobj, "tracing");
640 retval = register_filesystem(&trace_fs_type);
642 tracefs_registered = true;
646 core_initcall(tracefs_init);