1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * inode.c - part of tracefs, a pseudo file system for activating tracing
4 *
5 * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
6 *
7 * Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
8 *
9 * tracefs is the file system that is used by the tracing infrastructure.
10 */
11
12#include <linux/module.h>
13#include <linux/fs.h>
14#include <linux/fs_context.h>
15#include <linux/fs_parser.h>
16#include <linux/kobject.h>
17#include <linux/namei.h>
18#include <linux/tracefs.h>
19#include <linux/fsnotify.h>
20#include <linux/security.h>
21#include <linux/seq_file.h>
22#include <linux/magic.h>
23#include <linux/slab.h>
24#include "internal.h"
25
26#define TRACEFS_DEFAULT_MODE 0700
27static struct kmem_cache *tracefs_inode_cachep __ro_after_init;
28
29static struct vfsmount *tracefs_mount;
30static int tracefs_mount_count;
31static bool tracefs_registered;
32
33/*
34 * Keep track of all tracefs_inodes in order to update their
35 * flags if necessary on a remount.
36 */
37static DEFINE_SPINLOCK(tracefs_inode_lock);
38static LIST_HEAD(tracefs_inodes);
39
40static struct inode *tracefs_alloc_inode(struct super_block *sb)
41{
42 struct tracefs_inode *ti;
43 unsigned long flags;
44
45 ti = alloc_inode_sb(sb, tracefs_inode_cachep, GFP_KERNEL);
46 if (!ti)
47 return NULL;
48
49 spin_lock_irqsave(&tracefs_inode_lock, flags);
50 list_add_rcu(new: &ti->list, head: &tracefs_inodes);
51 spin_unlock_irqrestore(lock: &tracefs_inode_lock, flags);
52
53 return &ti->vfs_inode;
54}
55
56static void tracefs_free_inode(struct inode *inode)
57{
58 struct tracefs_inode *ti = get_tracefs(inode);
59
60 kmem_cache_free(s: tracefs_inode_cachep, objp: ti);
61}
62
63static void tracefs_destroy_inode(struct inode *inode)
64{
65 struct tracefs_inode *ti = get_tracefs(inode);
66 unsigned long flags;
67
68 spin_lock_irqsave(&tracefs_inode_lock, flags);
69 list_del_rcu(entry: &ti->list);
70 spin_unlock_irqrestore(lock: &tracefs_inode_lock, flags);
71}
72
73static ssize_t default_read_file(struct file *file, char __user *buf,
74 size_t count, loff_t *ppos)
75{
76 return 0;
77}
78
79static ssize_t default_write_file(struct file *file, const char __user *buf,
80 size_t count, loff_t *ppos)
81{
82 return count;
83}
84
85static const struct file_operations tracefs_file_operations = {
86 .read = default_read_file,
87 .write = default_write_file,
88 .open = simple_open,
89 .llseek = noop_llseek,
90};
91
92static struct tracefs_dir_ops {
93 int (*mkdir)(const char *name);
94 int (*rmdir)(const char *name);
95} tracefs_ops __ro_after_init;
96
97static char *get_dname(struct dentry *dentry)
98{
99 const char *dname;
100 char *name;
101 int len = dentry->d_name.len;
102
103 dname = dentry->d_name.name;
104 name = kmalloc(len + 1, GFP_KERNEL);
105 if (!name)
106 return NULL;
107 memcpy(name, dname, len);
108 name[len] = 0;
109 return name;
110}
111
112static struct dentry *tracefs_syscall_mkdir(struct mnt_idmap *idmap,
113 struct inode *inode, struct dentry *dentry,
114 umode_t mode)
115{
116 struct tracefs_inode *ti;
117 char *name;
118 int ret;
119
120 name = get_dname(dentry);
121 if (!name)
122 return ERR_PTR(error: -ENOMEM);
123
124 /*
125 * This is a new directory that does not take the default of
126 * the rootfs. It becomes the default permissions for all the
127 * files and directories underneath it.
128 */
129 ti = get_tracefs(inode);
130 ti->flags |= TRACEFS_INSTANCE_INODE;
131 ti->private = inode;
132
133 /*
134 * The mkdir call can call the generic functions that create
135 * the files within the tracefs system. It is up to the individual
136 * mkdir routine to handle races.
137 */
138 inode_unlock(inode);
139 ret = tracefs_ops.mkdir(name);
140 inode_lock(inode);
141
142 kfree(objp: name);
143
144 return ERR_PTR(error: ret);
145}
146
147static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
148{
149 char *name;
150 int ret;
151
152 name = get_dname(dentry);
153 if (!name)
154 return -ENOMEM;
155
156 /*
157 * The rmdir call can call the generic functions that create
158 * the files within the tracefs system. It is up to the individual
159 * rmdir routine to handle races.
160 * This time we need to unlock not only the parent (inode) but
161 * also the directory that is being deleted.
162 */
163 inode_unlock(inode);
164 inode_unlock(inode: d_inode(dentry));
165
166 ret = tracefs_ops.rmdir(name);
167
168 inode_lock_nested(inode, subclass: I_MUTEX_PARENT);
169 inode_lock(inode: d_inode(dentry));
170
171 kfree(objp: name);
172
173 return ret;
174}
175
176static void set_tracefs_inode_owner(struct inode *inode)
177{
178 struct tracefs_inode *ti = get_tracefs(inode);
179 struct inode *root_inode = ti->private;
180 kuid_t uid;
181 kgid_t gid;
182
183 uid = root_inode->i_uid;
184 gid = root_inode->i_gid;
185
186 /*
187 * If the root is not the mount point, then check the root's
188 * permissions. If it was never set, then default to the
189 * mount point.
190 */
191 if (root_inode != d_inode(dentry: root_inode->i_sb->s_root)) {
192 struct tracefs_inode *rti;
193
194 rti = get_tracefs(inode: root_inode);
195 root_inode = d_inode(dentry: root_inode->i_sb->s_root);
196
197 if (!(rti->flags & TRACEFS_UID_PERM_SET))
198 uid = root_inode->i_uid;
199
200 if (!(rti->flags & TRACEFS_GID_PERM_SET))
201 gid = root_inode->i_gid;
202 }
203
204 /*
205 * If this inode has never been referenced, then update
206 * the permissions to the superblock.
207 */
208 if (!(ti->flags & TRACEFS_UID_PERM_SET))
209 inode->i_uid = uid;
210
211 if (!(ti->flags & TRACEFS_GID_PERM_SET))
212 inode->i_gid = gid;
213}
214
215static int tracefs_permission(struct mnt_idmap *idmap,
216 struct inode *inode, int mask)
217{
218 set_tracefs_inode_owner(inode);
219 return generic_permission(idmap, inode, mask);
220}
221
222static int tracefs_getattr(struct mnt_idmap *idmap,
223 const struct path *path, struct kstat *stat,
224 u32 request_mask, unsigned int flags)
225{
226 struct inode *inode = d_backing_inode(upper: path->dentry);
227
228 set_tracefs_inode_owner(inode);
229 generic_fillattr(idmap, request_mask, inode, stat);
230 return 0;
231}
232
233static int tracefs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
234 struct iattr *attr)
235{
236 unsigned int ia_valid = attr->ia_valid;
237 struct inode *inode = d_inode(dentry);
238 struct tracefs_inode *ti = get_tracefs(inode);
239
240 if (ia_valid & ATTR_UID)
241 ti->flags |= TRACEFS_UID_PERM_SET;
242
243 if (ia_valid & ATTR_GID)
244 ti->flags |= TRACEFS_GID_PERM_SET;
245
246 return simple_setattr(idmap, dentry, attr);
247}
248
249static const struct inode_operations tracefs_instance_dir_inode_operations = {
250 .lookup = simple_lookup,
251 .mkdir = tracefs_syscall_mkdir,
252 .rmdir = tracefs_syscall_rmdir,
253 .permission = tracefs_permission,
254 .getattr = tracefs_getattr,
255 .setattr = tracefs_setattr,
256};
257
258static const struct inode_operations tracefs_dir_inode_operations = {
259 .lookup = simple_lookup,
260 .permission = tracefs_permission,
261 .getattr = tracefs_getattr,
262 .setattr = tracefs_setattr,
263};
264
265static const struct inode_operations tracefs_file_inode_operations = {
266 .permission = tracefs_permission,
267 .getattr = tracefs_getattr,
268 .setattr = tracefs_setattr,
269};
270
271struct inode *tracefs_get_inode(struct super_block *sb)
272{
273 struct inode *inode = new_inode(sb);
274 if (inode) {
275 inode->i_ino = get_next_ino();
276 simple_inode_init_ts(inode);
277 }
278 return inode;
279}
280
281struct tracefs_fs_info {
282 kuid_t uid;
283 kgid_t gid;
284 umode_t mode;
285 /* Opt_* bitfield. */
286 unsigned int opts;
287};
288
289enum {
290 Opt_uid,
291 Opt_gid,
292 Opt_mode,
293};
294
295static const struct fs_parameter_spec tracefs_param_specs[] = {
296 fsparam_gid ("gid", Opt_gid),
297 fsparam_u32oct ("mode", Opt_mode),
298 fsparam_uid ("uid", Opt_uid),
299 {}
300};
301
302static int tracefs_parse_param(struct fs_context *fc, struct fs_parameter *param)
303{
304 struct tracefs_fs_info *opts = fc->s_fs_info;
305 struct fs_parse_result result;
306 int opt;
307
308 opt = fs_parse(fc, desc: tracefs_param_specs, param, result: &result);
309 if (opt < 0)
310 return opt;
311
312 switch (opt) {
313 case Opt_uid:
314 opts->uid = result.uid;
315 break;
316 case Opt_gid:
317 opts->gid = result.gid;
318 break;
319 case Opt_mode:
320 opts->mode = result.uint_32 & S_IALLUGO;
321 break;
322 /*
323 * We might like to report bad mount options here;
324 * but traditionally tracefs has ignored all mount options
325 */
326 }
327
328 opts->opts |= BIT(opt);
329
330 return 0;
331}
332
333static int tracefs_apply_options(struct super_block *sb, bool remount)
334{
335 struct tracefs_fs_info *fsi = sb->s_fs_info;
336 struct inode *inode = d_inode(dentry: sb->s_root);
337 struct tracefs_inode *ti;
338 bool update_uid, update_gid;
339 umode_t tmp_mode;
340
341 /*
342 * On remount, only reset mode/uid/gid if they were provided as mount
343 * options.
344 */
345
346 if (!remount || fsi->opts & BIT(Opt_mode)) {
347 tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
348 tmp_mode |= fsi->mode;
349 WRITE_ONCE(inode->i_mode, tmp_mode);
350 }
351
352 if (!remount || fsi->opts & BIT(Opt_uid))
353 inode->i_uid = fsi->uid;
354
355 if (!remount || fsi->opts & BIT(Opt_gid))
356 inode->i_gid = fsi->gid;
357
358 if (remount && (fsi->opts & BIT(Opt_uid) || fsi->opts & BIT(Opt_gid))) {
359
360 update_uid = fsi->opts & BIT(Opt_uid);
361 update_gid = fsi->opts & BIT(Opt_gid);
362
363 rcu_read_lock();
364 list_for_each_entry_rcu(ti, &tracefs_inodes, list) {
365 if (update_uid) {
366 ti->flags &= ~TRACEFS_UID_PERM_SET;
367 ti->vfs_inode.i_uid = fsi->uid;
368 }
369
370 if (update_gid) {
371 ti->flags &= ~TRACEFS_GID_PERM_SET;
372 ti->vfs_inode.i_gid = fsi->gid;
373 }
374
375 /*
376 * Note, the above ti->vfs_inode updates are
377 * used in eventfs_remount() so they must come
378 * before calling it.
379 */
380 if (ti->flags & TRACEFS_EVENT_INODE)
381 eventfs_remount(ti, update_uid, update_gid);
382 }
383 rcu_read_unlock();
384 }
385
386 return 0;
387}
388
389static int tracefs_reconfigure(struct fs_context *fc)
390{
391 struct super_block *sb = fc->root->d_sb;
392 struct tracefs_fs_info *sb_opts = sb->s_fs_info;
393 struct tracefs_fs_info *new_opts = fc->s_fs_info;
394
395 if (!new_opts)
396 return 0;
397
398 sync_filesystem(sb);
399 /* structure copy of new mount options to sb */
400 *sb_opts = *new_opts;
401
402 return tracefs_apply_options(sb, remount: true);
403}
404
405static int tracefs_show_options(struct seq_file *m, struct dentry *root)
406{
407 struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
408
409 if (!uid_eq(left: fsi->uid, GLOBAL_ROOT_UID))
410 seq_printf(m, ",uid=%u",
411 from_kuid_munged(&init_user_ns, fsi->uid));
412 if (!gid_eq(fsi->gid, GLOBAL_ROOT_GID))
413 seq_printf(m, ",gid=%u",
414 from_kgid_munged(&init_user_ns, fsi->gid));
415 if (fsi->mode != TRACEFS_DEFAULT_MODE)
416 seq_printf(m, ",mode=%o", fsi->mode);
417
418 return 0;
419}
420
421static int tracefs_drop_inode(struct inode *inode)
422{
423 struct tracefs_inode *ti = get_tracefs(inode);
424
425 /*
426 * This inode is being freed and cannot be used for
427 * eventfs. Clear the flag so that it doesn't call into
428 * eventfs during the remount flag updates. The eventfs_inode
429 * gets freed after an RCU cycle, so the content will still
430 * be safe if the iteration is going on now.
431 */
432 ti->flags &= ~TRACEFS_EVENT_INODE;
433
434 return 1;
435}
436
437static const struct super_operations tracefs_super_operations = {
438 .alloc_inode = tracefs_alloc_inode,
439 .free_inode = tracefs_free_inode,
440 .destroy_inode = tracefs_destroy_inode,
441 .drop_inode = tracefs_drop_inode,
442 .statfs = simple_statfs,
443 .show_options = tracefs_show_options,
444};
445
446/*
447 * It would be cleaner if eventfs had its own dentry ops.
448 *
449 * Note that d_revalidate is called potentially under RCU,
450 * so it can't take the eventfs mutex etc. It's fine - if
451 * we open a file just as it's marked dead, things will
452 * still work just fine, and just see the old stale case.
453 */
454static void tracefs_d_release(struct dentry *dentry)
455{
456 if (dentry->d_fsdata)
457 eventfs_d_release(dentry);
458}
459
460static int tracefs_d_revalidate(struct inode *inode, const struct qstr *name,
461 struct dentry *dentry, unsigned int flags)
462{
463 struct eventfs_inode *ei = dentry->d_fsdata;
464
465 return !(ei && ei->is_freed);
466}
467
468static int tracefs_d_delete(const struct dentry *dentry)
469{
470 /*
471 * We want to keep eventfs dentries around but not tracefs
472 * ones. eventfs dentries have content in d_fsdata.
473 * Use d_fsdata to determine if it's a eventfs dentry or not.
474 */
475 return dentry->d_fsdata == NULL;
476}
477
478static const struct dentry_operations tracefs_dentry_operations = {
479 .d_revalidate = tracefs_d_revalidate,
480 .d_release = tracefs_d_release,
481 .d_delete = tracefs_d_delete,
482};
483
484static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
485{
486 static const struct tree_descr trace_files[] = {{""}};
487 int err;
488
489 err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
490 if (err)
491 return err;
492
493 sb->s_op = &tracefs_super_operations;
494 set_default_d_op(sb, &tracefs_dentry_operations);
495
496 return 0;
497}
498
499static int tracefs_get_tree(struct fs_context *fc)
500{
501 int err = get_tree_single(fc, fill_super: tracefs_fill_super);
502
503 if (err)
504 return err;
505
506 return tracefs_reconfigure(fc);
507}
508
509static void tracefs_free_fc(struct fs_context *fc)
510{
511 kfree(objp: fc->s_fs_info);
512}
513
514static const struct fs_context_operations tracefs_context_ops = {
515 .free = tracefs_free_fc,
516 .parse_param = tracefs_parse_param,
517 .get_tree = tracefs_get_tree,
518 .reconfigure = tracefs_reconfigure,
519};
520
521static int tracefs_init_fs_context(struct fs_context *fc)
522{
523 struct tracefs_fs_info *fsi;
524
525 fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
526 if (!fsi)
527 return -ENOMEM;
528
529 fsi->mode = TRACEFS_DEFAULT_MODE;
530
531 fc->s_fs_info = fsi;
532 fc->ops = &tracefs_context_ops;
533 return 0;
534}
535
536static struct file_system_type trace_fs_type = {
537 .owner = THIS_MODULE,
538 .name = "tracefs",
539 .init_fs_context = tracefs_init_fs_context,
540 .parameters = tracefs_param_specs,
541 .kill_sb = kill_anon_super,
542};
543MODULE_ALIAS_FS("tracefs");
544
545struct dentry *tracefs_start_creating(const char *name, struct dentry *parent)
546{
547 struct dentry *dentry;
548 int error;
549
550 pr_debug("tracefs: creating file '%s'\n",name);
551
552 error = simple_pin_fs(&trace_fs_type, mount: &tracefs_mount,
553 count: &tracefs_mount_count);
554 if (error)
555 return ERR_PTR(error);
556
557 /* If the parent is not specified, we create it in the root.
558 * We need the root dentry to do this, which is in the super
559 * block. A pointer to that is in the struct vfsmount that we
560 * have around.
561 */
562 if (!parent)
563 parent = tracefs_mount->mnt_root;
564
565 dentry = simple_start_creating(parent, name);
566 if (IS_ERR(ptr: dentry))
567 simple_release_fs(mount: &tracefs_mount, count: &tracefs_mount_count);
568
569 return dentry;
570}
571
572struct dentry *tracefs_failed_creating(struct dentry *dentry)
573{
574 simple_done_creating(dentry);
575 simple_release_fs(mount: &tracefs_mount, count: &tracefs_mount_count);
576 return NULL;
577}
578
579struct dentry *tracefs_end_creating(struct dentry *dentry)
580{
581 simple_done_creating(dentry);
582 return dentry; // borrowed
583}
584
585/* Find the inode that this will use for default */
586static struct inode *instance_inode(struct dentry *parent, struct inode *inode)
587{
588 struct tracefs_inode *ti;
589
590 /* If parent is NULL then use root inode */
591 if (!parent)
592 return d_inode(dentry: inode->i_sb->s_root);
593
594 /* Find the inode that is flagged as an instance or the root inode */
595 while (!IS_ROOT(parent)) {
596 ti = get_tracefs(inode: d_inode(dentry: parent));
597 if (ti->flags & TRACEFS_INSTANCE_INODE)
598 break;
599 parent = parent->d_parent;
600 }
601
602 return d_inode(dentry: parent);
603}
604
605/**
606 * tracefs_create_file - create a file in the tracefs filesystem
607 * @name: a pointer to a string containing the name of the file to create.
608 * @mode: the permission that the file should have.
609 * @parent: a pointer to the parent dentry for this file. This should be a
610 * directory dentry if set. If this parameter is NULL, then the
611 * file will be created in the root of the tracefs filesystem.
612 * @data: a pointer to something that the caller will want to get to later
613 * on. The inode.i_private pointer will point to this value on
614 * the open() call.
615 * @fops: a pointer to a struct file_operations that should be used for
616 * this file.
617 *
618 * This is the basic "create a file" function for tracefs. It allows for a
619 * wide range of flexibility in creating a file, or a directory (if you want
620 * to create a directory, the tracefs_create_dir() function is
621 * recommended to be used instead.)
622 *
623 * This function will return a pointer to a dentry if it succeeds. This
624 * pointer must be passed to the tracefs_remove() function when the file is
625 * to be removed (no automatic cleanup happens if your module is unloaded,
626 * you are responsible here.) If an error occurs, %NULL will be returned.
627 *
628 * If tracefs is not enabled in the kernel, the value -%ENODEV will be
629 * returned.
630 */
631struct dentry *tracefs_create_file(const char *name, umode_t mode,
632 struct dentry *parent, void *data,
633 const struct file_operations *fops)
634{
635 struct tracefs_inode *ti;
636 struct dentry *dentry;
637 struct inode *inode;
638
639 if (security_locked_down(what: LOCKDOWN_TRACEFS))
640 return NULL;
641
642 if (!(mode & S_IFMT))
643 mode |= S_IFREG;
644 BUG_ON(!S_ISREG(mode));
645 dentry = tracefs_start_creating(name, parent);
646
647 if (IS_ERR(ptr: dentry))
648 return NULL;
649
650 inode = tracefs_get_inode(sb: dentry->d_sb);
651 if (unlikely(!inode))
652 return tracefs_failed_creating(dentry);
653
654 ti = get_tracefs(inode);
655 ti->private = instance_inode(parent, inode);
656
657 inode->i_mode = mode;
658 inode->i_op = &tracefs_file_inode_operations;
659 inode->i_fop = fops ? fops : &tracefs_file_operations;
660 inode->i_private = data;
661 inode->i_uid = d_inode(dentry: dentry->d_parent)->i_uid;
662 inode->i_gid = d_inode(dentry: dentry->d_parent)->i_gid;
663 d_make_persistent(dentry, inode);
664 fsnotify_create(dir: d_inode(dentry: dentry->d_parent), dentry);
665 return tracefs_end_creating(dentry);
666}
667
668static struct dentry *__create_dir(const char *name, struct dentry *parent,
669 const struct inode_operations *ops)
670{
671 struct tracefs_inode *ti;
672 struct dentry *dentry = tracefs_start_creating(name, parent);
673 struct inode *inode;
674
675 if (IS_ERR(ptr: dentry))
676 return NULL;
677
678 inode = tracefs_get_inode(sb: dentry->d_sb);
679 if (unlikely(!inode))
680 return tracefs_failed_creating(dentry);
681
682 /* Do not set bits for OTH */
683 inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
684 inode->i_op = ops;
685 inode->i_fop = &simple_dir_operations;
686 inode->i_uid = d_inode(dentry: dentry->d_parent)->i_uid;
687 inode->i_gid = d_inode(dentry: dentry->d_parent)->i_gid;
688
689 ti = get_tracefs(inode);
690 ti->private = instance_inode(parent, inode);
691
692 /* directory inodes start off with i_nlink == 2 (for "." entry) */
693 inc_nlink(inode);
694 d_make_persistent(dentry, inode);
695 inc_nlink(inode: d_inode(dentry: dentry->d_parent));
696 fsnotify_mkdir(dir: d_inode(dentry: dentry->d_parent), dentry);
697 return tracefs_end_creating(dentry);
698}
699
700/**
701 * tracefs_create_dir - create a directory in the tracefs filesystem
702 * @name: a pointer to a string containing the name of the directory to
703 * create.
704 * @parent: a pointer to the parent dentry for this file. This should be a
705 * directory dentry if set. If this parameter is NULL, then the
706 * directory will be created in the root of the tracefs filesystem.
707 *
708 * This function creates a directory in tracefs with the given name.
709 *
710 * This function will return a pointer to a dentry if it succeeds. This
711 * pointer must be passed to the tracefs_remove() function when the file is
712 * to be removed. If an error occurs, %NULL will be returned.
713 *
714 * If tracing is not enabled in the kernel, the value -%ENODEV will be
715 * returned.
716 */
717struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
718{
719 if (security_locked_down(what: LOCKDOWN_TRACEFS))
720 return NULL;
721
722 return __create_dir(name, parent, ops: &tracefs_dir_inode_operations);
723}
724
725/**
726 * tracefs_create_instance_dir - create the tracing instances directory
727 * @name: The name of the instances directory to create
728 * @parent: The parent directory that the instances directory will exist
729 * @mkdir: The function to call when a mkdir is performed.
730 * @rmdir: The function to call when a rmdir is performed.
731 *
732 * Only one instances directory is allowed.
733 *
734 * The instances directory is special as it allows for mkdir and rmdir
735 * to be done by userspace. When a mkdir or rmdir is performed, the inode
736 * locks are released and the methods passed in (@mkdir and @rmdir) are
737 * called without locks and with the name of the directory being created
738 * within the instances directory.
739 *
740 * Returns the dentry of the instances directory.
741 */
742__init struct dentry *tracefs_create_instance_dir(const char *name,
743 struct dentry *parent,
744 int (*mkdir)(const char *name),
745 int (*rmdir)(const char *name))
746{
747 struct dentry *dentry;
748
749 /* Only allow one instance of the instances directory. */
750 if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
751 return NULL;
752
753 dentry = __create_dir(name, parent, ops: &tracefs_instance_dir_inode_operations);
754 if (!dentry)
755 return NULL;
756
757 tracefs_ops.mkdir = mkdir;
758 tracefs_ops.rmdir = rmdir;
759
760 return dentry;
761}
762
763static void remove_one(struct dentry *victim)
764{
765 simple_release_fs(mount: &tracefs_mount, count: &tracefs_mount_count);
766}
767
768/**
769 * tracefs_remove - recursively removes a directory
770 * @dentry: a pointer to a the dentry of the directory to be removed.
771 *
772 * This function recursively removes a directory tree in tracefs that
773 * was previously created with a call to another tracefs function
774 * (like tracefs_create_file() or variants thereof.)
775 */
776void tracefs_remove(struct dentry *dentry)
777{
778 if (IS_ERR_OR_NULL(ptr: dentry))
779 return;
780
781 simple_pin_fs(&trace_fs_type, mount: &tracefs_mount, count: &tracefs_mount_count);
782 simple_recursive_removal(dentry, callback: remove_one);
783 simple_release_fs(mount: &tracefs_mount, count: &tracefs_mount_count);
784}
785
786/**
787 * tracefs_initialized - Tells whether tracefs has been registered
788 */
789bool tracefs_initialized(void)
790{
791 return tracefs_registered;
792}
793
794static void init_once(void *foo)
795{
796 struct tracefs_inode *ti = (struct tracefs_inode *) foo;
797
798 /* inode_init_once() calls memset() on the vfs_inode portion */
799 inode_init_once(&ti->vfs_inode);
800
801 /* Zero out the rest */
802 memset_after(ti, 0, vfs_inode);
803}
804
805static int __init tracefs_init(void)
806{
807 int retval;
808
809 tracefs_inode_cachep = kmem_cache_create("tracefs_inode_cache",
810 sizeof(struct tracefs_inode),
811 0, (SLAB_RECLAIM_ACCOUNT|
812 SLAB_ACCOUNT),
813 init_once);
814 if (!tracefs_inode_cachep)
815 return -ENOMEM;
816
817 retval = sysfs_create_mount_point(parent_kobj: kernel_kobj, name: "tracing");
818 if (retval)
819 return -EINVAL;
820
821 retval = register_filesystem(&trace_fs_type);
822 if (!retval)
823 tracefs_registered = true;
824
825 return retval;
826}
827core_initcall(tracefs_init);
828

source code of linux/fs/tracefs/inode.c