1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  inode.c - part of debugfs, a tiny little debug file system
  4 *
  5 *  Copyright (C) 2004,2019 Greg Kroah-Hartman <greg@kroah.com>
  6 *  Copyright (C) 2004 IBM Inc.
  7 *  Copyright (C) 2019 Linux Foundation <gregkh@linuxfoundation.org>
  8 *
  9 *  debugfs is for people to use instead of /proc or /sys.
 10 *  See ./Documentation/core-api/kernel-api.rst for more details.
 11 */
 12
 13#define pr_fmt(fmt)	"debugfs: " fmt
 14
 15#include <linux/module.h>
 16#include <linux/fs.h>
 17#include <linux/fs_context.h>
 18#include <linux/fs_parser.h>
 19#include <linux/pagemap.h>
 20#include <linux/init.h>
 21#include <linux/kobject.h>
 22#include <linux/namei.h>
 23#include <linux/debugfs.h>
 24#include <linux/fsnotify.h>
 25#include <linux/string.h>
 26#include <linux/seq_file.h>
 
 27#include <linux/magic.h>
 28#include <linux/slab.h>
 29#include <linux/security.h>
 30
 31#include "internal.h"
 32
 33#define DEBUGFS_DEFAULT_MODE	0700
 34
 35static struct vfsmount *debugfs_mount;
 36static int debugfs_mount_count;
 37static bool debugfs_registered;
 38static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS;
 39
 40/*
 41 * Don't allow access attributes to be changed whilst the kernel is locked down
 42 * so that we can use the file mode as part of a heuristic to determine whether
 43 * to lock down individual files.
 44 */
 45static int debugfs_setattr(struct mnt_idmap *idmap,
 46			   struct dentry *dentry, struct iattr *ia)
 47{
 48	int ret;
 49
 50	if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) {
 51		ret = security_locked_down(LOCKDOWN_DEBUGFS);
 52		if (ret)
 53			return ret;
 54	}
 55	return simple_setattr(&nop_mnt_idmap, dentry, ia);
 56}
 57
 58static const struct inode_operations debugfs_file_inode_operations = {
 59	.setattr	= debugfs_setattr,
 60};
 61static const struct inode_operations debugfs_dir_inode_operations = {
 62	.lookup		= simple_lookup,
 63	.setattr	= debugfs_setattr,
 64};
 65static const struct inode_operations debugfs_symlink_inode_operations = {
 66	.get_link	= simple_get_link,
 67	.setattr	= debugfs_setattr,
 68};
 69
 70static struct inode *debugfs_get_inode(struct super_block *sb)
 71{
 72	struct inode *inode = new_inode(sb);
 73	if (inode) {
 74		inode->i_ino = get_next_ino();
 75		simple_inode_init_ts(inode);
 
 76	}
 77	return inode;
 78}
 79
 80struct debugfs_fs_info {
 81	kuid_t uid;
 82	kgid_t gid;
 83	umode_t mode;
 84	/* Opt_* bitfield. */
 85	unsigned int opts;
 86};
 87
 88enum {
 89	Opt_uid,
 90	Opt_gid,
 91	Opt_mode,
 92	Opt_source,
 
 
 
 
 
 
 
 93};
 94
 95static const struct fs_parameter_spec debugfs_param_specs[] = {
 96	fsparam_gid	("gid",		Opt_gid),
 97	fsparam_u32oct	("mode",	Opt_mode),
 98	fsparam_uid	("uid",		Opt_uid),
 99	fsparam_string	("source",	Opt_source),
100	{}
101};
102
103static int debugfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
104{
105	struct debugfs_fs_info *opts = fc->s_fs_info;
106	struct fs_parse_result result;
107	int opt;
 
 
 
108
109	opt = fs_parse(fc, debugfs_param_specs, param, &result);
110	if (opt < 0) {
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
111		/*
112                * We might like to report bad mount options here; but
113                * traditionally debugfs has ignored all mount options
114                */
115		if (opt == -ENOPARAM)
116			return 0;
117
118		return opt;
119	}
120
121	switch (opt) {
122	case Opt_uid:
123		opts->uid = result.uid;
124		break;
125	case Opt_gid:
126		opts->gid = result.gid;
127		break;
128	case Opt_mode:
129		opts->mode = result.uint_32 & S_IALLUGO;
130		break;
131	case Opt_source:
132		if (fc->source)
133			return invalfc(fc, "Multiple sources specified");
134		fc->source = param->string;
135		param->string = NULL;
136		break;
137	/*
138	 * We might like to report bad mount options here;
139	 * but traditionally debugfs has ignored all mount options
140	 */
141	}
142
143	opts->opts |= BIT(opt);
144
145	return 0;
146}
147
148static void _debugfs_apply_options(struct super_block *sb, bool remount)
149{
150	struct debugfs_fs_info *fsi = sb->s_fs_info;
151	struct inode *inode = d_inode(sb->s_root);
 
152
153	/*
154	 * On remount, only reset mode/uid/gid if they were provided as mount
155	 * options.
156	 */
157
158	if (!remount || fsi->opts & BIT(Opt_mode)) {
159		inode->i_mode &= ~S_IALLUGO;
160		inode->i_mode |= fsi->mode;
161	}
162
163	if (!remount || fsi->opts & BIT(Opt_uid))
164		inode->i_uid = fsi->uid;
165
166	if (!remount || fsi->opts & BIT(Opt_gid))
167		inode->i_gid = fsi->gid;
168}
169
170static void debugfs_apply_options(struct super_block *sb)
171{
172	_debugfs_apply_options(sb, false);
173}
174
175static void debugfs_apply_options_remount(struct super_block *sb)
176{
177	_debugfs_apply_options(sb, true);
178}
179
180static int debugfs_reconfigure(struct fs_context *fc)
181{
182	struct super_block *sb = fc->root->d_sb;
183	struct debugfs_fs_info *sb_opts = sb->s_fs_info;
184	struct debugfs_fs_info *new_opts = fc->s_fs_info;
185
186	sync_filesystem(sb);
 
 
 
187
188	/* structure copy of new mount options to sb */
189	*sb_opts = *new_opts;
190	debugfs_apply_options_remount(sb);
191
192	return 0;
 
193}
194
195static int debugfs_show_options(struct seq_file *m, struct dentry *root)
196{
197	struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
 
198
199	if (!uid_eq(fsi->uid, GLOBAL_ROOT_UID))
200		seq_printf(m, ",uid=%u",
201			   from_kuid_munged(&init_user_ns, fsi->uid));
202	if (!gid_eq(fsi->gid, GLOBAL_ROOT_GID))
203		seq_printf(m, ",gid=%u",
204			   from_kgid_munged(&init_user_ns, fsi->gid));
205	if (fsi->mode != DEBUGFS_DEFAULT_MODE)
206		seq_printf(m, ",mode=%o", fsi->mode);
207
208	return 0;
209}
210
211static void debugfs_free_inode(struct inode *inode)
212{
213	if (S_ISLNK(inode->i_mode))
214		kfree(inode->i_link);
215	free_inode_nonrcu(inode);
216}
217
218static const struct super_operations debugfs_super_operations = {
219	.statfs		= simple_statfs,
 
220	.show_options	= debugfs_show_options,
221	.free_inode	= debugfs_free_inode,
222};
223
224static void debugfs_release_dentry(struct dentry *dentry)
225{
226	struct debugfs_fsdata *fsd = dentry->d_fsdata;
227
228	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
229		return;
230
231	/* check it wasn't a dir (no fsdata) or automount (no real_fops) */
232	if (fsd && (fsd->real_fops || fsd->short_fops)) {
233		WARN_ON(!list_empty(&fsd->cancellations));
234		mutex_destroy(&fsd->cancellations_mtx);
235	}
236
237	kfree(fsd);
238}
239
240static struct vfsmount *debugfs_automount(struct path *path)
241{
242	struct debugfs_fsdata *fsd = path->dentry->d_fsdata;
243
244	return fsd->automount(path->dentry, d_inode(path->dentry)->i_private);
245}
246
247static const struct dentry_operations debugfs_dops = {
248	.d_delete = always_delete_dentry,
249	.d_release = debugfs_release_dentry,
250	.d_automount = debugfs_automount,
251};
252
253static int debugfs_fill_super(struct super_block *sb, struct fs_context *fc)
254{
255	static const struct tree_descr debug_files[] = {{""}};
 
256	int err;
257
258	err = simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
 
 
 
 
 
 
 
259	if (err)
260		return err;
 
 
 
 
261
262	sb->s_op = &debugfs_super_operations;
263	sb->s_d_op = &debugfs_dops;
264
265	debugfs_apply_options(sb);
266
267	return 0;
268}
269
270static int debugfs_get_tree(struct fs_context *fc)
271{
272	if (!(debugfs_allow & DEBUGFS_ALLOW_API))
273		return -EPERM;
274
275	return get_tree_single(fc, debugfs_fill_super);
276}
277
278static void debugfs_free_fc(struct fs_context *fc)
279{
280	kfree(fc->s_fs_info);
 
281}
282
283static const struct fs_context_operations debugfs_context_ops = {
284	.free		= debugfs_free_fc,
285	.parse_param	= debugfs_parse_param,
286	.get_tree	= debugfs_get_tree,
287	.reconfigure	= debugfs_reconfigure,
288};
289
290static int debugfs_init_fs_context(struct fs_context *fc)
291{
292	struct debugfs_fs_info *fsi;
293
294	fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
295	if (!fsi)
296		return -ENOMEM;
297
298	fsi->mode = DEBUGFS_DEFAULT_MODE;
299
300	fc->s_fs_info = fsi;
301	fc->ops = &debugfs_context_ops;
302	return 0;
303}
304
305static struct file_system_type debug_fs_type = {
306	.owner =	THIS_MODULE,
307	.name =		"debugfs",
308	.init_fs_context = debugfs_init_fs_context,
309	.parameters =	debugfs_param_specs,
310	.kill_sb =	kill_litter_super,
311};
312MODULE_ALIAS_FS("debugfs");
313
314/**
315 * debugfs_lookup() - look up an existing debugfs file
316 * @name: a pointer to a string containing the name of the file to look up.
317 * @parent: a pointer to the parent dentry of the file.
318 *
319 * This function will return a pointer to a dentry if it succeeds.  If the file
320 * doesn't exist or an error occurs, %NULL will be returned.  The returned
321 * dentry must be passed to dput() when it is no longer needed.
322 *
323 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
324 * returned.
325 */
326struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
327{
328	struct dentry *dentry;
329
330	if (!debugfs_initialized() || IS_ERR_OR_NULL(name) || IS_ERR(parent))
331		return NULL;
332
333	if (!parent)
334		parent = debugfs_mount->mnt_root;
335
336	dentry = lookup_positive_unlocked(name, parent, strlen(name));
337	if (IS_ERR(dentry))
338		return NULL;
339	return dentry;
340}
341EXPORT_SYMBOL_GPL(debugfs_lookup);
342
343static struct dentry *start_creating(const char *name, struct dentry *parent)
344{
345	struct dentry *dentry;
346	int error;
347
348	if (!(debugfs_allow & DEBUGFS_ALLOW_API))
349		return ERR_PTR(-EPERM);
350
351	if (!debugfs_initialized())
352		return ERR_PTR(-ENOENT);
353
354	pr_debug("creating file '%s'\n", name);
355
356	if (IS_ERR(parent))
357		return parent;
358
359	error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
360			      &debugfs_mount_count);
361	if (error) {
362		pr_err("Unable to pin filesystem for file '%s'\n", name);
363		return ERR_PTR(error);
364	}
365
366	/* If the parent is not specified, we create it in the root.
367	 * We need the root dentry to do this, which is in the super
368	 * block. A pointer to that is in the struct vfsmount that we
369	 * have around.
370	 */
371	if (!parent)
372		parent = debugfs_mount->mnt_root;
373
374	inode_lock(d_inode(parent));
375	if (unlikely(IS_DEADDIR(d_inode(parent))))
376		dentry = ERR_PTR(-ENOENT);
377	else
378		dentry = lookup_one_len(name, parent, strlen(name));
379	if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
380		if (d_is_dir(dentry))
381			pr_err("Directory '%s' with parent '%s' already present!\n",
382			       name, parent->d_name.name);
383		else
384			pr_err("File '%s' in directory '%s' already present!\n",
385			       name, parent->d_name.name);
386		dput(dentry);
387		dentry = ERR_PTR(-EEXIST);
388	}
389
390	if (IS_ERR(dentry)) {
391		inode_unlock(d_inode(parent));
392		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
393	}
394
395	return dentry;
396}
397
398static struct dentry *failed_creating(struct dentry *dentry)
399{
400	inode_unlock(d_inode(dentry->d_parent));
401	dput(dentry);
402	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
403	return ERR_PTR(-ENOMEM);
404}
405
406static struct dentry *end_creating(struct dentry *dentry)
407{
408	inode_unlock(d_inode(dentry->d_parent));
409	return dentry;
410}
411
412static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
413				struct dentry *parent, void *data,
414				const struct file_operations *proxy_fops,
415				const void *real_fops)
416{
417	struct dentry *dentry;
418	struct inode *inode;
419
420	if (!(mode & S_IFMT))
421		mode |= S_IFREG;
422	BUG_ON(!S_ISREG(mode));
423	dentry = start_creating(name, parent);
424
425	if (IS_ERR(dentry))
426		return dentry;
427
428	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
429		failed_creating(dentry);
430		return ERR_PTR(-EPERM);
431	}
432
433	inode = debugfs_get_inode(dentry->d_sb);
434	if (unlikely(!inode)) {
435		pr_err("out of free dentries, can not create file '%s'\n",
436		       name);
437		return failed_creating(dentry);
438	}
439
440	inode->i_mode = mode;
441	inode->i_private = data;
442
443	inode->i_op = &debugfs_file_inode_operations;
444	inode->i_fop = proxy_fops;
445	dentry->d_fsdata = (void *)((unsigned long)real_fops |
446				DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
447
448	d_instantiate(dentry, inode);
449	fsnotify_create(d_inode(dentry->d_parent), dentry);
450	return end_creating(dentry);
451}
452
453struct dentry *debugfs_create_file_full(const char *name, umode_t mode,
454					struct dentry *parent, void *data,
455					const struct file_operations *fops)
456{
457	if (WARN_ON((unsigned long)fops &
458		    DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
459		return ERR_PTR(-EINVAL);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
460
461	return __debugfs_create_file(name, mode, parent, data,
462				fops ? &debugfs_full_proxy_file_operations :
463					&debugfs_noop_file_operations,
464				fops);
465}
466EXPORT_SYMBOL_GPL(debugfs_create_file_full);
467
468struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
469					 struct dentry *parent, void *data,
470					 const struct debugfs_short_fops *fops)
471{
472	if (WARN_ON((unsigned long)fops &
473		    DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
474		return ERR_PTR(-EINVAL);
475
476	return __debugfs_create_file(name, mode, parent, data,
477				fops ? &debugfs_full_short_proxy_file_operations :
478					&debugfs_noop_file_operations,
479				fops);
480}
481EXPORT_SYMBOL_GPL(debugfs_create_file_short);
482
483/**
484 * debugfs_create_file_unsafe - create a file in the debugfs filesystem
485 * @name: a pointer to a string containing the name of the file to create.
486 * @mode: the permission that the file should have.
487 * @parent: a pointer to the parent dentry for this file.  This should be a
488 *          directory dentry if set.  If this parameter is NULL, then the
489 *          file will be created in the root of the debugfs filesystem.
490 * @data: a pointer to something that the caller will want to get to later
491 *        on.  The inode.i_private pointer will point to this value on
492 *        the open() call.
493 * @fops: a pointer to a struct file_operations that should be used for
494 *        this file.
495 *
496 * debugfs_create_file_unsafe() is completely analogous to
497 * debugfs_create_file(), the only difference being that the fops
498 * handed it will not get protected against file removals by the
499 * debugfs core.
500 *
501 * It is your responsibility to protect your struct file_operation
502 * methods against file removals by means of debugfs_file_get()
503 * and debugfs_file_put(). ->open() is still protected by
504 * debugfs though.
505 *
506 * Any struct file_operations defined by means of
507 * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and
508 * thus, may be used here.
509 */
510struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
511				   struct dentry *parent, void *data,
512				   const struct file_operations *fops)
513{
514
515	return __debugfs_create_file(name, mode, parent, data,
516				fops ? &debugfs_open_proxy_file_operations :
517					&debugfs_noop_file_operations,
518				fops);
519}
520EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
521
522/**
523 * debugfs_create_file_size - create a file in the debugfs filesystem
524 * @name: a pointer to a string containing the name of the file to create.
525 * @mode: the permission that the file should have.
526 * @parent: a pointer to the parent dentry for this file.  This should be a
527 *          directory dentry if set.  If this parameter is NULL, then the
528 *          file will be created in the root of the debugfs filesystem.
529 * @data: a pointer to something that the caller will want to get to later
530 *        on.  The inode.i_private pointer will point to this value on
531 *        the open() call.
532 * @fops: a pointer to a struct file_operations that should be used for
533 *        this file.
534 * @file_size: initial file size
535 *
536 * This is the basic "create a file" function for debugfs.  It allows for a
537 * wide range of flexibility in creating a file, or a directory (if you want
538 * to create a directory, the debugfs_create_dir() function is
539 * recommended to be used instead.)
540 */
541void debugfs_create_file_size(const char *name, umode_t mode,
542			      struct dentry *parent, void *data,
543			      const struct file_operations *fops,
544			      loff_t file_size)
545{
546	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
547
548	if (!IS_ERR(de))
549		d_inode(de)->i_size = file_size;
550}
551EXPORT_SYMBOL_GPL(debugfs_create_file_size);
552
553/**
554 * debugfs_create_dir - create a directory in the debugfs filesystem
555 * @name: a pointer to a string containing the name of the directory to
556 *        create.
557 * @parent: a pointer to the parent dentry for this file.  This should be a
558 *          directory dentry if set.  If this parameter is NULL, then the
559 *          directory will be created in the root of the debugfs filesystem.
560 *
561 * This function creates a directory in debugfs with the given name.
562 *
563 * This function will return a pointer to a dentry if it succeeds.  This
564 * pointer must be passed to the debugfs_remove() function when the file is
565 * to be removed (no automatic cleanup happens if your module is unloaded,
566 * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
567 * returned.
568 *
569 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
570 * returned.
571 *
572 * NOTE: it's expected that most callers should _ignore_ the errors returned
573 * by this function. Other debugfs functions handle the fact that the "dentry"
574 * passed to them could be an error and they don't crash in that case.
575 * Drivers should generally work fine even if debugfs fails to init anyway.
576 */
577struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
578{
579	struct dentry *dentry = start_creating(name, parent);
580	struct inode *inode;
581
582	if (IS_ERR(dentry))
583		return dentry;
584
585	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
586		failed_creating(dentry);
587		return ERR_PTR(-EPERM);
588	}
589
590	inode = debugfs_get_inode(dentry->d_sb);
591	if (unlikely(!inode)) {
592		pr_err("out of free dentries, can not create directory '%s'\n",
593		       name);
594		return failed_creating(dentry);
595	}
596
597	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
598	inode->i_op = &debugfs_dir_inode_operations;
599	inode->i_fop = &simple_dir_operations;
600
601	/* directory inodes start off with i_nlink == 2 (for "." entry) */
602	inc_nlink(inode);
603	d_instantiate(dentry, inode);
604	inc_nlink(d_inode(dentry->d_parent));
605	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
606	return end_creating(dentry);
607}
608EXPORT_SYMBOL_GPL(debugfs_create_dir);
609
610/**
611 * debugfs_create_automount - create automount point in the debugfs filesystem
612 * @name: a pointer to a string containing the name of the file to create.
613 * @parent: a pointer to the parent dentry for this file.  This should be a
614 *          directory dentry if set.  If this parameter is NULL, then the
615 *          file will be created in the root of the debugfs filesystem.
616 * @f: function to be called when pathname resolution steps on that one.
617 * @data: opaque argument to pass to f().
618 *
619 * @f should return what ->d_automount() would.
620 */
621struct dentry *debugfs_create_automount(const char *name,
622					struct dentry *parent,
623					debugfs_automount_t f,
624					void *data)
625{
626	struct dentry *dentry = start_creating(name, parent);
627	struct debugfs_fsdata *fsd;
628	struct inode *inode;
629
630	if (IS_ERR(dentry))
631		return dentry;
632
633	fsd = kzalloc(sizeof(*fsd), GFP_KERNEL);
634	if (!fsd) {
635		failed_creating(dentry);
636		return ERR_PTR(-ENOMEM);
637	}
638
639	fsd->automount = f;
640
641	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
642		failed_creating(dentry);
643		kfree(fsd);
644		return ERR_PTR(-EPERM);
645	}
646
647	inode = debugfs_get_inode(dentry->d_sb);
648	if (unlikely(!inode)) {
649		pr_err("out of free dentries, can not create automount '%s'\n",
650		       name);
651		kfree(fsd);
652		return failed_creating(dentry);
653	}
654
655	make_empty_dir_inode(inode);
656	inode->i_flags |= S_AUTOMOUNT;
657	inode->i_private = data;
658	dentry->d_fsdata = fsd;
659	/* directory inodes start off with i_nlink == 2 (for "." entry) */
660	inc_nlink(inode);
661	d_instantiate(dentry, inode);
662	inc_nlink(d_inode(dentry->d_parent));
663	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
664	return end_creating(dentry);
665}
666EXPORT_SYMBOL(debugfs_create_automount);
667
668/**
669 * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
670 * @name: a pointer to a string containing the name of the symbolic link to
671 *        create.
672 * @parent: a pointer to the parent dentry for this symbolic link.  This
673 *          should be a directory dentry if set.  If this parameter is NULL,
674 *          then the symbolic link will be created in the root of the debugfs
675 *          filesystem.
676 * @target: a pointer to a string containing the path to the target of the
677 *          symbolic link.
678 *
679 * This function creates a symbolic link with the given name in debugfs that
680 * links to the given target path.
681 *
682 * This function will return a pointer to a dentry if it succeeds.  This
683 * pointer must be passed to the debugfs_remove() function when the symbolic
684 * link is to be removed (no automatic cleanup happens if your module is
685 * unloaded, you are responsible here.)  If an error occurs, ERR_PTR(-ERROR)
686 * will be returned.
687 *
688 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
689 * returned.
690 */
691struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
692				      const char *target)
693{
694	struct dentry *dentry;
695	struct inode *inode;
696	char *link = kstrdup(target, GFP_KERNEL);
697	if (!link)
698		return ERR_PTR(-ENOMEM);
699
700	dentry = start_creating(name, parent);
701	if (IS_ERR(dentry)) {
702		kfree(link);
703		return dentry;
704	}
705
706	inode = debugfs_get_inode(dentry->d_sb);
707	if (unlikely(!inode)) {
708		pr_err("out of free dentries, can not create symlink '%s'\n",
709		       name);
710		kfree(link);
711		return failed_creating(dentry);
712	}
713	inode->i_mode = S_IFLNK | S_IRWXUGO;
714	inode->i_op = &debugfs_symlink_inode_operations;
715	inode->i_link = link;
716	d_instantiate(dentry, inode);
717	return end_creating(dentry);
718}
719EXPORT_SYMBOL_GPL(debugfs_create_symlink);
720
721static void __debugfs_file_removed(struct dentry *dentry)
722{
723	struct debugfs_fsdata *fsd;
724
725	/*
726	 * Paired with the closing smp_mb() implied by a successful
727	 * cmpxchg() in debugfs_file_get(): either
728	 * debugfs_file_get() must see a dead dentry or we must see a
729	 * debugfs_fsdata instance at ->d_fsdata here (or both).
730	 */
731	smp_mb();
732	fsd = READ_ONCE(dentry->d_fsdata);
733	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
734		return;
735
736	/* if this was the last reference, we're done */
737	if (refcount_dec_and_test(&fsd->active_users))
738		return;
739
740	/*
741	 * If there's still a reference, the code that obtained it can
742	 * be in different states:
743	 *  - The common case of not using cancellations, or already
744	 *    after debugfs_leave_cancellation(), where we just need
745	 *    to wait for debugfs_file_put() which signals the completion;
746	 *  - inside a cancellation section, i.e. between
747	 *    debugfs_enter_cancellation() and debugfs_leave_cancellation(),
748	 *    in which case we need to trigger the ->cancel() function,
749	 *    and then wait for debugfs_file_put() just like in the
750	 *    previous case;
751	 *  - before debugfs_enter_cancellation() (but obviously after
752	 *    debugfs_file_get()), in which case we may not see the
753	 *    cancellation in the list on the first round of the loop,
754	 *    but debugfs_enter_cancellation() signals the completion
755	 *    after adding it, so this code gets woken up to call the
756	 *    ->cancel() function.
757	 */
758	while (refcount_read(&fsd->active_users)) {
759		struct debugfs_cancellation *c;
760
761		/*
762		 * Lock the cancellations. Note that the cancellations
763		 * structs are meant to be on the stack, so we need to
764		 * ensure we either use them here or don't touch them,
765		 * and debugfs_leave_cancellation() will wait for this
766		 * to be finished processing before exiting one. It may
767		 * of course win and remove the cancellation, but then
768		 * chances are we never even got into this bit, we only
769		 * do if the refcount isn't zero already.
770		 */
771		mutex_lock(&fsd->cancellations_mtx);
772		while ((c = list_first_entry_or_null(&fsd->cancellations,
773						     typeof(*c), list))) {
774			list_del_init(&c->list);
775			c->cancel(dentry, c->cancel_data);
776		}
777		mutex_unlock(&fsd->cancellations_mtx);
778
779		wait_for_completion(&fsd->active_users_drained);
780	}
781}
782
783static void remove_one(struct dentry *victim)
784{
785        if (d_is_reg(victim))
786		__debugfs_file_removed(victim);
787	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
788}
789
790/**
791 * debugfs_remove - recursively removes a directory
792 * @dentry: a pointer to a the dentry of the directory to be removed.  If this
793 *          parameter is NULL or an error value, nothing will be done.
794 *
795 * This function recursively removes a directory tree in debugfs that
796 * was previously created with a call to another debugfs function
797 * (like debugfs_create_file() or variants thereof.)
798 *
799 * This function is required to be called in order for the file to be
800 * removed, no automatic cleanup of files will happen when a module is
801 * removed, you are responsible here.
802 */
803void debugfs_remove(struct dentry *dentry)
804{
805	if (IS_ERR_OR_NULL(dentry))
806		return;
807
808	simple_pin_fs(&debug_fs_type, &debugfs_mount, &debugfs_mount_count);
809	simple_recursive_removal(dentry, remove_one);
810	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
811}
812EXPORT_SYMBOL_GPL(debugfs_remove);
813
814/**
815 * debugfs_lookup_and_remove - lookup a directory or file and recursively remove it
816 * @name: a pointer to a string containing the name of the item to look up.
817 * @parent: a pointer to the parent dentry of the item.
818 *
819 * This is the equlivant of doing something like
820 * debugfs_remove(debugfs_lookup(..)) but with the proper reference counting
821 * handled for the directory being looked up.
822 */
823void debugfs_lookup_and_remove(const char *name, struct dentry *parent)
824{
825	struct dentry *dentry;
826
827	dentry = debugfs_lookup(name, parent);
828	if (!dentry)
829		return;
830
831	debugfs_remove(dentry);
832	dput(dentry);
833}
834EXPORT_SYMBOL_GPL(debugfs_lookup_and_remove);
835
836/**
837 * debugfs_rename - rename a file/directory in the debugfs filesystem
838 * @old_dir: a pointer to the parent dentry for the renamed object. This
839 *          should be a directory dentry.
840 * @old_dentry: dentry of an object to be renamed.
841 * @new_dir: a pointer to the parent dentry where the object should be
842 *          moved. This should be a directory dentry.
843 * @new_name: a pointer to a string containing the target name.
844 *
845 * This function renames a file/directory in debugfs.  The target must not
846 * exist for rename to succeed.
847 *
848 * This function will return a pointer to old_dentry (which is updated to
849 * reflect renaming) if it succeeds. If an error occurs, ERR_PTR(-ERROR)
850 * will be returned.
851 *
852 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
853 * returned.
854 */
855struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
856		struct dentry *new_dir, const char *new_name)
857{
858	int error;
859	struct dentry *dentry = NULL, *trap;
860	struct name_snapshot old_name;
861
862	if (IS_ERR(old_dir))
863		return old_dir;
864	if (IS_ERR(new_dir))
865		return new_dir;
866	if (IS_ERR_OR_NULL(old_dentry))
867		return old_dentry;
868
869	trap = lock_rename(new_dir, old_dir);
870	/* Source or destination directories don't exist? */
871	if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
872		goto exit;
873	/* Source does not exist, cyclic rename, or mountpoint? */
874	if (d_really_is_negative(old_dentry) || old_dentry == trap ||
875	    d_mountpoint(old_dentry))
876		goto exit;
877	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
878	/* Lookup failed, cyclic rename or target exists? */
879	if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
880		goto exit;
881
882	take_dentry_name_snapshot(&old_name, old_dentry);
883
884	error = simple_rename(&nop_mnt_idmap, d_inode(old_dir), old_dentry,
885			      d_inode(new_dir), dentry, 0);
886	if (error) {
887		release_dentry_name_snapshot(&old_name);
888		goto exit;
889	}
890	d_move(old_dentry, dentry);
891	fsnotify_move(d_inode(old_dir), d_inode(new_dir), &old_name.name,
892		d_is_dir(old_dentry),
893		NULL, old_dentry);
894	release_dentry_name_snapshot(&old_name);
895	unlock_rename(new_dir, old_dir);
896	dput(dentry);
897	return old_dentry;
898exit:
899	if (dentry && !IS_ERR(dentry))
900		dput(dentry);
901	unlock_rename(new_dir, old_dir);
902	if (IS_ERR(dentry))
903		return dentry;
904	return ERR_PTR(-EINVAL);
905}
906EXPORT_SYMBOL_GPL(debugfs_rename);
907
908/**
909 * debugfs_initialized - Tells whether debugfs has been registered
910 */
911bool debugfs_initialized(void)
912{
913	return debugfs_registered;
914}
915EXPORT_SYMBOL_GPL(debugfs_initialized);
916
917static int __init debugfs_kernel(char *str)
918{
919	if (str) {
920		if (!strcmp(str, "on"))
921			debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
922		else if (!strcmp(str, "no-mount"))
923			debugfs_allow = DEBUGFS_ALLOW_API;
924		else if (!strcmp(str, "off"))
925			debugfs_allow = 0;
926	}
927
928	return 0;
929}
930early_param("debugfs", debugfs_kernel);
931static int __init debugfs_init(void)
932{
933	int retval;
934
935	if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
936		return -EPERM;
937
938	retval = sysfs_create_mount_point(kernel_kobj, "debug");
939	if (retval)
940		return retval;
941
942	retval = register_filesystem(&debug_fs_type);
943	if (retval)
944		sysfs_remove_mount_point(kernel_kobj, "debug");
945	else
946		debugfs_registered = true;
947
948	return retval;
949}
950core_initcall(debugfs_init);