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  
35  static struct vfsmount *debugfs_mount;
36  static int debugfs_mount_count;
37  static bool debugfs_registered;
38  static 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   */
debugfs_setattr(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * ia)45  static 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  
58  static const struct inode_operations debugfs_file_inode_operations = {
59  	.setattr	= debugfs_setattr,
60  };
61  static const struct inode_operations debugfs_dir_inode_operations = {
62  	.lookup		= simple_lookup,
63  	.setattr	= debugfs_setattr,
64  };
65  static const struct inode_operations debugfs_symlink_inode_operations = {
66  	.get_link	= simple_get_link,
67  	.setattr	= debugfs_setattr,
68  };
69  
debugfs_get_inode(struct super_block * sb)70  static 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  
80  struct debugfs_fs_info {
81  	kuid_t uid;
82  	kgid_t gid;
83  	umode_t mode;
84  	/* Opt_* bitfield. */
85  	unsigned int opts;
86  };
87  
88  enum {
89  	Opt_uid,
90  	Opt_gid,
91  	Opt_mode,
92  	Opt_source,
93  };
94  
95  static 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  
debugfs_parse_param(struct fs_context * fc,struct fs_parameter * param)103  static 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  
_debugfs_apply_options(struct super_block * sb,bool remount)148  static 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  
debugfs_apply_options(struct super_block * sb)170  static void debugfs_apply_options(struct super_block *sb)
171  {
172  	_debugfs_apply_options(sb, false);
173  }
174  
debugfs_apply_options_remount(struct super_block * sb)175  static void debugfs_apply_options_remount(struct super_block *sb)
176  {
177  	_debugfs_apply_options(sb, true);
178  }
179  
debugfs_reconfigure(struct fs_context * fc)180  static 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  
debugfs_show_options(struct seq_file * m,struct dentry * root)195  static 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  
debugfs_free_inode(struct inode * inode)211  static 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  
218  static 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  
debugfs_release_dentry(struct dentry * dentry)224  static 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) {
233  		WARN_ON(!list_empty(&fsd->cancellations));
234  		mutex_destroy(&fsd->cancellations_mtx);
235  	}
236  
237  	kfree(fsd);
238  }
239  
debugfs_automount(struct path * path)240  static 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  
247  static 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  
debugfs_fill_super(struct super_block * sb,struct fs_context * fc)253  static 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  
debugfs_get_tree(struct fs_context * fc)270  static 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  
debugfs_free_fc(struct fs_context * fc)278  static void debugfs_free_fc(struct fs_context *fc)
279  {
280  	kfree(fc->s_fs_info);
281  }
282  
283  static 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  
debugfs_init_fs_context(struct fs_context * fc)290  static 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  
305  static 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  };
312  MODULE_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   */
debugfs_lookup(const char * name,struct dentry * parent)326  struct 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  }
341  EXPORT_SYMBOL_GPL(debugfs_lookup);
342  
start_creating(const char * name,struct dentry * parent)343  static 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  
failed_creating(struct dentry * dentry)398  static 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  
end_creating(struct dentry * dentry)406  static struct dentry *end_creating(struct dentry *dentry)
407  {
408  	inode_unlock(d_inode(dentry->d_parent));
409  	return dentry;
410  }
411  
__debugfs_create_file(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * proxy_fops,const struct file_operations * real_fops)412  static 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 struct file_operations *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  
453  /**
454   * debugfs_create_file - create a file in the debugfs filesystem
455   * @name: a pointer to a string containing the name of the file to create.
456   * @mode: the permission that the file should have.
457   * @parent: a pointer to the parent dentry for this file.  This should be a
458   *          directory dentry if set.  If this parameter is NULL, then the
459   *          file will be created in the root of the debugfs filesystem.
460   * @data: a pointer to something that the caller will want to get to later
461   *        on.  The inode.i_private pointer will point to this value on
462   *        the open() call.
463   * @fops: a pointer to a struct file_operations that should be used for
464   *        this file.
465   *
466   * This is the basic "create a file" function for debugfs.  It allows for a
467   * wide range of flexibility in creating a file, or a directory (if you want
468   * to create a directory, the debugfs_create_dir() function is
469   * recommended to be used instead.)
470   *
471   * This function will return a pointer to a dentry if it succeeds.  This
472   * pointer must be passed to the debugfs_remove() function when the file is
473   * to be removed (no automatic cleanup happens if your module is unloaded,
474   * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
475   * returned.
476   *
477   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
478   * returned.
479   *
480   * NOTE: it's expected that most callers should _ignore_ the errors returned
481   * by this function. Other debugfs functions handle the fact that the "dentry"
482   * passed to them could be an error and they don't crash in that case.
483   * Drivers should generally work fine even if debugfs fails to init anyway.
484   */
debugfs_create_file(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * fops)485  struct dentry *debugfs_create_file(const char *name, umode_t mode,
486  				   struct dentry *parent, void *data,
487  				   const struct file_operations *fops)
488  {
489  
490  	return __debugfs_create_file(name, mode, parent, data,
491  				fops ? &debugfs_full_proxy_file_operations :
492  					&debugfs_noop_file_operations,
493  				fops);
494  }
495  EXPORT_SYMBOL_GPL(debugfs_create_file);
496  
497  /**
498   * debugfs_create_file_unsafe - create a file in the debugfs filesystem
499   * @name: a pointer to a string containing the name of the file to create.
500   * @mode: the permission that the file should have.
501   * @parent: a pointer to the parent dentry for this file.  This should be a
502   *          directory dentry if set.  If this parameter is NULL, then the
503   *          file will be created in the root of the debugfs filesystem.
504   * @data: a pointer to something that the caller will want to get to later
505   *        on.  The inode.i_private pointer will point to this value on
506   *        the open() call.
507   * @fops: a pointer to a struct file_operations that should be used for
508   *        this file.
509   *
510   * debugfs_create_file_unsafe() is completely analogous to
511   * debugfs_create_file(), the only difference being that the fops
512   * handed it will not get protected against file removals by the
513   * debugfs core.
514   *
515   * It is your responsibility to protect your struct file_operation
516   * methods against file removals by means of debugfs_file_get()
517   * and debugfs_file_put(). ->open() is still protected by
518   * debugfs though.
519   *
520   * Any struct file_operations defined by means of
521   * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and
522   * thus, may be used here.
523   */
debugfs_create_file_unsafe(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * fops)524  struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
525  				   struct dentry *parent, void *data,
526  				   const struct file_operations *fops)
527  {
528  
529  	return __debugfs_create_file(name, mode, parent, data,
530  				fops ? &debugfs_open_proxy_file_operations :
531  					&debugfs_noop_file_operations,
532  				fops);
533  }
534  EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
535  
536  /**
537   * debugfs_create_file_size - create a file in the debugfs filesystem
538   * @name: a pointer to a string containing the name of the file to create.
539   * @mode: the permission that the file should have.
540   * @parent: a pointer to the parent dentry for this file.  This should be a
541   *          directory dentry if set.  If this parameter is NULL, then the
542   *          file will be created in the root of the debugfs filesystem.
543   * @data: a pointer to something that the caller will want to get to later
544   *        on.  The inode.i_private pointer will point to this value on
545   *        the open() call.
546   * @fops: a pointer to a struct file_operations that should be used for
547   *        this file.
548   * @file_size: initial file size
549   *
550   * This is the basic "create a file" function for debugfs.  It allows for a
551   * wide range of flexibility in creating a file, or a directory (if you want
552   * to create a directory, the debugfs_create_dir() function is
553   * recommended to be used instead.)
554   */
debugfs_create_file_size(const char * name,umode_t mode,struct dentry * parent,void * data,const struct file_operations * fops,loff_t file_size)555  void debugfs_create_file_size(const char *name, umode_t mode,
556  			      struct dentry *parent, void *data,
557  			      const struct file_operations *fops,
558  			      loff_t file_size)
559  {
560  	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
561  
562  	if (!IS_ERR(de))
563  		d_inode(de)->i_size = file_size;
564  }
565  EXPORT_SYMBOL_GPL(debugfs_create_file_size);
566  
567  /**
568   * debugfs_create_dir - create a directory in the debugfs filesystem
569   * @name: a pointer to a string containing the name of the directory to
570   *        create.
571   * @parent: a pointer to the parent dentry for this file.  This should be a
572   *          directory dentry if set.  If this parameter is NULL, then the
573   *          directory will be created in the root of the debugfs filesystem.
574   *
575   * This function creates a directory in debugfs with the given name.
576   *
577   * This function will return a pointer to a dentry if it succeeds.  This
578   * pointer must be passed to the debugfs_remove() function when the file is
579   * to be removed (no automatic cleanup happens if your module is unloaded,
580   * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
581   * returned.
582   *
583   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
584   * returned.
585   *
586   * NOTE: it's expected that most callers should _ignore_ the errors returned
587   * by this function. Other debugfs functions handle the fact that the "dentry"
588   * passed to them could be an error and they don't crash in that case.
589   * Drivers should generally work fine even if debugfs fails to init anyway.
590   */
debugfs_create_dir(const char * name,struct dentry * parent)591  struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
592  {
593  	struct dentry *dentry = start_creating(name, parent);
594  	struct inode *inode;
595  
596  	if (IS_ERR(dentry))
597  		return dentry;
598  
599  	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
600  		failed_creating(dentry);
601  		return ERR_PTR(-EPERM);
602  	}
603  
604  	inode = debugfs_get_inode(dentry->d_sb);
605  	if (unlikely(!inode)) {
606  		pr_err("out of free dentries, can not create directory '%s'\n",
607  		       name);
608  		return failed_creating(dentry);
609  	}
610  
611  	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
612  	inode->i_op = &debugfs_dir_inode_operations;
613  	inode->i_fop = &simple_dir_operations;
614  
615  	/* directory inodes start off with i_nlink == 2 (for "." entry) */
616  	inc_nlink(inode);
617  	d_instantiate(dentry, inode);
618  	inc_nlink(d_inode(dentry->d_parent));
619  	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
620  	return end_creating(dentry);
621  }
622  EXPORT_SYMBOL_GPL(debugfs_create_dir);
623  
624  /**
625   * debugfs_create_automount - create automount point in the debugfs filesystem
626   * @name: a pointer to a string containing the name of the file to create.
627   * @parent: a pointer to the parent dentry for this file.  This should be a
628   *          directory dentry if set.  If this parameter is NULL, then the
629   *          file will be created in the root of the debugfs filesystem.
630   * @f: function to be called when pathname resolution steps on that one.
631   * @data: opaque argument to pass to f().
632   *
633   * @f should return what ->d_automount() would.
634   */
debugfs_create_automount(const char * name,struct dentry * parent,debugfs_automount_t f,void * data)635  struct dentry *debugfs_create_automount(const char *name,
636  					struct dentry *parent,
637  					debugfs_automount_t f,
638  					void *data)
639  {
640  	struct dentry *dentry = start_creating(name, parent);
641  	struct debugfs_fsdata *fsd;
642  	struct inode *inode;
643  
644  	if (IS_ERR(dentry))
645  		return dentry;
646  
647  	fsd = kzalloc(sizeof(*fsd), GFP_KERNEL);
648  	if (!fsd) {
649  		failed_creating(dentry);
650  		return ERR_PTR(-ENOMEM);
651  	}
652  
653  	fsd->automount = f;
654  
655  	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
656  		failed_creating(dentry);
657  		kfree(fsd);
658  		return ERR_PTR(-EPERM);
659  	}
660  
661  	inode = debugfs_get_inode(dentry->d_sb);
662  	if (unlikely(!inode)) {
663  		pr_err("out of free dentries, can not create automount '%s'\n",
664  		       name);
665  		kfree(fsd);
666  		return failed_creating(dentry);
667  	}
668  
669  	make_empty_dir_inode(inode);
670  	inode->i_flags |= S_AUTOMOUNT;
671  	inode->i_private = data;
672  	dentry->d_fsdata = fsd;
673  	/* directory inodes start off with i_nlink == 2 (for "." entry) */
674  	inc_nlink(inode);
675  	d_instantiate(dentry, inode);
676  	inc_nlink(d_inode(dentry->d_parent));
677  	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
678  	return end_creating(dentry);
679  }
680  EXPORT_SYMBOL(debugfs_create_automount);
681  
682  /**
683   * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
684   * @name: a pointer to a string containing the name of the symbolic link to
685   *        create.
686   * @parent: a pointer to the parent dentry for this symbolic link.  This
687   *          should be a directory dentry if set.  If this parameter is NULL,
688   *          then the symbolic link will be created in the root of the debugfs
689   *          filesystem.
690   * @target: a pointer to a string containing the path to the target of the
691   *          symbolic link.
692   *
693   * This function creates a symbolic link with the given name in debugfs that
694   * links to the given target path.
695   *
696   * This function will return a pointer to a dentry if it succeeds.  This
697   * pointer must be passed to the debugfs_remove() function when the symbolic
698   * link is to be removed (no automatic cleanup happens if your module is
699   * unloaded, you are responsible here.)  If an error occurs, ERR_PTR(-ERROR)
700   * will be returned.
701   *
702   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
703   * returned.
704   */
debugfs_create_symlink(const char * name,struct dentry * parent,const char * target)705  struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
706  				      const char *target)
707  {
708  	struct dentry *dentry;
709  	struct inode *inode;
710  	char *link = kstrdup(target, GFP_KERNEL);
711  	if (!link)
712  		return ERR_PTR(-ENOMEM);
713  
714  	dentry = start_creating(name, parent);
715  	if (IS_ERR(dentry)) {
716  		kfree(link);
717  		return dentry;
718  	}
719  
720  	inode = debugfs_get_inode(dentry->d_sb);
721  	if (unlikely(!inode)) {
722  		pr_err("out of free dentries, can not create symlink '%s'\n",
723  		       name);
724  		kfree(link);
725  		return failed_creating(dentry);
726  	}
727  	inode->i_mode = S_IFLNK | S_IRWXUGO;
728  	inode->i_op = &debugfs_symlink_inode_operations;
729  	inode->i_link = link;
730  	d_instantiate(dentry, inode);
731  	return end_creating(dentry);
732  }
733  EXPORT_SYMBOL_GPL(debugfs_create_symlink);
734  
__debugfs_file_removed(struct dentry * dentry)735  static void __debugfs_file_removed(struct dentry *dentry)
736  {
737  	struct debugfs_fsdata *fsd;
738  
739  	/*
740  	 * Paired with the closing smp_mb() implied by a successful
741  	 * cmpxchg() in debugfs_file_get(): either
742  	 * debugfs_file_get() must see a dead dentry or we must see a
743  	 * debugfs_fsdata instance at ->d_fsdata here (or both).
744  	 */
745  	smp_mb();
746  	fsd = READ_ONCE(dentry->d_fsdata);
747  	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
748  		return;
749  
750  	/* if this was the last reference, we're done */
751  	if (refcount_dec_and_test(&fsd->active_users))
752  		return;
753  
754  	/*
755  	 * If there's still a reference, the code that obtained it can
756  	 * be in different states:
757  	 *  - The common case of not using cancellations, or already
758  	 *    after debugfs_leave_cancellation(), where we just need
759  	 *    to wait for debugfs_file_put() which signals the completion;
760  	 *  - inside a cancellation section, i.e. between
761  	 *    debugfs_enter_cancellation() and debugfs_leave_cancellation(),
762  	 *    in which case we need to trigger the ->cancel() function,
763  	 *    and then wait for debugfs_file_put() just like in the
764  	 *    previous case;
765  	 *  - before debugfs_enter_cancellation() (but obviously after
766  	 *    debugfs_file_get()), in which case we may not see the
767  	 *    cancellation in the list on the first round of the loop,
768  	 *    but debugfs_enter_cancellation() signals the completion
769  	 *    after adding it, so this code gets woken up to call the
770  	 *    ->cancel() function.
771  	 */
772  	while (refcount_read(&fsd->active_users)) {
773  		struct debugfs_cancellation *c;
774  
775  		/*
776  		 * Lock the cancellations. Note that the cancellations
777  		 * structs are meant to be on the stack, so we need to
778  		 * ensure we either use them here or don't touch them,
779  		 * and debugfs_leave_cancellation() will wait for this
780  		 * to be finished processing before exiting one. It may
781  		 * of course win and remove the cancellation, but then
782  		 * chances are we never even got into this bit, we only
783  		 * do if the refcount isn't zero already.
784  		 */
785  		mutex_lock(&fsd->cancellations_mtx);
786  		while ((c = list_first_entry_or_null(&fsd->cancellations,
787  						     typeof(*c), list))) {
788  			list_del_init(&c->list);
789  			c->cancel(dentry, c->cancel_data);
790  		}
791  		mutex_unlock(&fsd->cancellations_mtx);
792  
793  		wait_for_completion(&fsd->active_users_drained);
794  	}
795  }
796  
remove_one(struct dentry * victim)797  static void remove_one(struct dentry *victim)
798  {
799          if (d_is_reg(victim))
800  		__debugfs_file_removed(victim);
801  	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
802  }
803  
804  /**
805   * debugfs_remove - recursively removes a directory
806   * @dentry: a pointer to a the dentry of the directory to be removed.  If this
807   *          parameter is NULL or an error value, nothing will be done.
808   *
809   * This function recursively removes a directory tree in debugfs that
810   * was previously created with a call to another debugfs function
811   * (like debugfs_create_file() or variants thereof.)
812   *
813   * This function is required to be called in order for the file to be
814   * removed, no automatic cleanup of files will happen when a module is
815   * removed, you are responsible here.
816   */
debugfs_remove(struct dentry * dentry)817  void debugfs_remove(struct dentry *dentry)
818  {
819  	if (IS_ERR_OR_NULL(dentry))
820  		return;
821  
822  	simple_pin_fs(&debug_fs_type, &debugfs_mount, &debugfs_mount_count);
823  	simple_recursive_removal(dentry, remove_one);
824  	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
825  }
826  EXPORT_SYMBOL_GPL(debugfs_remove);
827  
828  /**
829   * debugfs_lookup_and_remove - lookup a directory or file and recursively remove it
830   * @name: a pointer to a string containing the name of the item to look up.
831   * @parent: a pointer to the parent dentry of the item.
832   *
833   * This is the equlivant of doing something like
834   * debugfs_remove(debugfs_lookup(..)) but with the proper reference counting
835   * handled for the directory being looked up.
836   */
debugfs_lookup_and_remove(const char * name,struct dentry * parent)837  void debugfs_lookup_and_remove(const char *name, struct dentry *parent)
838  {
839  	struct dentry *dentry;
840  
841  	dentry = debugfs_lookup(name, parent);
842  	if (!dentry)
843  		return;
844  
845  	debugfs_remove(dentry);
846  	dput(dentry);
847  }
848  EXPORT_SYMBOL_GPL(debugfs_lookup_and_remove);
849  
850  /**
851   * debugfs_rename - rename a file/directory in the debugfs filesystem
852   * @old_dir: a pointer to the parent dentry for the renamed object. This
853   *          should be a directory dentry.
854   * @old_dentry: dentry of an object to be renamed.
855   * @new_dir: a pointer to the parent dentry where the object should be
856   *          moved. This should be a directory dentry.
857   * @new_name: a pointer to a string containing the target name.
858   *
859   * This function renames a file/directory in debugfs.  The target must not
860   * exist for rename to succeed.
861   *
862   * This function will return a pointer to old_dentry (which is updated to
863   * reflect renaming) if it succeeds. If an error occurs, ERR_PTR(-ERROR)
864   * will be returned.
865   *
866   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
867   * returned.
868   */
debugfs_rename(struct dentry * old_dir,struct dentry * old_dentry,struct dentry * new_dir,const char * new_name)869  struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
870  		struct dentry *new_dir, const char *new_name)
871  {
872  	int error;
873  	struct dentry *dentry = NULL, *trap;
874  	struct name_snapshot old_name;
875  
876  	if (IS_ERR(old_dir))
877  		return old_dir;
878  	if (IS_ERR(new_dir))
879  		return new_dir;
880  	if (IS_ERR_OR_NULL(old_dentry))
881  		return old_dentry;
882  
883  	trap = lock_rename(new_dir, old_dir);
884  	/* Source or destination directories don't exist? */
885  	if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
886  		goto exit;
887  	/* Source does not exist, cyclic rename, or mountpoint? */
888  	if (d_really_is_negative(old_dentry) || old_dentry == trap ||
889  	    d_mountpoint(old_dentry))
890  		goto exit;
891  	dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
892  	/* Lookup failed, cyclic rename or target exists? */
893  	if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
894  		goto exit;
895  
896  	take_dentry_name_snapshot(&old_name, old_dentry);
897  
898  	error = simple_rename(&nop_mnt_idmap, d_inode(old_dir), old_dentry,
899  			      d_inode(new_dir), dentry, 0);
900  	if (error) {
901  		release_dentry_name_snapshot(&old_name);
902  		goto exit;
903  	}
904  	d_move(old_dentry, dentry);
905  	fsnotify_move(d_inode(old_dir), d_inode(new_dir), &old_name.name,
906  		d_is_dir(old_dentry),
907  		NULL, old_dentry);
908  	release_dentry_name_snapshot(&old_name);
909  	unlock_rename(new_dir, old_dir);
910  	dput(dentry);
911  	return old_dentry;
912  exit:
913  	if (dentry && !IS_ERR(dentry))
914  		dput(dentry);
915  	unlock_rename(new_dir, old_dir);
916  	if (IS_ERR(dentry))
917  		return dentry;
918  	return ERR_PTR(-EINVAL);
919  }
920  EXPORT_SYMBOL_GPL(debugfs_rename);
921  
922  /**
923   * debugfs_initialized - Tells whether debugfs has been registered
924   */
debugfs_initialized(void)925  bool debugfs_initialized(void)
926  {
927  	return debugfs_registered;
928  }
929  EXPORT_SYMBOL_GPL(debugfs_initialized);
930  
debugfs_kernel(char * str)931  static int __init debugfs_kernel(char *str)
932  {
933  	if (str) {
934  		if (!strcmp(str, "on"))
935  			debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
936  		else if (!strcmp(str, "no-mount"))
937  			debugfs_allow = DEBUGFS_ALLOW_API;
938  		else if (!strcmp(str, "off"))
939  			debugfs_allow = 0;
940  	}
941  
942  	return 0;
943  }
944  early_param("debugfs", debugfs_kernel);
debugfs_init(void)945  static int __init debugfs_init(void)
946  {
947  	int retval;
948  
949  	if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
950  		return -EPERM;
951  
952  	retval = sysfs_create_mount_point(kernel_kobj, "debug");
953  	if (retval)
954  		return retval;
955  
956  	retval = register_filesystem(&debug_fs_type);
957  	if (retval)
958  		sysfs_remove_mount_point(kernel_kobj, "debug");
959  	else
960  		debugfs_registered = true;
961  
962  	return retval;
963  }
964  core_initcall(debugfs_init);
965