summaryrefslogtreecommitdiff
path: root/fs/tracefs/inode.c
blob: cbc8d5d2755a691a560c46f7105e85ca6220d835 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
/*
 *  inode.c - part of tracefs, a pseudo file system for activating tracing
 *
 * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
 *
 *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License version
 *	2 as published by the Free Software Foundation.
 *
 * tracefs is the file system that is used by the tracing infrastructure.
 *
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/tracefs.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>

#define TRACEFS_DEFAULT_MODE	0700

static struct vfsmount *tracefs_mount;
static int tracefs_mount_count;
static bool tracefs_registered;

static ssize_t default_read_file(struct file *file, char __user *buf,
				 size_t count, loff_t *ppos)
{
	return 0;
}

static ssize_t default_write_file(struct file *file, const char __user *buf,
				   size_t count, loff_t *ppos)
{
	return count;
}

static const struct file_operations tracefs_file_operations = {
	.read =		default_read_file,
	.write =	default_write_file,
	.open =		simple_open,
	.llseek =	noop_llseek,
};

static struct tracefs_dir_ops {
	int (*mkdir)(const char *name);
	int (*rmdir)(const char *name);
} tracefs_ops;

static char *get_dname(struct dentry *dentry)
{
	const char *dname;
	char *name;
	int len = dentry->d_name.len;

	dname = dentry->d_name.name;
	name = kmalloc(len + 1, GFP_KERNEL);
	if (!name)
		return NULL;
	memcpy(name, dname, len);
	name[len] = 0;
	return name;
}

static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
{
	char *name;
	int ret;

	name = get_dname(dentry);
	if (!name)
		return -ENOMEM;

	/*
	 * The mkdir call can call the generic functions that create
	 * the files within the tracefs system. It is up to the individual
	 * mkdir routine to handle races.
	 */
	mutex_unlock(&inode->i_mutex);
	ret = tracefs_ops.mkdir(name);
	mutex_lock(&inode->i_mutex);

	kfree(name);

	return ret;
}

static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
{
	char *name;
	int ret;

	name = get_dname(dentry);
	if (!name)
		return -ENOMEM;

	/*
	 * The rmdir call can call the generic functions that create
	 * the files within the tracefs system. It is up to the individual
	 * rmdir routine to handle races.
	 * This time we need to unlock not only the parent (inode) but
	 * also the directory that is being deleted.
	 */
	mutex_unlock(&inode->i_mutex);
	mutex_unlock(&dentry->d_inode->i_mutex);

	ret = tracefs_ops.rmdir(name);

	mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
	mutex_lock(&dentry->d_inode->i_mutex);

	kfree(name);

	return ret;
}

static const struct inode_operations tracefs_dir_inode_operations = {
	.lookup		= simple_lookup,
	.mkdir		= tracefs_syscall_mkdir,
	.rmdir		= tracefs_syscall_rmdir,
};

static struct inode *tracefs_get_inode(struct super_block *sb)
{
	struct inode *inode = new_inode(sb);
	if (inode) {
		inode->i_ino = get_next_ino();
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
	}
	return inode;
}

struct tracefs_mount_opts {
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
};

enum {
	Opt_uid,
	Opt_gid,
	Opt_mode,
	Opt_err
};

static const match_table_t tokens = {
	{Opt_uid, "uid=%u"},
	{Opt_gid, "gid=%u"},
	{Opt_mode, "mode=%o"},
	{Opt_err, NULL}
};

struct tracefs_fs_info {
	struct tracefs_mount_opts mount_opts;
};

static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
{
	substring_t args[MAX_OPT_ARGS];
	int option;
	int token;
	kuid_t uid;
	kgid_t gid;
	char *p;

	opts->mode = TRACEFS_DEFAULT_MODE;

	while ((p = strsep(&data, ",")) != NULL) {
		if (!*p)
			continue;

		token = match_token(p, tokens, args);
		switch (token) {
		case Opt_uid:
			if (match_int(&args[0], &option))
				return -EINVAL;
			uid = make_kuid(current_user_ns(), option);
			if (!uid_valid(uid))
				return -EINVAL;
			opts->uid = uid;
			break;
		case Opt_gid:
			if (match_int(&args[0], &option))
				return -EINVAL;
			gid = make_kgid(current_user_ns(), option);
			if (!gid_valid(gid))
				return -EINVAL;
			opts->gid = gid;
			break;
		case Opt_mode:
			if (match_octal(&args[0], &option))
				return -EINVAL;
			opts->mode = option & S_IALLUGO;
			break;
		/*
		 * We might like to report bad mount options here;
		 * but traditionally tracefs has ignored all mount options
		 */
		}
	}

	return 0;
}

static int tracefs_apply_options(struct super_block *sb)
{
	struct tracefs_fs_info *fsi = sb->s_fs_info;
	struct inode *inode = sb->s_root->d_inode;
	struct tracefs_mount_opts *opts = &fsi->mount_opts;

	inode->i_mode &= ~S_IALLUGO;
	inode->i_mode |= opts->mode;

	inode->i_uid = opts->uid;
	inode->i_gid = opts->gid;

	return 0;
}

static int tracefs_remount(struct super_block *sb, int *flags, char *data)
{
	int err;
	struct tracefs_fs_info *fsi = sb->s_fs_info;

	sync_filesystem(sb);
	err = tracefs_parse_options(data, &fsi->mount_opts);
	if (err)
		goto fail;

	tracefs_apply_options(sb);

fail:
	return err;
}

static int tracefs_show_options(struct seq_file *m, struct dentry *root)
{
	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
	struct tracefs_mount_opts *opts = &fsi->mount_opts;

	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
		seq_printf(m, ",uid=%u",
			   from_kuid_munged(&init_user_ns, opts->uid));
	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
		seq_printf(m, ",gid=%u",
			   from_kgid_munged(&init_user_ns, opts->gid));
	if (opts->mode != TRACEFS_DEFAULT_MODE)
		seq_printf(m, ",mode=%o", opts->mode);

	return 0;
}

static const struct super_operations tracefs_super_operations = {
	.statfs		= simple_statfs,
	.remount_fs	= tracefs_remount,
	.show_options	= tracefs_show_options,
};

static int trace_fill_super(struct super_block *sb, void *data, int silent)
{
	static struct tree_descr trace_files[] = {{""}};
	struct tracefs_fs_info *fsi;
	int err;

	save_mount_options(sb, data);

	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
	sb->s_fs_info = fsi;
	if (!fsi) {
		err = -ENOMEM;
		goto fail;
	}

	err = tracefs_parse_options(data, &fsi->mount_opts);
	if (err)
		goto fail;

	err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
	if (err)
		goto fail;

	sb->s_op = &tracefs_super_operations;

	tracefs_apply_options(sb);

	return 0;

fail:
	kfree(fsi);
	sb->s_fs_info = NULL;
	return err;
}

static struct dentry *trace_mount(struct file_system_type *fs_type,
			int flags, const char *dev_name,
			void *data)
{
	return mount_single(fs_type, flags, data, trace_fill_super);
}

static struct file_system_type trace_fs_type = {
	.owner =	THIS_MODULE,
	.name =		"tracefs",
	.mount =	trace_mount,
	.kill_sb =	kill_litter_super,
};
MODULE_ALIAS_FS("tracefs");

static struct dentry *start_creating(const char *name, struct dentry *parent)
{
	struct dentry *dentry;
	int error;

	pr_debug("tracefs: creating file '%s'\n",name);

	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
			      &tracefs_mount_count);
	if (error)
		return ERR_PTR(error);

	/* If the parent is not specified, we create it in the root.
	 * We need the root dentry to do this, which is in the super
	 * block. A pointer to that is in the struct vfsmount that we
	 * have around.
	 */
	if (!parent)
		parent = tracefs_mount->mnt_root;

	mutex_lock(&parent->d_inode->i_mutex);
	dentry = lookup_one_len(name, parent, strlen(name));
	if (!IS_ERR(dentry) && dentry->d_inode) {
		dput(dentry);
		dentry = ERR_PTR(-EEXIST);
	}
	if (IS_ERR(dentry))
		mutex_unlock(&parent->d_inode->i_mutex);
	return dentry;
}

static struct dentry *failed_creating(struct dentry *dentry)
{
	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
	dput(dentry);
	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
	return NULL;
}

static struct dentry *end_creating(struct dentry *dentry)
{
	mutex_unlock(&dentry->d_parent->d_inode->i_mutex);
	return dentry;
}

/**
 * tracefs_create_file - create a file in the tracefs filesystem
 * @name: a pointer to a string containing the name of the file to create.
 * @mode: the permission that the file should have.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is NULL, then the
 *          file will be created in the root of the tracefs filesystem.
 * @data: a pointer to something that the caller will want to get to later
 *        on.  The inode.i_private pointer will point to this value on
 *        the open() call.
 * @fops: a pointer to a struct file_operations that should be used for
 *        this file.
 *
 * This is the basic "create a file" function for tracefs.  It allows for a
 * wide range of flexibility in creating a file, or a directory (if you want
 * to create a directory, the tracefs_create_dir() function is
 * recommended to be used instead.)
 *
 * This function will return a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the tracefs_remove() function when the file is
 * to be removed (no automatic cleanup happens if your module is unloaded,
 * you are responsible here.)  If an error occurs, %NULL will be returned.
 *
 * If tracefs is not enabled in the kernel, the value -%ENODEV will be
 * returned.
 */
struct dentry *tracefs_create_file(const char *name, umode_t mode,
				   struct dentry *parent, void *data,
				   const struct file_operations *fops)
{
	struct dentry *dentry;
	struct inode *inode;

	if (!(mode & S_IFMT))
		mode |= S_IFREG;
	BUG_ON(!S_ISREG(mode));
	dentry = start_creating(name, parent);

	if (IS_ERR(dentry))
		return NULL;

	inode = tracefs_get_inode(dentry->d_sb);
	if (unlikely(!inode))
		return failed_creating(dentry);

	inode->i_mode = mode;
	inode->i_fop = fops ? fops : &tracefs_file_operations;
	inode->i_private = data;
	d_instantiate(dentry, inode);
	fsnotify_create(dentry->d_parent->d_inode, dentry);
	return end_creating(dentry);
}

static struct dentry *__create_dir(const char *name, struct dentry *parent,
				   const struct inode_operations *ops)
{
	struct dentry *dentry = start_creating(name, parent);
	struct inode *inode;

	if (IS_ERR(dentry))
		return NULL;

	inode = tracefs_get_inode(dentry->d_sb);
	if (unlikely(!inode))
		return failed_creating(dentry);

	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
	inode->i_op = ops;
	inode->i_fop = &simple_dir_operations;

	/* directory inodes start off with i_nlink == 2 (for "." entry) */
	inc_nlink(inode);
	d_instantiate(dentry, inode);
	inc_nlink(dentry->d_parent->d_inode);
	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
	return end_creating(dentry);
}

/**
 * tracefs_create_dir - create a directory in the tracefs filesystem
 * @name: a pointer to a string containing the name of the directory to
 *        create.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is NULL, then the
 *          directory will be created in the root of the tracefs filesystem.
 *
 * This function creates a directory in tracefs with the given name.
 *
 * This function will return a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the tracefs_remove() function when the file is
 * to be removed. If an error occurs, %NULL will be returned.
 *
 * If tracing is not enabled in the kernel, the value -%ENODEV will be
 * returned.
 */
struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
{
	return __create_dir(name, parent, &simple_dir_inode_operations);
}

/**
 * tracefs_create_instance_dir - create the tracing instances directory
 * @name: The name of the instances directory to create
 * @parent: The parent directory that the instances directory will exist
 * @mkdir: The function to call when a mkdir is performed.
 * @rmdir: The function to call when a rmdir is performed.
 *
 * Only one instances directory is allowed.
 *
 * The instances directory is special as it allows for mkdir and rmdir to
 * to be done by userspace. When a mkdir or rmdir is performed, the inode
 * locks are released and the methhods passed in (@mkdir and @rmdir) are
 * called without locks and with the name of the directory being created
 * within the instances directory.
 *
 * Returns the dentry of the instances directory.
 */
struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
					  int (*mkdir)(const char *name),
					  int (*rmdir)(const char *name))
{
	struct dentry *dentry;

	/* Only allow one instance of the instances directory. */
	if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
		return NULL;

	dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
	if (!dentry)
		return NULL;

	tracefs_ops.mkdir = mkdir;
	tracefs_ops.rmdir = rmdir;

	return dentry;
}

static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
{
	int ret = 0;

	if (simple_positive(dentry)) {
		if (dentry->d_inode) {
			dget(dentry);
			switch (dentry->d_inode->i_mode & S_IFMT) {
			case S_IFDIR:
				ret = simple_rmdir(parent->d_inode, dentry);
				break;
			default:
				simple_unlink(parent->d_inode, dentry);
				break;
			}
			if (!ret)
				d_delete(dentry);
			dput(dentry);
		}
	}
	return ret;
}

/**
 * tracefs_remove - removes a file or directory from the tracefs filesystem
 * @dentry: a pointer to a the dentry of the file or directory to be
 *          removed.
 *
 * This function removes a file or directory in tracefs that was previously
 * created with a call to another tracefs function (like
 * tracefs_create_file() or variants thereof.)
 */
void tracefs_remove(struct dentry *dentry)
{
	struct dentry *parent;
	int ret;

	if (IS_ERR_OR_NULL(dentry))
		return;

	parent = dentry->d_parent;
	if (!parent || !parent->d_inode)
		return;

	mutex_lock(&parent->d_inode->i_mutex);
	ret = __tracefs_remove(dentry, parent);
	mutex_unlock(&parent->d_inode->i_mutex);
	if (!ret)
		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
}

/**
 * tracefs_remove_recursive - recursively removes a directory
 * @dentry: a pointer to a the dentry of the directory to be removed.
 *
 * This function recursively removes a directory tree in tracefs that
 * was previously created with a call to another tracefs function
 * (like tracefs_create_file() or variants thereof.)
 */
void tracefs_remove_recursive(struct dentry *dentry)
{
	struct dentry *child, *parent;

	if (IS_ERR_OR_NULL(dentry))
		return;

	parent = dentry->d_parent;
	if (!parent || !parent->d_inode)
		return;

	parent = dentry;
 down:
	mutex_lock(&parent->d_inode->i_mutex);
 loop:
	/*
	 * The parent->d_subdirs is protected by the d_lock. Outside that
	 * lock, the child can be unlinked and set to be freed which can
	 * use the d_u.d_child as the rcu head and corrupt this list.
	 */
	spin_lock(&parent->d_lock);
	list_for_each_entry(child, &parent->d_subdirs, d_child) {
		if (!simple_positive(child))
			continue;

		/* perhaps simple_empty(child) makes more sense */
		if (!list_empty(&child->d_subdirs)) {
			spin_unlock(&parent->d_lock);
			mutex_unlock(&parent->d_inode->i_mutex);
			parent = child;
			goto down;
		}

		spin_unlock(&parent->d_lock);

		if (!__tracefs_remove(child, parent))
			simple_release_fs(&tracefs_mount, &tracefs_mount_count);

		/*
		 * The parent->d_lock protects agaist child from unlinking
		 * from d_subdirs. When releasing the parent->d_lock we can
		 * no longer trust that the next pointer is valid.
		 * Restart the loop. We'll skip this one with the
		 * simple_positive() check.
		 */
		goto loop;
	}
	spin_unlock(&parent->d_lock);

	mutex_unlock(&parent->d_inode->i_mutex);
	child = parent;
	parent = parent->d_parent;
	mutex_lock(&parent->d_inode->i_mutex);

	if (child != dentry)
		/* go up */
		goto loop;

	if (!__tracefs_remove(child, parent))
		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
	mutex_unlock(&parent->d_inode->i_mutex);
}

/**
 * tracefs_initialized - Tells whether tracefs has been registered
 */
bool tracefs_initialized(void)
{
	return tracefs_registered;
}

static int __init tracefs_init(void)
{
	int retval;

	retval = sysfs_create_mount_point(kernel_kobj, "tracing");
	if (retval)
		return -EINVAL;

	retval = register_filesystem(&trace_fs_type);
	if (!retval)
		tracefs_registered = true;

	return retval;
}
core_initcall(tracefs_init);