summaryrefslogtreecommitdiff
path: root/drivers/staging/android/logger.c
blob: b040200a5a5502d7a110e9064d25b10600196065 (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
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
/*
 * drivers/misc/logger.c
 *
 * A Logging Subsystem
 *
 * Copyright (C) 2007-2008 Google, Inc.
 *
 * Robert Love <rlove@google.com>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#define pr_fmt(fmt) "logger: " fmt

#include <linux/sched.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/vmalloc.h>
#include <linux/aio.h>
#include "logger.h"

#include <asm/ioctls.h>

/**
 * struct logger_log - represents a specific log, such as 'main' or 'radio'
 * @buffer:	The actual ring buffer
 * @misc:	The "misc" device representing the log
 * @wq:		The wait queue for @readers
 * @readers:	This log's readers
 * @mutex:	The mutex that protects the @buffer
 * @w_off:	The current write head offset
 * @head:	The head, or location that readers start reading at.
 * @size:	The size of the log
 * @logs:	The list of log channels
 *
 * This structure lives from module insertion until module removal, so it does
 * not need additional reference counting. The structure is protected by the
 * mutex 'mutex'.
 */
struct logger_log {
	unsigned char		*buffer;
	struct miscdevice	misc;
	wait_queue_head_t	wq;
	struct list_head	readers;
	struct mutex		mutex;
	size_t			w_off;
	size_t			head;
	size_t			size;
	struct list_head	logs;
};

static LIST_HEAD(log_list);


/**
 * struct logger_reader - a logging device open for reading
 * @log:	The associated log
 * @list:	The associated entry in @logger_log's list
 * @r_off:	The current read head offset.
 * @r_all:	Reader can read all entries
 * @r_ver:	Reader ABI version
 *
 * This object lives from open to release, so we don't need additional
 * reference counting. The structure is protected by log->mutex.
 */
struct logger_reader {
	struct logger_log	*log;
	struct list_head	list;
	size_t			r_off;
	bool			r_all;
	int			r_ver;
};

/* logger_offset - returns index 'n' into the log via (optimized) modulus */
static size_t logger_offset(struct logger_log *log, size_t n)
{
	return n & (log->size - 1);
}


/*
 * file_get_log - Given a file structure, return the associated log
 *
 * This isn't aesthetic. We have several goals:
 *
 *	1) Need to quickly obtain the associated log during an I/O operation
 *	2) Readers need to maintain state (logger_reader)
 *	3) Writers need to be very fast (open() should be a near no-op)
 *
 * In the reader case, we can trivially go file->logger_reader->logger_log.
 * For a writer, we don't want to maintain a logger_reader, so we just go
 * file->logger_log. Thus what file->private_data points at depends on whether
 * or not the file was opened for reading. This function hides that dirtiness.
 */
static inline struct logger_log *file_get_log(struct file *file)
{
	if (file->f_mode & FMODE_READ) {
		struct logger_reader *reader = file->private_data;
		return reader->log;
	} else
		return file->private_data;
}

/*
 * get_entry_header - returns a pointer to the logger_entry header within
 * 'log' starting at offset 'off'. A temporary logger_entry 'scratch' must
 * be provided. Typically the return value will be a pointer within
 * 'logger->buf'.  However, a pointer to 'scratch' may be returned if
 * the log entry spans the end and beginning of the circular buffer.
 */
static struct logger_entry *get_entry_header(struct logger_log *log,
		size_t off, struct logger_entry *scratch)
{
	size_t len = min(sizeof(struct logger_entry), log->size - off);
	if (len != sizeof(struct logger_entry)) {
		memcpy(((void *) scratch), log->buffer + off, len);
		memcpy(((void *) scratch) + len, log->buffer,
			sizeof(struct logger_entry) - len);
		return scratch;
	}

	return (struct logger_entry *) (log->buffer + off);
}

/*
 * get_entry_msg_len - Grabs the length of the message of the entry
 * starting from from 'off'.
 *
 * An entry length is 2 bytes (16 bits) in host endian order.
 * In the log, the length does not include the size of the log entry structure.
 * This function returns the size including the log entry structure.
 *
 * Caller needs to hold log->mutex.
 */
static __u32 get_entry_msg_len(struct logger_log *log, size_t off)
{
	struct logger_entry scratch;
	struct logger_entry *entry;

	entry = get_entry_header(log, off, &scratch);
	return entry->len;
}

static size_t get_user_hdr_len(int ver)
{
	if (ver < 2)
		return sizeof(struct user_logger_entry_compat);
	else
		return sizeof(struct logger_entry);
}

static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
					 char __user *buf)
{
	void *hdr;
	size_t hdr_len;
	struct user_logger_entry_compat v1;

	if (ver < 2) {
		v1.len      = entry->len;
		v1.__pad    = 0;
		v1.pid      = entry->pid;
		v1.tid      = entry->tid;
		v1.sec      = entry->sec;
		v1.nsec     = entry->nsec;
		hdr         = &v1;
		hdr_len     = sizeof(struct user_logger_entry_compat);
	} else {
		hdr         = entry;
		hdr_len     = sizeof(struct logger_entry);
	}

	return copy_to_user(buf, hdr, hdr_len);
}

/*
 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
 * user-space buffer 'buf'. Returns 'count' on success.
 *
 * Caller must hold log->mutex.
 */
static ssize_t do_read_log_to_user(struct logger_log *log,
				   struct logger_reader *reader,
				   char __user *buf,
				   size_t count)
{
	struct logger_entry scratch;
	struct logger_entry *entry;
	size_t len;
	size_t msg_start;

	/*
	 * First, copy the header to userspace, using the version of
	 * the header requested
	 */
	entry = get_entry_header(log, reader->r_off, &scratch);
	if (copy_header_to_user(reader->r_ver, entry, buf))
		return -EFAULT;

	count -= get_user_hdr_len(reader->r_ver);
	buf += get_user_hdr_len(reader->r_ver);
	msg_start = logger_offset(log,
		reader->r_off + sizeof(struct logger_entry));

	/*
	 * We read from the msg in two disjoint operations. First, we read from
	 * the current msg head offset up to 'count' bytes or to the end of
	 * the log, whichever comes first.
	 */
	len = min(count, log->size - msg_start);
	if (copy_to_user(buf, log->buffer + msg_start, len))
		return -EFAULT;

	/*
	 * Second, we read any remaining bytes, starting back at the head of
	 * the log.
	 */
	if (count != len)
		if (copy_to_user(buf + len, log->buffer, count - len))
			return -EFAULT;

	reader->r_off = logger_offset(log, reader->r_off +
		sizeof(struct logger_entry) + count);

	return count + get_user_hdr_len(reader->r_ver);
}

/*
 * get_next_entry_by_uid - Starting at 'off', returns an offset into
 * 'log->buffer' which contains the first entry readable by 'euid'
 */
static size_t get_next_entry_by_uid(struct logger_log *log,
		size_t off, uid_t euid)
{
	while (off != log->w_off) {
		struct logger_entry *entry;
		struct logger_entry scratch;
		size_t next_len;

		entry = get_entry_header(log, off, &scratch);

		if (entry->euid == euid)
			return off;

		next_len = sizeof(struct logger_entry) + entry->len;
		off = logger_offset(log, off + next_len);
	}

	return off;
}

/*
 * logger_read - our log's read() method
 *
 * Behavior:
 *
 *	- O_NONBLOCK works
 *	- If there are no log entries to read, blocks until log is written to
 *	- Atomically reads exactly one log entry
 *
 * Will set errno to EINVAL if read
 * buffer is insufficient to hold next entry.
 */
static ssize_t logger_read(struct file *file, char __user *buf,
			   size_t count, loff_t *pos)
{
	struct logger_reader *reader = file->private_data;
	struct logger_log *log = reader->log;
	ssize_t ret;
	DEFINE_WAIT(wait);

start:
	while (1) {
		mutex_lock(&log->mutex);

		prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);

		ret = (log->w_off == reader->r_off);
		mutex_unlock(&log->mutex);
		if (!ret)
			break;

		if (file->f_flags & O_NONBLOCK) {
			ret = -EAGAIN;
			break;
		}

		if (signal_pending(current)) {
			ret = -EINTR;
			break;
		}

		schedule();
	}

	finish_wait(&log->wq, &wait);
	if (ret)
		return ret;

	mutex_lock(&log->mutex);

	if (!reader->r_all)
		reader->r_off = get_next_entry_by_uid(log,
			reader->r_off, current_euid());

	/* is there still something to read or did we race? */
	if (unlikely(log->w_off == reader->r_off)) {
		mutex_unlock(&log->mutex);
		goto start;
	}

	/* get the size of the next entry */
	ret = get_user_hdr_len(reader->r_ver) +
		get_entry_msg_len(log, reader->r_off);
	if (count < ret) {
		ret = -EINVAL;
		goto out;
	}

	/* get exactly one entry from the log */
	ret = do_read_log_to_user(log, reader, buf, ret);

out:
	mutex_unlock(&log->mutex);

	return ret;
}

/*
 * get_next_entry - return the offset of the first valid entry at least 'len'
 * bytes after 'off'.
 *
 * Caller must hold log->mutex.
 */
static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
{
	size_t count = 0;

	do {
		size_t nr = sizeof(struct logger_entry) +
			get_entry_msg_len(log, off);
		off = logger_offset(log, off + nr);
		count += nr;
	} while (count < len);

	return off;
}

/*
 * is_between - is a < c < b, accounting for wrapping of a, b, and c
 *    positions in the buffer
 *
 * That is, if a<b, check for c between a and b
 * and if a>b, check for c outside (not between) a and b
 *
 * |------- a xxxxxxxx b --------|
 *               c^
 *
 * |xxxxx b --------- a xxxxxxxxx|
 *    c^
 *  or                    c^
 */
static inline int is_between(size_t a, size_t b, size_t c)
{
	if (a < b) {
		/* is c between a and b? */
		if (a < c && c <= b)
			return 1;
	} else {
		/* is c outside of b through a? */
		if (c <= b || a < c)
			return 1;
	}

	return 0;
}

/*
 * fix_up_readers - walk the list of all readers and "fix up" any who were
 * lapped by the writer; also do the same for the default "start head".
 * We do this by "pulling forward" the readers and start head to the first
 * entry after the new write head.
 *
 * The caller needs to hold log->mutex.
 */
static void fix_up_readers(struct logger_log *log, size_t len)
{
	size_t old = log->w_off;
	size_t new = logger_offset(log, old + len);
	struct logger_reader *reader;

	if (is_between(old, new, log->head))
		log->head = get_next_entry(log, log->head, len);

	list_for_each_entry(reader, &log->readers, list)
		if (is_between(old, new, reader->r_off))
			reader->r_off = get_next_entry(log, reader->r_off, len);
}

/*
 * do_write_log - writes 'len' bytes from 'buf' to 'log'
 *
 * The caller needs to hold log->mutex.
 */
static void do_write_log(struct logger_log *log, const void *buf, size_t count)
{
	size_t len;

	len = min(count, log->size - log->w_off);
	memcpy(log->buffer + log->w_off, buf, len);

	if (count != len)
		memcpy(log->buffer, buf + len, count - len);

	log->w_off = logger_offset(log, log->w_off + count);

}

/*
 * do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
 * the log 'log'
 *
 * The caller needs to hold log->mutex.
 *
 * Returns 'count' on success, negative error code on failure.
 */
static ssize_t do_write_log_from_user(struct logger_log *log,
				      const void __user *buf, size_t count)
{
	size_t len;

	len = min(count, log->size - log->w_off);
	if (len && copy_from_user(log->buffer + log->w_off, buf, len))
		return -EFAULT;

	if (count != len)
		if (copy_from_user(log->buffer, buf + len, count - len))
			/*
			 * Note that by not updating w_off, this abandons the
			 * portion of the new entry that *was* successfully
			 * copied, just above.  This is intentional to avoid
			 * message corruption from missing fragments.
			 */
			return -EFAULT;

	log->w_off = logger_offset(log, log->w_off + count);

	return count;
}

/*
 * logger_aio_write - our write method, implementing support for write(),
 * writev(), and aio_write(). Writes are our fast path, and we try to optimize
 * them above all else.
 */
static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
			 unsigned long nr_segs, loff_t ppos)
{
	struct logger_log *log = file_get_log(iocb->ki_filp);
	size_t orig = log->w_off;
	struct logger_entry header;
	struct timespec now;
	ssize_t ret = 0;

	now = current_kernel_time();

	header.pid = current->tgid;
	header.tid = current->pid;
	header.sec = now.tv_sec;
	header.nsec = now.tv_nsec;
	header.euid = current_euid();
	header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
	header.hdr_size = sizeof(struct logger_entry);

	/* null writes succeed, return zero */
	if (unlikely(!header.len))
		return 0;

	mutex_lock(&log->mutex);

	/*
	 * Fix up any readers, pulling them forward to the first readable
	 * entry after (what will be) the new write offset. We do this now
	 * because if we partially fail, we can end up with clobbered log
	 * entries that encroach on readable buffer.
	 */
	fix_up_readers(log, sizeof(struct logger_entry) + header.len);

	do_write_log(log, &header, sizeof(struct logger_entry));

	while (nr_segs-- > 0) {
		size_t len;
		ssize_t nr;

		/* figure out how much of this vector we can keep */
		len = min_t(size_t, iov->iov_len, header.len - ret);

		/* write out this segment's payload */
		nr = do_write_log_from_user(log, iov->iov_base, len);
		if (unlikely(nr < 0)) {
			log->w_off = orig;
			mutex_unlock(&log->mutex);
			return nr;
		}

		iov++;
		ret += nr;
	}

	mutex_unlock(&log->mutex);

	/* wake up any blocked readers */
	wake_up_interruptible(&log->wq);

	return ret;
}

static struct logger_log *get_log_from_minor(int minor)
{
	struct logger_log *log;

	list_for_each_entry(log, &log_list, logs)
		if (log->misc.minor == minor)
			return log;
	return NULL;
}

/*
 * logger_open - the log's open() file operation
 *
 * Note how near a no-op this is in the write-only case. Keep it that way!
 */
static int logger_open(struct inode *inode, struct file *file)
{
	struct logger_log *log;
	int ret;

	ret = nonseekable_open(inode, file);
	if (ret)
		return ret;

	log = get_log_from_minor(MINOR(inode->i_rdev));
	if (!log)
		return -ENODEV;

	if (file->f_mode & FMODE_READ) {
		struct logger_reader *reader;

		reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
		if (!reader)
			return -ENOMEM;

		reader->log = log;
		reader->r_ver = 1;
		reader->r_all = in_egroup_p(inode->i_gid) ||
			capable(CAP_SYSLOG);

		INIT_LIST_HEAD(&reader->list);

		mutex_lock(&log->mutex);
		reader->r_off = log->head;
		list_add_tail(&reader->list, &log->readers);
		mutex_unlock(&log->mutex);

		file->private_data = reader;
	} else
		file->private_data = log;

	return 0;
}

/*
 * logger_release - the log's release file operation
 *
 * Note this is a total no-op in the write-only case. Keep it that way!
 */
static int logger_release(struct inode *ignored, struct file *file)
{
	if (file->f_mode & FMODE_READ) {
		struct logger_reader *reader = file->private_data;
		struct logger_log *log = reader->log;

		mutex_lock(&log->mutex);
		list_del(&reader->list);
		mutex_unlock(&log->mutex);

		kfree(reader);
	}

	return 0;
}

/*
 * logger_poll - the log's poll file operation, for poll/select/epoll
 *
 * Note we always return POLLOUT, because you can always write() to the log.
 * Note also that, strictly speaking, a return value of POLLIN does not
 * guarantee that the log is readable without blocking, as there is a small
 * chance that the writer can lap the reader in the interim between poll()
 * returning and the read() request.
 */
static unsigned int logger_poll(struct file *file, poll_table *wait)
{
	struct logger_reader *reader;
	struct logger_log *log;
	unsigned int ret = POLLOUT | POLLWRNORM;

	if (!(file->f_mode & FMODE_READ))
		return ret;

	reader = file->private_data;
	log = reader->log;

	poll_wait(file, &log->wq, wait);

	mutex_lock(&log->mutex);
	if (!reader->r_all)
		reader->r_off = get_next_entry_by_uid(log,
			reader->r_off, current_euid());

	if (log->w_off != reader->r_off)
		ret |= POLLIN | POLLRDNORM;
	mutex_unlock(&log->mutex);

	return ret;
}

static long logger_set_version(struct logger_reader *reader, void __user *arg)
{
	int version;
	if (copy_from_user(&version, arg, sizeof(int)))
		return -EFAULT;

	if ((version < 1) || (version > 2))
		return -EINVAL;

	reader->r_ver = version;
	return 0;
}

static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct logger_log *log = file_get_log(file);
	struct logger_reader *reader;
	long ret = -EINVAL;
	void __user *argp = (void __user *) arg;

	mutex_lock(&log->mutex);

	switch (cmd) {
	case LOGGER_GET_LOG_BUF_SIZE:
		ret = log->size;
		break;
	case LOGGER_GET_LOG_LEN:
		if (!(file->f_mode & FMODE_READ)) {
			ret = -EBADF;
			break;
		}
		reader = file->private_data;
		if (log->w_off >= reader->r_off)
			ret = log->w_off - reader->r_off;
		else
			ret = (log->size - reader->r_off) + log->w_off;
		break;
	case LOGGER_GET_NEXT_ENTRY_LEN:
		if (!(file->f_mode & FMODE_READ)) {
			ret = -EBADF;
			break;
		}
		reader = file->private_data;

		if (!reader->r_all)
			reader->r_off = get_next_entry_by_uid(log,
				reader->r_off, current_euid());

		if (log->w_off != reader->r_off)
			ret = get_user_hdr_len(reader->r_ver) +
				get_entry_msg_len(log, reader->r_off);
		else
			ret = 0;
		break;
	case LOGGER_FLUSH_LOG:
		if (!(file->f_mode & FMODE_WRITE)) {
			ret = -EBADF;
			break;
		}
		if (!(in_egroup_p(file->f_dentry->d_inode->i_gid) ||
				capable(CAP_SYSLOG))) {
			ret = -EPERM;
			break;
		}
		list_for_each_entry(reader, &log->readers, list)
			reader->r_off = log->w_off;
		log->head = log->w_off;
		ret = 0;
		break;
	case LOGGER_GET_VERSION:
		if (!(file->f_mode & FMODE_READ)) {
			ret = -EBADF;
			break;
		}
		reader = file->private_data;
		ret = reader->r_ver;
		break;
	case LOGGER_SET_VERSION:
		if (!(file->f_mode & FMODE_READ)) {
			ret = -EBADF;
			break;
		}
		reader = file->private_data;
		ret = logger_set_version(reader, argp);
		break;
	}

	mutex_unlock(&log->mutex);

	return ret;
}

static const struct file_operations logger_fops = {
	.owner = THIS_MODULE,
	.read = logger_read,
	.aio_write = logger_aio_write,
	.poll = logger_poll,
	.unlocked_ioctl = logger_ioctl,
	.compat_ioctl = logger_ioctl,
	.open = logger_open,
	.release = logger_release,
};

/*
 * Log size must must be a power of two, and greater than
 * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
 */
static int __init create_log(char *log_name, int size)
{
	int ret = 0;
	struct logger_log *log;
	unsigned char *buffer;

	buffer = vmalloc(size);
	if (buffer == NULL)
		return -ENOMEM;

	log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
	if (log == NULL) {
		ret = -ENOMEM;
		goto out_free_buffer;
	}
	log->buffer = buffer;

	log->misc.minor = MISC_DYNAMIC_MINOR;
	log->misc.name = kstrdup(log_name, GFP_KERNEL);
	if (log->misc.name == NULL) {
		ret = -ENOMEM;
		goto out_free_log;
	}

	log->misc.fops = &logger_fops;
	log->misc.parent = NULL;

	init_waitqueue_head(&log->wq);
	INIT_LIST_HEAD(&log->readers);
	mutex_init(&log->mutex);
	log->w_off = 0;
	log->head = 0;
	log->size = size;

	INIT_LIST_HEAD(&log->logs);
	list_add_tail(&log->logs, &log_list);

	/* finally, initialize the misc device for this log */
	ret = misc_register(&log->misc);
	if (unlikely(ret)) {
		pr_err("failed to register misc device for log '%s'!\n",
				log->misc.name);
		goto out_free_log;
	}

	pr_info("created %luK log '%s'\n",
		(unsigned long) log->size >> 10, log->misc.name);

	return 0;

out_free_log:
	kfree(log);

out_free_buffer:
	vfree(buffer);
	return ret;
}

static int __init logger_init(void)
{
	int ret;

	ret = create_log(LOGGER_LOG_MAIN, 256*1024);
	if (unlikely(ret))
		goto out;

	ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
	if (unlikely(ret))
		goto out;

	ret = create_log(LOGGER_LOG_RADIO, 256*1024);
	if (unlikely(ret))
		goto out;

	ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
	if (unlikely(ret))
		goto out;

out:
	return ret;
}

static void __exit logger_exit(void)
{
	struct logger_log *current_log, *next_log;

	list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
		/* we have to delete all the entry inside log_list */
		misc_deregister(&current_log->misc);
		vfree(current_log->buffer);
		kfree(current_log->misc.name);
		list_del(&current_log->logs);
		kfree(current_log);
	}
}


device_initcall(logger_init);
module_exit(logger_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robert Love, <rlove@google.com>");
MODULE_DESCRIPTION("Android Logger");