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/drivers/staging/android/logger.c

https://bitbucket.org/wisechild/galaxy-nexus
C | 616 lines | 368 code | 96 blank | 152 comment | 62 complexity | 3d7863840a40448f24c395da531c9aa5 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
  1/*
  2 * drivers/misc/logger.c
  3 *
  4 * A Logging Subsystem
  5 *
  6 * Copyright (C) 2007-2008 Google, Inc.
  7 *
  8 * Robert Love <rlove@google.com>
  9 *
 10 * This software is licensed under the terms of the GNU General Public
 11 * License version 2, as published by the Free Software Foundation, and
 12 * may be copied, distributed, and modified under those terms.
 13 *
 14 * This program is distributed in the hope that it will be useful,
 15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 17 * GNU General Public License for more details.
 18 */
 19
 20#include <linux/sched.h>
 21#include <linux/module.h>
 22#include <linux/fs.h>
 23#include <linux/miscdevice.h>
 24#include <linux/uaccess.h>
 25#include <linux/poll.h>
 26#include <linux/slab.h>
 27#include <linux/time.h>
 28#include "logger.h"
 29
 30#include <asm/ioctls.h>
 31
 32/*
 33 * struct logger_log - represents a specific log, such as 'main' or 'radio'
 34 *
 35 * This structure lives from module insertion until module removal, so it does
 36 * not need additional reference counting. The structure is protected by the
 37 * mutex 'mutex'.
 38 */
 39struct logger_log {
 40	unsigned char 		*buffer;/* the ring buffer itself */
 41	struct miscdevice	misc;	/* misc device representing the log */
 42	wait_queue_head_t	wq;	/* wait queue for readers */
 43	struct list_head	readers; /* this log's readers */
 44	struct mutex		mutex;	/* mutex protecting buffer */
 45	size_t			w_off;	/* current write head offset */
 46	size_t			head;	/* new readers start here */
 47	size_t			size;	/* size of the log */
 48};
 49
 50/*
 51 * struct logger_reader - a logging device open for reading
 52 *
 53 * This object lives from open to release, so we don't need additional
 54 * reference counting. The structure is protected by log->mutex.
 55 */
 56struct logger_reader {
 57	struct logger_log	*log;	/* associated log */
 58	struct list_head	list;	/* entry in logger_log's list */
 59	size_t			r_off;	/* current read head offset */
 60};
 61
 62/* logger_offset - returns index 'n' into the log via (optimized) modulus */
 63#define logger_offset(n)	((n) & (log->size - 1))
 64
 65/*
 66 * file_get_log - Given a file structure, return the associated log
 67 *
 68 * This isn't aesthetic. We have several goals:
 69 *
 70 * 	1) Need to quickly obtain the associated log during an I/O operation
 71 * 	2) Readers need to maintain state (logger_reader)
 72 * 	3) Writers need to be very fast (open() should be a near no-op)
 73 *
 74 * In the reader case, we can trivially go file->logger_reader->logger_log.
 75 * For a writer, we don't want to maintain a logger_reader, so we just go
 76 * file->logger_log. Thus what file->private_data points at depends on whether
 77 * or not the file was opened for reading. This function hides that dirtiness.
 78 */
 79static inline struct logger_log *file_get_log(struct file *file)
 80{
 81	if (file->f_mode & FMODE_READ) {
 82		struct logger_reader *reader = file->private_data;
 83		return reader->log;
 84	} else
 85		return file->private_data;
 86}
 87
 88/*
 89 * get_entry_len - Grabs the length of the payload of the next entry starting
 90 * from 'off'.
 91 *
 92 * Caller needs to hold log->mutex.
 93 */
 94static __u32 get_entry_len(struct logger_log *log, size_t off)
 95{
 96	__u16 val;
 97
 98	switch (log->size - off) {
 99	case 1:
100		memcpy(&val, log->buffer + off, 1);
101		memcpy(((char *) &val) + 1, log->buffer, 1);
102		break;
103	default:
104		memcpy(&val, log->buffer + off, 2);
105	}
106
107	return sizeof(struct logger_entry) + val;
108}
109
110/*
111 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
112 * user-space buffer 'buf'. Returns 'count' on success.
113 *
114 * Caller must hold log->mutex.
115 */
116static ssize_t do_read_log_to_user(struct logger_log *log,
117				   struct logger_reader *reader,
118				   char __user *buf,
119				   size_t count)
120{
121	size_t len;
122
123	/*
124	 * We read from the log in two disjoint operations. First, we read from
125	 * the current read head offset up to 'count' bytes or to the end of
126	 * the log, whichever comes first.
127	 */
128	len = min(count, log->size - reader->r_off);
129	if (copy_to_user(buf, log->buffer + reader->r_off, len))
130		return -EFAULT;
131
132	/*
133	 * Second, we read any remaining bytes, starting back at the head of
134	 * the log.
135	 */
136	if (count != len)
137		if (copy_to_user(buf + len, log->buffer, count - len))
138			return -EFAULT;
139
140	reader->r_off = logger_offset(reader->r_off + count);
141
142	return count;
143}
144
145/*
146 * logger_read - our log's read() method
147 *
148 * Behavior:
149 *
150 * 	- O_NONBLOCK works
151 * 	- If there are no log entries to read, blocks until log is written to
152 * 	- Atomically reads exactly one log entry
153 *
154 * Optimal read size is LOGGER_ENTRY_MAX_LEN. Will set errno to EINVAL if read
155 * buffer is insufficient to hold next entry.
156 */
157static ssize_t logger_read(struct file *file, char __user *buf,
158			   size_t count, loff_t *pos)
159{
160	struct logger_reader *reader = file->private_data;
161	struct logger_log *log = reader->log;
162	ssize_t ret;
163	DEFINE_WAIT(wait);
164
165start:
166	while (1) {
167		prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
168
169		mutex_lock(&log->mutex);
170		ret = (log->w_off == reader->r_off);
171		mutex_unlock(&log->mutex);
172		if (!ret)
173			break;
174
175		if (file->f_flags & O_NONBLOCK) {
176			ret = -EAGAIN;
177			break;
178		}
179
180		if (signal_pending(current)) {
181			ret = -EINTR;
182			break;
183		}
184
185		schedule();
186	}
187
188	finish_wait(&log->wq, &wait);
189	if (ret)
190		return ret;
191
192	mutex_lock(&log->mutex);
193
194	/* is there still something to read or did we race? */
195	if (unlikely(log->w_off == reader->r_off)) {
196		mutex_unlock(&log->mutex);
197		goto start;
198	}
199
200	/* get the size of the next entry */
201	ret = get_entry_len(log, reader->r_off);
202	if (count < ret) {
203		ret = -EINVAL;
204		goto out;
205	}
206
207	/* get exactly one entry from the log */
208	ret = do_read_log_to_user(log, reader, buf, ret);
209
210out:
211	mutex_unlock(&log->mutex);
212
213	return ret;
214}
215
216/*
217 * get_next_entry - return the offset of the first valid entry at least 'len'
218 * bytes after 'off'.
219 *
220 * Caller must hold log->mutex.
221 */
222static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
223{
224	size_t count = 0;
225
226	do {
227		size_t nr = get_entry_len(log, off);
228		off = logger_offset(off + nr);
229		count += nr;
230	} while (count < len);
231
232	return off;
233}
234
235/*
236 * clock_interval - is a < c < b in mod-space? Put another way, does the line
237 * from a to b cross c?
238 */
239static inline int clock_interval(size_t a, size_t b, size_t c)
240{
241	if (b < a) {
242		if (a < c || b >= c)
243			return 1;
244	} else {
245		if (a < c && b >= c)
246			return 1;
247	}
248
249	return 0;
250}
251
252/*
253 * fix_up_readers - walk the list of all readers and "fix up" any who were
254 * lapped by the writer; also do the same for the default "start head".
255 * We do this by "pulling forward" the readers and start head to the first
256 * entry after the new write head.
257 *
258 * The caller needs to hold log->mutex.
259 */
260static void fix_up_readers(struct logger_log *log, size_t len)
261{
262	size_t old = log->w_off;
263	size_t new = logger_offset(old + len);
264	struct logger_reader *reader;
265
266	if (clock_interval(old, new, log->head))
267		log->head = get_next_entry(log, log->head, len);
268
269	list_for_each_entry(reader, &log->readers, list)
270		if (clock_interval(old, new, reader->r_off))
271			reader->r_off = get_next_entry(log, reader->r_off, len);
272}
273
274/*
275 * do_write_log - writes 'len' bytes from 'buf' to 'log'
276 *
277 * The caller needs to hold log->mutex.
278 */
279static void do_write_log(struct logger_log *log, const void *buf, size_t count)
280{
281	size_t len;
282
283	len = min(count, log->size - log->w_off);
284	memcpy(log->buffer + log->w_off, buf, len);
285
286	if (count != len)
287		memcpy(log->buffer, buf + len, count - len);
288
289	log->w_off = logger_offset(log->w_off + count);
290
291}
292
293/*
294 * do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
295 * the log 'log'
296 *
297 * The caller needs to hold log->mutex.
298 *
299 * Returns 'count' on success, negative error code on failure.
300 */
301static ssize_t do_write_log_from_user(struct logger_log *log,
302				      const void __user *buf, size_t count)
303{
304	size_t len;
305
306	len = min(count, log->size - log->w_off);
307	if (len && copy_from_user(log->buffer + log->w_off, buf, len))
308		return -EFAULT;
309
310	if (count != len)
311		if (copy_from_user(log->buffer, buf + len, count - len))
312			return -EFAULT;
313
314	log->w_off = logger_offset(log->w_off + count);
315
316	return count;
317}
318
319/*
320 * logger_aio_write - our write method, implementing support for write(),
321 * writev(), and aio_write(). Writes are our fast path, and we try to optimize
322 * them above all else.
323 */
324ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
325			 unsigned long nr_segs, loff_t ppos)
326{
327	struct logger_log *log = file_get_log(iocb->ki_filp);
328	size_t orig = log->w_off;
329	struct logger_entry header;
330	struct timespec now;
331	ssize_t ret = 0;
332
333	now = current_kernel_time();
334
335	header.pid = current->tgid;
336	header.tid = current->pid;
337	header.sec = now.tv_sec;
338	header.nsec = now.tv_nsec;
339	header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
340
341	/* null writes succeed, return zero */
342	if (unlikely(!header.len))
343		return 0;
344
345	mutex_lock(&log->mutex);
346
347	/*
348	 * Fix up any readers, pulling them forward to the first readable
349	 * entry after (what will be) the new write offset. We do this now
350	 * because if we partially fail, we can end up with clobbered log
351	 * entries that encroach on readable buffer.
352	 */
353	fix_up_readers(log, sizeof(struct logger_entry) + header.len);
354
355	do_write_log(log, &header, sizeof(struct logger_entry));
356
357	while (nr_segs-- > 0) {
358		size_t len;
359		ssize_t nr;
360
361		/* figure out how much of this vector we can keep */
362		len = min_t(size_t, iov->iov_len, header.len - ret);
363
364		/* write out this segment's payload */
365		nr = do_write_log_from_user(log, iov->iov_base, len);
366		if (unlikely(nr < 0)) {
367			log->w_off = orig;
368			mutex_unlock(&log->mutex);
369			return nr;
370		}
371
372		iov++;
373		ret += nr;
374	}
375
376	mutex_unlock(&log->mutex);
377
378	/* wake up any blocked readers */
379	wake_up_interruptible(&log->wq);
380
381	return ret;
382}
383
384static struct logger_log *get_log_from_minor(int);
385
386/*
387 * logger_open - the log's open() file operation
388 *
389 * Note how near a no-op this is in the write-only case. Keep it that way!
390 */
391static int logger_open(struct inode *inode, struct file *file)
392{
393	struct logger_log *log;
394	int ret;
395
396	ret = nonseekable_open(inode, file);
397	if (ret)
398		return ret;
399
400	log = get_log_from_minor(MINOR(inode->i_rdev));
401	if (!log)
402		return -ENODEV;
403
404	if (file->f_mode & FMODE_READ) {
405		struct logger_reader *reader;
406
407		reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
408		if (!reader)
409			return -ENOMEM;
410
411		reader->log = log;
412		INIT_LIST_HEAD(&reader->list);
413
414		mutex_lock(&log->mutex);
415		reader->r_off = log->head;
416		list_add_tail(&reader->list, &log->readers);
417		mutex_unlock(&log->mutex);
418
419		file->private_data = reader;
420	} else
421		file->private_data = log;
422
423	return 0;
424}
425
426/*
427 * logger_release - the log's release file operation
428 *
429 * Note this is a total no-op in the write-only case. Keep it that way!
430 */
431static int logger_release(struct inode *ignored, struct file *file)
432{
433	if (file->f_mode & FMODE_READ) {
434		struct logger_reader *reader = file->private_data;
435		list_del(&reader->list);
436		kfree(reader);
437	}
438
439	return 0;
440}
441
442/*
443 * logger_poll - the log's poll file operation, for poll/select/epoll
444 *
445 * Note we always return POLLOUT, because you can always write() to the log.
446 * Note also that, strictly speaking, a return value of POLLIN does not
447 * guarantee that the log is readable without blocking, as there is a small
448 * chance that the writer can lap the reader in the interim between poll()
449 * returning and the read() request.
450 */
451static unsigned int logger_poll(struct file *file, poll_table *wait)
452{
453	struct logger_reader *reader;
454	struct logger_log *log;
455	unsigned int ret = POLLOUT | POLLWRNORM;
456
457	if (!(file->f_mode & FMODE_READ))
458		return ret;
459
460	reader = file->private_data;
461	log = reader->log;
462
463	poll_wait(file, &log->wq, wait);
464
465	mutex_lock(&log->mutex);
466	if (log->w_off != reader->r_off)
467		ret |= POLLIN | POLLRDNORM;
468	mutex_unlock(&log->mutex);
469
470	return ret;
471}
472
473static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
474{
475	struct logger_log *log = file_get_log(file);
476	struct logger_reader *reader;
477	long ret = -ENOTTY;
478
479	mutex_lock(&log->mutex);
480
481	switch (cmd) {
482	case LOGGER_GET_LOG_BUF_SIZE:
483		ret = log->size;
484		break;
485	case LOGGER_GET_LOG_LEN:
486		if (!(file->f_mode & FMODE_READ)) {
487			ret = -EBADF;
488			break;
489		}
490		reader = file->private_data;
491		if (log->w_off >= reader->r_off)
492			ret = log->w_off - reader->r_off;
493		else
494			ret = (log->size - reader->r_off) + log->w_off;
495		break;
496	case LOGGER_GET_NEXT_ENTRY_LEN:
497		if (!(file->f_mode & FMODE_READ)) {
498			ret = -EBADF;
499			break;
500		}
501		reader = file->private_data;
502		if (log->w_off != reader->r_off)
503			ret = get_entry_len(log, reader->r_off);
504		else
505			ret = 0;
506		break;
507	case LOGGER_FLUSH_LOG:
508		if (!(file->f_mode & FMODE_WRITE)) {
509			ret = -EBADF;
510			break;
511		}
512		list_for_each_entry(reader, &log->readers, list)
513			reader->r_off = log->w_off;
514		log->head = log->w_off;
515		ret = 0;
516		break;
517	}
518
519	mutex_unlock(&log->mutex);
520
521	return ret;
522}
523
524static const struct file_operations logger_fops = {
525	.owner = THIS_MODULE,
526	.read = logger_read,
527	.aio_write = logger_aio_write,
528	.poll = logger_poll,
529	.unlocked_ioctl = logger_ioctl,
530	.compat_ioctl = logger_ioctl,
531	.open = logger_open,
532	.release = logger_release,
533};
534
535/*
536 * Defines a log structure with name 'NAME' and a size of 'SIZE' bytes, which
537 * must be a power of two, greater than LOGGER_ENTRY_MAX_LEN, and less than
538 * LONG_MAX minus LOGGER_ENTRY_MAX_LEN.
539 */
540#define DEFINE_LOGGER_DEVICE(VAR, NAME, SIZE) \
541static unsigned char _buf_ ## VAR[SIZE]; \
542static struct logger_log VAR = { \
543	.buffer = _buf_ ## VAR, \
544	.misc = { \
545		.minor = MISC_DYNAMIC_MINOR, \
546		.name = NAME, \
547		.fops = &logger_fops, \
548		.parent = NULL, \
549	}, \
550	.wq = __WAIT_QUEUE_HEAD_INITIALIZER(VAR .wq), \
551	.readers = LIST_HEAD_INIT(VAR .readers), \
552	.mutex = __MUTEX_INITIALIZER(VAR .mutex), \
553	.w_off = 0, \
554	.head = 0, \
555	.size = SIZE, \
556};
557
558DEFINE_LOGGER_DEVICE(log_main, LOGGER_LOG_MAIN, 256*1024)
559DEFINE_LOGGER_DEVICE(log_events, LOGGER_LOG_EVENTS, 256*1024)
560DEFINE_LOGGER_DEVICE(log_radio, LOGGER_LOG_RADIO, 256*1024)
561DEFINE_LOGGER_DEVICE(log_system, LOGGER_LOG_SYSTEM, 256*1024)
562
563static struct logger_log *get_log_from_minor(int minor)
564{
565	if (log_main.misc.minor == minor)
566		return &log_main;
567	if (log_events.misc.minor == minor)
568		return &log_events;
569	if (log_radio.misc.minor == minor)
570		return &log_radio;
571	if (log_system.misc.minor == minor)
572		return &log_system;
573	return NULL;
574}
575
576static int __init init_log(struct logger_log *log)
577{
578	int ret;
579
580	ret = misc_register(&log->misc);
581	if (unlikely(ret)) {
582		printk(KERN_ERR "logger: failed to register misc "
583		       "device for log '%s'!\n", log->misc.name);
584		return ret;
585	}
586
587	printk(KERN_INFO "logger: created %luK log '%s'\n",
588	       (unsigned long) log->size >> 10, log->misc.name);
589
590	return 0;
591}
592
593static int __init logger_init(void)
594{
595	int ret;
596
597	ret = init_log(&log_main);
598	if (unlikely(ret))
599		goto out;
600
601	ret = init_log(&log_events);
602	if (unlikely(ret))
603		goto out;
604
605	ret = init_log(&log_radio);
606	if (unlikely(ret))
607		goto out;
608
609	ret = init_log(&log_system);
610	if (unlikely(ret))
611		goto out;
612
613out:
614	return ret;
615}
616device_initcall(logger_init);