2 * drivers/misc/logger.c
6 * Copyright (C) 2007-2008 Google, Inc.
8 * Robert Love <rlove@google.com>
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.
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.
20 #define pr_fmt(fmt) "logger: " fmt
22 #include <linux/sched.h>
23 #include <linux/module.h>
25 #include <linux/miscdevice.h>
26 #include <linux/uaccess.h>
27 #include <linux/poll.h>
28 #include <linux/slab.h>
29 #include <linux/time.h>
30 #include <linux/vmalloc.h>
31 #include <linux/aio.h>
34 #include <asm/ioctls.h>
37 * struct logger_log - represents a specific log, such as 'main' or 'radio'
38 * @buffer: The actual ring buffer
39 * @misc: The "misc" device representing the log
40 * @wq: The wait queue for @readers
41 * @readers: This log's readers
42 * @mutex: The mutex that protects the @buffer
43 * @w_off: The current write head offset
44 * @head: The head, or location that readers start reading at.
45 * @size: The size of the log
46 * @logs: The list of log channels
48 * This structure lives from module insertion until module removal, so it does
49 * not need additional reference counting. The structure is protected by the
53 unsigned char *buffer;
54 struct miscdevice misc;
56 struct list_head readers;
61 struct list_head logs;
64 static LIST_HEAD(log_list);
68 * struct logger_reader - a logging device open for reading
69 * @log: The associated log
70 * @list: The associated entry in @logger_log's list
71 * @r_off: The current read head offset.
73 * This object lives from open to release, so we don't need additional
74 * reference counting. The structure is protected by log->mutex.
76 struct logger_reader {
77 struct logger_log *log;
78 struct list_head list;
82 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
83 static size_t logger_offset(struct logger_log *log, size_t n)
85 return n & (log->size - 1);
90 * file_get_log - Given a file structure, return the associated log
92 * This isn't aesthetic. We have several goals:
94 * 1) Need to quickly obtain the associated log during an I/O operation
95 * 2) Readers need to maintain state (logger_reader)
96 * 3) Writers need to be very fast (open() should be a near no-op)
98 * In the reader case, we can trivially go file->logger_reader->logger_log.
99 * For a writer, we don't want to maintain a logger_reader, so we just go
100 * file->logger_log. Thus what file->private_data points at depends on whether
101 * or not the file was opened for reading. This function hides that dirtiness.
103 static inline struct logger_log *file_get_log(struct file *file)
105 if (file->f_mode & FMODE_READ) {
106 struct logger_reader *reader = file->private_data;
109 return file->private_data;
113 * get_entry_len - Grabs the length of the payload of the next entry starting
116 * An entry length is 2 bytes (16 bits) in host endian order.
117 * In the log, the length does not include the size of the log entry structure.
118 * This function returns the size including the log entry structure.
120 * Caller needs to hold log->mutex.
122 static __u32 get_entry_len(struct logger_log *log, size_t off)
126 /* copy 2 bytes from buffer, in memcpy order, */
127 /* handling possible wrap at end of buffer */
129 ((__u8 *)&val)[0] = log->buffer[off];
130 if (likely(off+1 < log->size))
131 ((__u8 *)&val)[1] = log->buffer[off+1];
133 ((__u8 *)&val)[1] = log->buffer[0];
135 return sizeof(struct logger_entry) + val;
139 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
140 * user-space buffer 'buf'. Returns 'count' on success.
142 * Caller must hold log->mutex.
144 static ssize_t do_read_log_to_user(struct logger_log *log,
145 struct logger_reader *reader,
152 * We read from the log in two disjoint operations. First, we read from
153 * the current read head offset up to 'count' bytes or to the end of
154 * the log, whichever comes first.
156 len = min(count, log->size - reader->r_off);
157 if (copy_to_user(buf, log->buffer + reader->r_off, len))
161 * Second, we read any remaining bytes, starting back at the head of
165 if (copy_to_user(buf + len, log->buffer, count - len))
168 reader->r_off = logger_offset(log, reader->r_off + count);
174 * logger_read - our log's read() method
179 * - If there are no log entries to read, blocks until log is written to
180 * - Atomically reads exactly one log entry
182 * Optimal read size is LOGGER_ENTRY_MAX_LEN. Will set errno to EINVAL if read
183 * buffer is insufficient to hold next entry.
185 static ssize_t logger_read(struct file *file, char __user *buf,
186 size_t count, loff_t *pos)
188 struct logger_reader *reader = file->private_data;
189 struct logger_log *log = reader->log;
195 mutex_lock(&log->mutex);
197 prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
199 ret = (log->w_off == reader->r_off);
200 mutex_unlock(&log->mutex);
204 if (file->f_flags & O_NONBLOCK) {
209 if (signal_pending(current)) {
217 finish_wait(&log->wq, &wait);
221 mutex_lock(&log->mutex);
223 /* is there still something to read or did we race? */
224 if (unlikely(log->w_off == reader->r_off)) {
225 mutex_unlock(&log->mutex);
229 /* get the size of the next entry */
230 ret = get_entry_len(log, reader->r_off);
236 /* get exactly one entry from the log */
237 ret = do_read_log_to_user(log, reader, buf, ret);
240 mutex_unlock(&log->mutex);
246 * get_next_entry - return the offset of the first valid entry at least 'len'
249 * Caller must hold log->mutex.
251 static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
256 size_t nr = get_entry_len(log, off);
257 off = logger_offset(log, off + nr);
259 } while (count < len);
265 * is_between - is a < c < b, accounting for wrapping of a, b, and c
266 * positions in the buffer
268 * That is, if a<b, check for c between a and b
269 * and if a>b, check for c outside (not between) a and b
271 * |------- a xxxxxxxx b --------|
274 * |xxxxx b --------- a xxxxxxxxx|
278 static inline int is_between(size_t a, size_t b, size_t c)
281 /* is c between a and b? */
285 /* is c outside of b through a? */
294 * fix_up_readers - walk the list of all readers and "fix up" any who were
295 * lapped by the writer; also do the same for the default "start head".
296 * We do this by "pulling forward" the readers and start head to the first
297 * entry after the new write head.
299 * The caller needs to hold log->mutex.
301 static void fix_up_readers(struct logger_log *log, size_t len)
303 size_t old = log->w_off;
304 size_t new = logger_offset(log, old + len);
305 struct logger_reader *reader;
307 if (is_between(old, new, log->head))
308 log->head = get_next_entry(log, log->head, len);
310 list_for_each_entry(reader, &log->readers, list)
311 if (is_between(old, new, reader->r_off))
312 reader->r_off = get_next_entry(log, reader->r_off, len);
316 * do_write_log - writes 'len' bytes from 'buf' to 'log'
318 * The caller needs to hold log->mutex.
320 static void do_write_log(struct logger_log *log, const void *buf, size_t count)
324 len = min(count, log->size - log->w_off);
325 memcpy(log->buffer + log->w_off, buf, len);
328 memcpy(log->buffer, buf + len, count - len);
330 log->w_off = logger_offset(log, log->w_off + count);
335 * do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
338 * The caller needs to hold log->mutex.
340 * Returns 'count' on success, negative error code on failure.
342 static ssize_t do_write_log_from_user(struct logger_log *log,
343 const void __user *buf, size_t count)
347 len = min(count, log->size - log->w_off);
348 if (len && copy_from_user(log->buffer + log->w_off, buf, len))
352 if (copy_from_user(log->buffer, buf + len, count - len))
354 * Note that by not updating w_off, this abandons the
355 * portion of the new entry that *was* successfully
356 * copied, just above. This is intentional to avoid
357 * message corruption from missing fragments.
361 log->w_off = logger_offset(log, log->w_off + count);
367 * logger_aio_write - our write method, implementing support for write(),
368 * writev(), and aio_write(). Writes are our fast path, and we try to optimize
369 * them above all else.
371 static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
372 unsigned long nr_segs, loff_t ppos)
374 struct logger_log *log = file_get_log(iocb->ki_filp);
375 size_t orig = log->w_off;
376 struct logger_entry header;
380 now = current_kernel_time();
382 header.pid = current->tgid;
383 header.tid = current->pid;
384 header.sec = now.tv_sec;
385 header.nsec = now.tv_nsec;
386 header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
388 /* null writes succeed, return zero */
389 if (unlikely(!header.len))
392 mutex_lock(&log->mutex);
395 * Fix up any readers, pulling them forward to the first readable
396 * entry after (what will be) the new write offset. We do this now
397 * because if we partially fail, we can end up with clobbered log
398 * entries that encroach on readable buffer.
400 fix_up_readers(log, sizeof(struct logger_entry) + header.len);
402 do_write_log(log, &header, sizeof(struct logger_entry));
404 while (nr_segs-- > 0) {
408 /* figure out how much of this vector we can keep */
409 len = min_t(size_t, iov->iov_len, header.len - ret);
411 /* write out this segment's payload */
412 nr = do_write_log_from_user(log, iov->iov_base, len);
413 if (unlikely(nr < 0)) {
415 mutex_unlock(&log->mutex);
423 mutex_unlock(&log->mutex);
425 /* wake up any blocked readers */
426 wake_up_interruptible(&log->wq);
431 static struct logger_log *get_log_from_minor(int minor)
433 struct logger_log *log;
435 list_for_each_entry(log, &log_list, logs)
436 if (log->misc.minor == minor)
442 * logger_open - the log's open() file operation
444 * Note how near a no-op this is in the write-only case. Keep it that way!
446 static int logger_open(struct inode *inode, struct file *file)
448 struct logger_log *log;
451 ret = nonseekable_open(inode, file);
455 log = get_log_from_minor(MINOR(inode->i_rdev));
459 if (file->f_mode & FMODE_READ) {
460 struct logger_reader *reader;
462 reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
467 INIT_LIST_HEAD(&reader->list);
469 mutex_lock(&log->mutex);
470 reader->r_off = log->head;
471 list_add_tail(&reader->list, &log->readers);
472 mutex_unlock(&log->mutex);
474 file->private_data = reader;
476 file->private_data = log;
482 * logger_release - the log's release file operation
484 * Note this is a total no-op in the write-only case. Keep it that way!
486 static int logger_release(struct inode *ignored, struct file *file)
488 if (file->f_mode & FMODE_READ) {
489 struct logger_reader *reader = file->private_data;
490 struct logger_log *log = reader->log;
492 mutex_lock(&log->mutex);
493 list_del(&reader->list);
494 mutex_unlock(&log->mutex);
503 * logger_poll - the log's poll file operation, for poll/select/epoll
505 * Note we always return POLLOUT, because you can always write() to the log.
506 * Note also that, strictly speaking, a return value of POLLIN does not
507 * guarantee that the log is readable without blocking, as there is a small
508 * chance that the writer can lap the reader in the interim between poll()
509 * returning and the read() request.
511 static unsigned int logger_poll(struct file *file, poll_table *wait)
513 struct logger_reader *reader;
514 struct logger_log *log;
515 unsigned int ret = POLLOUT | POLLWRNORM;
517 if (!(file->f_mode & FMODE_READ))
520 reader = file->private_data;
523 poll_wait(file, &log->wq, wait);
525 mutex_lock(&log->mutex);
526 if (log->w_off != reader->r_off)
527 ret |= POLLIN | POLLRDNORM;
528 mutex_unlock(&log->mutex);
533 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
535 struct logger_log *log = file_get_log(file);
536 struct logger_reader *reader;
539 mutex_lock(&log->mutex);
542 case LOGGER_GET_LOG_BUF_SIZE:
545 case LOGGER_GET_LOG_LEN:
546 if (!(file->f_mode & FMODE_READ)) {
550 reader = file->private_data;
551 if (log->w_off >= reader->r_off)
552 ret = log->w_off - reader->r_off;
554 ret = (log->size - reader->r_off) + log->w_off;
556 case LOGGER_GET_NEXT_ENTRY_LEN:
557 if (!(file->f_mode & FMODE_READ)) {
561 reader = file->private_data;
562 if (log->w_off != reader->r_off)
563 ret = get_entry_len(log, reader->r_off);
567 case LOGGER_FLUSH_LOG:
568 if (!(file->f_mode & FMODE_WRITE)) {
572 list_for_each_entry(reader, &log->readers, list)
573 reader->r_off = log->w_off;
574 log->head = log->w_off;
579 mutex_unlock(&log->mutex);
584 static const struct file_operations logger_fops = {
585 .owner = THIS_MODULE,
587 .aio_write = logger_aio_write,
589 .unlocked_ioctl = logger_ioctl,
590 .compat_ioctl = logger_ioctl,
592 .release = logger_release,
596 * Log size must be a power of two, greater than LOGGER_ENTRY_MAX_LEN,
597 * and less than LONG_MAX minus LOGGER_ENTRY_MAX_LEN.
599 static int __init create_log(char *log_name, int size)
602 struct logger_log *log;
603 unsigned char *buffer;
605 buffer = vmalloc(size);
609 log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
612 goto out_free_buffer;
614 log->buffer = buffer;
616 log->misc.minor = MISC_DYNAMIC_MINOR;
617 log->misc.name = kstrdup(log_name, GFP_KERNEL);
618 if (log->misc.name == NULL) {
623 log->misc.fops = &logger_fops;
624 log->misc.parent = NULL;
626 init_waitqueue_head(&log->wq);
627 INIT_LIST_HEAD(&log->readers);
628 mutex_init(&log->mutex);
633 INIT_LIST_HEAD(&log->logs);
634 list_add_tail(&log->logs, &log_list);
636 /* finally, initialize the misc device for this log */
637 ret = misc_register(&log->misc);
639 pr_err("failed to register misc device for log '%s'!\n",
644 pr_info("created %luK log '%s'\n",
645 (unsigned long) log->size >> 10, log->misc.name);
657 static int __init logger_init(void)
661 ret = create_log(LOGGER_LOG_MAIN, 256*1024);
665 ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
669 ret = create_log(LOGGER_LOG_RADIO, 256*1024);
673 ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
681 static void __exit logger_exit(void)
683 struct logger_log *current_log, *next_log;
685 list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
686 /* we have to delete all the entry inside log_list */
687 misc_deregister(¤t_log->misc);
688 vfree(current_log->buffer);
689 kfree(current_log->misc.name);
690 list_del(¤t_log->logs);
696 device_initcall(logger_init);
697 module_exit(logger_exit);
699 MODULE_LICENSE("GPL");
700 MODULE_AUTHOR("Robert Love, <rlove@google.com>");
701 MODULE_DESCRIPTION("Android Logger");