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 #include <linux/sched.h>
21 #include <linux/module.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>
30 #include <asm/ioctls.h>
33 * struct logger_log - represents a specific log, such as 'main' or 'radio'
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
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 */
51 * struct logger_reader - a logging device open for reading
53 * This object lives from open to release, so we don't need additional
54 * reference counting. The structure is protected by log->mutex.
56 struct 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 */
62 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
63 #define logger_offset(n) ((n) & (log->size - 1))
66 * file_get_log - Given a file structure, return the associated log
68 * This isn't aesthetic. We have several goals:
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)
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.
79 static inline struct logger_log *file_get_log(struct file *file)
81 if (file->f_mode & FMODE_READ) {
82 struct logger_reader *reader = file->private_data;
85 return file->private_data;
89 * get_entry_len - Grabs the length of the payload of the next entry starting
92 * Caller needs to hold log->mutex.
94 static __u32 get_entry_len(struct logger_log *log, size_t off)
98 switch (log->size - off) {
100 memcpy(&val, log->buffer + off, 1);
101 memcpy(((char *) &val) + 1, log->buffer, 1);
104 memcpy(&val, log->buffer + off, 2);
107 return sizeof(struct logger_entry) + val;
111 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
112 * user-space buffer 'buf'. Returns 'count' on success.
114 * Caller must hold log->mutex.
116 static ssize_t do_read_log_to_user(struct logger_log *log,
117 struct logger_reader *reader,
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.
128 len = min(count, log->size - reader->r_off);
129 if (copy_to_user(buf, log->buffer + reader->r_off, len))
133 * Second, we read any remaining bytes, starting back at the head of
137 if (copy_to_user(buf + len, log->buffer, count - len))
140 reader->r_off = logger_offset(reader->r_off + count);
146 * logger_read - our log's read() method
151 * - If there are no log entries to read, blocks until log is written to
152 * - Atomically reads exactly one log entry
154 * Optimal read size is LOGGER_ENTRY_MAX_LEN. Will set errno to EINVAL if read
155 * buffer is insufficient to hold next entry.
157 static ssize_t logger_read(struct file *file, char __user *buf,
158 size_t count, loff_t *pos)
160 struct logger_reader *reader = file->private_data;
161 struct logger_log *log = reader->log;
167 prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
169 mutex_lock(&log->mutex);
170 ret = (log->w_off == reader->r_off);
171 mutex_unlock(&log->mutex);
175 if (file->f_flags & O_NONBLOCK) {
180 if (signal_pending(current)) {
188 finish_wait(&log->wq, &wait);
192 mutex_lock(&log->mutex);
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);
200 /* get the size of the next entry */
201 ret = get_entry_len(log, reader->r_off);
207 /* get exactly one entry from the log */
208 ret = do_read_log_to_user(log, reader, buf, ret);
211 mutex_unlock(&log->mutex);
217 * get_next_entry - return the offset of the first valid entry at least 'len'
220 * Caller must hold log->mutex.
222 static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
227 size_t nr = get_entry_len(log, off);
228 off = logger_offset(off + nr);
230 } while (count < len);
236 * clock_interval - is a < c < b in mod-space? Put another way, does the line
237 * from a to b cross c?
239 static inline int clock_interval(size_t a, size_t b, size_t c)
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.
258 * The caller needs to hold log->mutex.
260 static void fix_up_readers(struct logger_log *log, size_t len)
262 size_t old = log->w_off;
263 size_t new = logger_offset(old + len);
264 struct logger_reader *reader;
266 if (clock_interval(old, new, log->head))
267 log->head = get_next_entry(log, log->head, len);
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);
275 * do_write_log - writes 'len' bytes from 'buf' to 'log'
277 * The caller needs to hold log->mutex.
279 static void do_write_log(struct logger_log *log, const void *buf, size_t count)
283 len = min(count, log->size - log->w_off);
284 memcpy(log->buffer + log->w_off, buf, len);
287 memcpy(log->buffer, buf + len, count - len);
289 log->w_off = logger_offset(log->w_off + count);
294 * do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
297 * The caller needs to hold log->mutex.
299 * Returns 'count' on success, negative error code on failure.
301 static ssize_t do_write_log_from_user(struct logger_log *log,
302 const void __user *buf, size_t count)
306 len = min(count, log->size - log->w_off);
307 if (len && copy_from_user(log->buffer + log->w_off, buf, len))
311 if (copy_from_user(log->buffer, buf + len, count - len))
314 log->w_off = logger_offset(log->w_off + count);
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.
324 ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
325 unsigned long nr_segs, loff_t ppos)
327 struct logger_log *log = file_get_log(iocb->ki_filp);
328 size_t orig = log->w_off;
329 struct logger_entry header;
333 now = current_kernel_time();
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);
341 /* null writes succeed, return zero */
342 if (unlikely(!header.len))
345 mutex_lock(&log->mutex);
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.
353 fix_up_readers(log, sizeof(struct logger_entry) + header.len);
355 do_write_log(log, &header, sizeof(struct logger_entry));
357 while (nr_segs-- > 0) {
361 /* figure out how much of this vector we can keep */
362 len = min_t(size_t, iov->iov_len, header.len - ret);
364 /* write out this segment's payload */
365 nr = do_write_log_from_user(log, iov->iov_base, len);
366 if (unlikely(nr < 0)) {
368 mutex_unlock(&log->mutex);
376 mutex_unlock(&log->mutex);
378 /* wake up any blocked readers */
379 wake_up_interruptible(&log->wq);
384 static struct logger_log *get_log_from_minor(int);
387 * logger_open - the log's open() file operation
389 * Note how near a no-op this is in the write-only case. Keep it that way!
391 static int logger_open(struct inode *inode, struct file *file)
393 struct logger_log *log;
396 ret = nonseekable_open(inode, file);
400 log = get_log_from_minor(MINOR(inode->i_rdev));
404 if (file->f_mode & FMODE_READ) {
405 struct logger_reader *reader;
407 reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
412 INIT_LIST_HEAD(&reader->list);
414 mutex_lock(&log->mutex);
415 reader->r_off = log->head;
416 list_add_tail(&reader->list, &log->readers);
417 mutex_unlock(&log->mutex);
419 file->private_data = reader;
421 file->private_data = log;
427 * logger_release - the log's release file operation
429 * Note this is a total no-op in the write-only case. Keep it that way!
431 static int logger_release(struct inode *ignored, struct file *file)
433 if (file->f_mode & FMODE_READ) {
434 struct logger_reader *reader = file->private_data;
435 list_del(&reader->list);
443 * logger_poll - the log's poll file operation, for poll/select/epoll
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.
451 static unsigned int logger_poll(struct file *file, poll_table *wait)
453 struct logger_reader *reader;
454 struct logger_log *log;
455 unsigned int ret = POLLOUT | POLLWRNORM;
457 if (!(file->f_mode & FMODE_READ))
460 reader = file->private_data;
463 poll_wait(file, &log->wq, wait);
465 mutex_lock(&log->mutex);
466 if (log->w_off != reader->r_off)
467 ret |= POLLIN | POLLRDNORM;
468 mutex_unlock(&log->mutex);
473 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
475 struct logger_log *log = file_get_log(file);
476 struct logger_reader *reader;
479 mutex_lock(&log->mutex);
482 case LOGGER_GET_LOG_BUF_SIZE:
485 case LOGGER_GET_LOG_LEN:
486 if (!(file->f_mode & FMODE_READ)) {
490 reader = file->private_data;
491 if (log->w_off >= reader->r_off)
492 ret = log->w_off - reader->r_off;
494 ret = (log->size - reader->r_off) + log->w_off;
496 case LOGGER_GET_NEXT_ENTRY_LEN:
497 if (!(file->f_mode & FMODE_READ)) {
501 reader = file->private_data;
502 if (log->w_off != reader->r_off)
503 ret = get_entry_len(log, reader->r_off);
507 case LOGGER_FLUSH_LOG:
508 if (!(file->f_mode & FMODE_WRITE)) {
512 list_for_each_entry(reader, &log->readers, list)
513 reader->r_off = log->w_off;
514 log->head = log->w_off;
519 mutex_unlock(&log->mutex);
524 static const struct file_operations logger_fops = {
525 .owner = THIS_MODULE,
527 .aio_write = logger_aio_write,
529 .unlocked_ioctl = logger_ioctl,
530 .compat_ioctl = logger_ioctl,
532 .release = logger_release,
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.
540 #define DEFINE_LOGGER_DEVICE(VAR, NAME, SIZE) \
541 static unsigned char _buf_ ## VAR[SIZE]; \
542 static struct logger_log VAR = { \
543 .buffer = _buf_ ## VAR, \
545 .minor = MISC_DYNAMIC_MINOR, \
547 .fops = &logger_fops, \
550 .wq = __WAIT_QUEUE_HEAD_INITIALIZER(VAR .wq), \
551 .readers = LIST_HEAD_INIT(VAR .readers), \
552 .mutex = __MUTEX_INITIALIZER(VAR .mutex), \
558 DEFINE_LOGGER_DEVICE(log_main, LOGGER_LOG_MAIN, 64*1024)
559 DEFINE_LOGGER_DEVICE(log_events, LOGGER_LOG_EVENTS, 256*1024)
560 DEFINE_LOGGER_DEVICE(log_radio, LOGGER_LOG_RADIO, 64*1024)
561 DEFINE_LOGGER_DEVICE(log_system, LOGGER_LOG_SYSTEM, 64*1024)
563 static struct logger_log *get_log_from_minor(int minor)
565 if (log_main.misc.minor == minor)
567 if (log_events.misc.minor == minor)
569 if (log_radio.misc.minor == minor)
571 if (log_system.misc.minor == minor)
576 static int __init init_log(struct logger_log *log)
580 ret = misc_register(&log->misc);
582 printk(KERN_ERR "logger: failed to register misc "
583 "device for log '%s'!\n", log->misc.name);
587 printk(KERN_INFO "logger: created %luK log '%s'\n",
588 (unsigned long) log->size >> 10, log->misc.name);
593 static int __init logger_init(void)
597 ret = init_log(&log_main);
601 ret = init_log(&log_events);
605 ret = init_log(&log_radio);
609 ret = init_log(&log_system);
616 device_initcall(logger_init);