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.
72 * @r_all: Reader can read all entries
73 * @r_ver: Reader ABI version
75 * This object lives from open to release, so we don't need additional
76 * reference counting. The structure is protected by log->mutex.
78 struct logger_reader {
79 struct logger_log *log;
80 struct list_head list;
86 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
87 static size_t logger_offset(struct logger_log *log, size_t n)
89 return n & (log->size - 1);
94 * file_get_log - Given a file structure, return the associated log
96 * This isn't aesthetic. We have several goals:
98 * 1) Need to quickly obtain the associated log during an I/O operation
99 * 2) Readers need to maintain state (logger_reader)
100 * 3) Writers need to be very fast (open() should be a near no-op)
102 * In the reader case, we can trivially go file->logger_reader->logger_log.
103 * For a writer, we don't want to maintain a logger_reader, so we just go
104 * file->logger_log. Thus what file->private_data points at depends on whether
105 * or not the file was opened for reading. This function hides that dirtiness.
107 static inline struct logger_log *file_get_log(struct file *file)
109 if (file->f_mode & FMODE_READ) {
110 struct logger_reader *reader = file->private_data;
114 return file->private_data;
118 * get_entry_header - returns a pointer to the logger_entry header within
119 * 'log' starting at offset 'off'. A temporary logger_entry 'scratch' must
120 * be provided. Typically the return value will be a pointer within
121 * 'logger->buf'. However, a pointer to 'scratch' may be returned if
122 * the log entry spans the end and beginning of the circular buffer.
124 static struct logger_entry *get_entry_header(struct logger_log *log,
125 size_t off, struct logger_entry *scratch)
127 size_t len = min(sizeof(struct logger_entry), log->size - off);
129 if (len != sizeof(struct logger_entry)) {
130 memcpy(((void *) scratch), log->buffer + off, len);
131 memcpy(((void *) scratch) + len, log->buffer,
132 sizeof(struct logger_entry) - len);
136 return (struct logger_entry *) (log->buffer + off);
140 * get_entry_msg_len - Grabs the length of the message of the entry
141 * starting from from 'off'.
143 * An entry length is 2 bytes (16 bits) in host endian order.
144 * In the log, the length does not include the size of the log entry structure.
145 * This function returns the size including the log entry structure.
147 * Caller needs to hold log->mutex.
149 static __u32 get_entry_msg_len(struct logger_log *log, size_t off)
151 struct logger_entry scratch;
152 struct logger_entry *entry;
154 entry = get_entry_header(log, off, &scratch);
158 static size_t get_user_hdr_len(int ver)
161 return sizeof(struct user_logger_entry_compat);
162 return sizeof(struct logger_entry);
165 static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
170 struct user_logger_entry_compat v1;
178 v1.nsec = entry->nsec;
180 hdr_len = sizeof(struct user_logger_entry_compat);
183 hdr_len = sizeof(struct logger_entry);
186 return copy_to_user(buf, hdr, hdr_len);
190 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
191 * user-space buffer 'buf'. Returns 'count' on success.
193 * Caller must hold log->mutex.
195 static ssize_t do_read_log_to_user(struct logger_log *log,
196 struct logger_reader *reader,
200 struct logger_entry scratch;
201 struct logger_entry *entry;
206 * First, copy the header to userspace, using the version of
207 * the header requested
209 entry = get_entry_header(log, reader->r_off, &scratch);
210 if (copy_header_to_user(reader->r_ver, entry, buf))
213 count -= get_user_hdr_len(reader->r_ver);
214 buf += get_user_hdr_len(reader->r_ver);
215 msg_start = logger_offset(log,
216 reader->r_off + sizeof(struct logger_entry));
219 * We read from the msg in two disjoint operations. First, we read from
220 * the current msg head offset up to 'count' bytes or to the end of
221 * the log, whichever comes first.
223 len = min(count, log->size - msg_start);
224 if (copy_to_user(buf, log->buffer + msg_start, len))
228 * Second, we read any remaining bytes, starting back at the head of
232 if (copy_to_user(buf + len, log->buffer, count - len))
235 reader->r_off = logger_offset(log, reader->r_off +
236 sizeof(struct logger_entry) + count);
238 return count + get_user_hdr_len(reader->r_ver);
242 * get_next_entry_by_uid - Starting at 'off', returns an offset into
243 * 'log->buffer' which contains the first entry readable by 'euid'
245 static size_t get_next_entry_by_uid(struct logger_log *log,
246 size_t off, kuid_t euid)
248 while (off != log->w_off) {
249 struct logger_entry *entry;
250 struct logger_entry scratch;
253 entry = get_entry_header(log, off, &scratch);
255 if (uid_eq(entry->euid, euid))
258 next_len = sizeof(struct logger_entry) + entry->len;
259 off = logger_offset(log, off + next_len);
266 * logger_read - our log's read() method
271 * - If there are no log entries to read, blocks until log is written to
272 * - Atomically reads exactly one log entry
274 * Will set errno to EINVAL if read
275 * buffer is insufficient to hold next entry.
277 static ssize_t logger_read(struct file *file, char __user *buf,
278 size_t count, loff_t *pos)
280 struct logger_reader *reader = file->private_data;
281 struct logger_log *log = reader->log;
287 mutex_lock(&log->mutex);
289 prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
291 ret = (log->w_off == reader->r_off);
292 mutex_unlock(&log->mutex);
296 if (file->f_flags & O_NONBLOCK) {
301 if (signal_pending(current)) {
309 finish_wait(&log->wq, &wait);
313 mutex_lock(&log->mutex);
316 reader->r_off = get_next_entry_by_uid(log,
317 reader->r_off, current_euid());
319 /* is there still something to read or did we race? */
320 if (unlikely(log->w_off == reader->r_off)) {
321 mutex_unlock(&log->mutex);
325 /* get the size of the next entry */
326 ret = get_user_hdr_len(reader->r_ver) +
327 get_entry_msg_len(log, reader->r_off);
333 /* get exactly one entry from the log */
334 ret = do_read_log_to_user(log, reader, buf, ret);
337 mutex_unlock(&log->mutex);
343 * get_next_entry - return the offset of the first valid entry at least 'len'
346 * Caller must hold log->mutex.
348 static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
353 size_t nr = sizeof(struct logger_entry) +
354 get_entry_msg_len(log, off);
355 off = logger_offset(log, off + nr);
357 } while (count < len);
363 * is_between - is a < c < b, accounting for wrapping of a, b, and c
364 * positions in the buffer
366 * That is, if a<b, check for c between a and b
367 * and if a>b, check for c outside (not between) a and b
369 * |------- a xxxxxxxx b --------|
372 * |xxxxx b --------- a xxxxxxxxx|
376 static inline int is_between(size_t a, size_t b, size_t c)
379 /* is c between a and b? */
383 /* is c outside of b through a? */
392 * fix_up_readers - walk the list of all readers and "fix up" any who were
393 * lapped by the writer; also do the same for the default "start head".
394 * We do this by "pulling forward" the readers and start head to the first
395 * entry after the new write head.
397 * The caller needs to hold log->mutex.
399 static void fix_up_readers(struct logger_log *log, size_t len)
401 size_t old = log->w_off;
402 size_t new = logger_offset(log, old + len);
403 struct logger_reader *reader;
405 if (is_between(old, new, log->head))
406 log->head = get_next_entry(log, log->head, len);
408 list_for_each_entry(reader, &log->readers, list)
409 if (is_between(old, new, reader->r_off))
410 reader->r_off = get_next_entry(log, reader->r_off, len);
414 * logger_write_iter - our write method, implementing support for write(),
415 * writev(), and aio_write(). Writes are our fast path, and we try to optimize
416 * them above all else.
418 static ssize_t logger_write_iter(struct kiocb *iocb, struct iov_iter *from)
420 struct logger_log *log = file_get_log(iocb->ki_filp);
421 struct logger_entry header;
425 count = min_t(size_t, iocb->ki_nbytes, LOGGER_ENTRY_MAX_PAYLOAD);
427 now = current_kernel_time();
429 header.pid = current->tgid;
430 header.tid = current->pid;
431 header.sec = now.tv_sec;
432 header.nsec = now.tv_nsec;
433 header.euid = current_euid();
435 header.hdr_size = sizeof(struct logger_entry);
437 /* null writes succeed, return zero */
438 if (unlikely(!header.len))
441 mutex_lock(&log->mutex);
444 * Fix up any readers, pulling them forward to the first readable
445 * entry after (what will be) the new write offset. We do this now
446 * because if we partially fail, we can end up with clobbered log
447 * entries that encroach on readable buffer.
449 fix_up_readers(log, sizeof(struct logger_entry) + header.len);
451 len = min(sizeof(header), log->size - log->w_off);
452 memcpy(log->buffer + log->w_off, &header, len);
453 memcpy(log->buffer, (char *)&header + len, sizeof(header) - len);
455 len = min(count, log->size - log->w_off);
457 if (copy_from_iter(log->buffer + log->w_off, len, from) != len) {
459 * Note that by not updating w_off, this abandons the
460 * portion of the new entry that *was* successfully
461 * copied, just above. This is intentional to avoid
462 * message corruption from missing fragments.
464 mutex_unlock(&log->mutex);
468 if (copy_from_iter(log->buffer, count - len, from) != count - len) {
469 mutex_unlock(&log->mutex);
473 log->w_off = logger_offset(log, log->w_off + count);
474 mutex_unlock(&log->mutex);
476 /* wake up any blocked readers */
477 wake_up_interruptible(&log->wq);
482 static struct logger_log *get_log_from_minor(int minor)
484 struct logger_log *log;
486 list_for_each_entry(log, &log_list, logs)
487 if (log->misc.minor == minor)
493 * logger_open - the log's open() file operation
495 * Note how near a no-op this is in the write-only case. Keep it that way!
497 static int logger_open(struct inode *inode, struct file *file)
499 struct logger_log *log;
502 ret = nonseekable_open(inode, file);
506 log = get_log_from_minor(MINOR(inode->i_rdev));
510 if (file->f_mode & FMODE_READ) {
511 struct logger_reader *reader;
513 reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
519 reader->r_all = in_egroup_p(inode->i_gid) ||
522 INIT_LIST_HEAD(&reader->list);
524 mutex_lock(&log->mutex);
525 reader->r_off = log->head;
526 list_add_tail(&reader->list, &log->readers);
527 mutex_unlock(&log->mutex);
529 file->private_data = reader;
531 file->private_data = log;
537 * logger_release - the log's release file operation
539 * Note this is a total no-op in the write-only case. Keep it that way!
541 static int logger_release(struct inode *ignored, struct file *file)
543 if (file->f_mode & FMODE_READ) {
544 struct logger_reader *reader = file->private_data;
545 struct logger_log *log = reader->log;
547 mutex_lock(&log->mutex);
548 list_del(&reader->list);
549 mutex_unlock(&log->mutex);
558 * logger_poll - the log's poll file operation, for poll/select/epoll
560 * Note we always return POLLOUT, because you can always write() to the log.
561 * Note also that, strictly speaking, a return value of POLLIN does not
562 * guarantee that the log is readable without blocking, as there is a small
563 * chance that the writer can lap the reader in the interim between poll()
564 * returning and the read() request.
566 static unsigned int logger_poll(struct file *file, poll_table *wait)
568 struct logger_reader *reader;
569 struct logger_log *log;
570 unsigned int ret = POLLOUT | POLLWRNORM;
572 if (!(file->f_mode & FMODE_READ))
575 reader = file->private_data;
578 poll_wait(file, &log->wq, wait);
580 mutex_lock(&log->mutex);
582 reader->r_off = get_next_entry_by_uid(log,
583 reader->r_off, current_euid());
585 if (log->w_off != reader->r_off)
586 ret |= POLLIN | POLLRDNORM;
587 mutex_unlock(&log->mutex);
592 static long logger_set_version(struct logger_reader *reader, void __user *arg)
596 if (copy_from_user(&version, arg, sizeof(int)))
599 if ((version < 1) || (version > 2))
602 reader->r_ver = version;
606 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
608 struct logger_log *log = file_get_log(file);
609 struct logger_reader *reader;
611 void __user *argp = (void __user *) arg;
613 mutex_lock(&log->mutex);
616 case LOGGER_GET_LOG_BUF_SIZE:
619 case LOGGER_GET_LOG_LEN:
620 if (!(file->f_mode & FMODE_READ)) {
624 reader = file->private_data;
625 if (log->w_off >= reader->r_off)
626 ret = log->w_off - reader->r_off;
628 ret = (log->size - reader->r_off) + log->w_off;
630 case LOGGER_GET_NEXT_ENTRY_LEN:
631 if (!(file->f_mode & FMODE_READ)) {
635 reader = file->private_data;
638 reader->r_off = get_next_entry_by_uid(log,
639 reader->r_off, current_euid());
641 if (log->w_off != reader->r_off)
642 ret = get_user_hdr_len(reader->r_ver) +
643 get_entry_msg_len(log, reader->r_off);
647 case LOGGER_FLUSH_LOG:
648 if (!(file->f_mode & FMODE_WRITE)) {
652 if (!(in_egroup_p(file_inode(file)->i_gid) ||
653 capable(CAP_SYSLOG))) {
657 list_for_each_entry(reader, &log->readers, list)
658 reader->r_off = log->w_off;
659 log->head = log->w_off;
662 case LOGGER_GET_VERSION:
663 if (!(file->f_mode & FMODE_READ)) {
667 reader = file->private_data;
670 case LOGGER_SET_VERSION:
671 if (!(file->f_mode & FMODE_READ)) {
675 reader = file->private_data;
676 ret = logger_set_version(reader, argp);
680 mutex_unlock(&log->mutex);
685 static const struct file_operations logger_fops = {
686 .owner = THIS_MODULE,
688 .write_iter = logger_write_iter,
690 .unlocked_ioctl = logger_ioctl,
691 .compat_ioctl = logger_ioctl,
693 .release = logger_release,
697 * Log size must must be a power of two, and greater than
698 * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
700 static int __init create_log(char *log_name, int size)
703 struct logger_log *log;
704 unsigned char *buffer;
706 buffer = vmalloc(size);
710 log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
713 goto out_free_buffer;
715 log->buffer = buffer;
717 log->misc.minor = MISC_DYNAMIC_MINOR;
718 log->misc.name = kstrdup(log_name, GFP_KERNEL);
719 if (log->misc.name == NULL) {
724 log->misc.fops = &logger_fops;
725 log->misc.parent = NULL;
727 init_waitqueue_head(&log->wq);
728 INIT_LIST_HEAD(&log->readers);
729 mutex_init(&log->mutex);
734 INIT_LIST_HEAD(&log->logs);
735 list_add_tail(&log->logs, &log_list);
737 /* finally, initialize the misc device for this log */
738 ret = misc_register(&log->misc);
740 pr_err("failed to register misc device for log '%s'!\n",
742 goto out_free_misc_name;
745 pr_info("created %luK log '%s'\n",
746 (unsigned long) log->size >> 10, log->misc.name);
751 kfree(log->misc.name);
761 static int __init logger_init(void)
765 ret = create_log(LOGGER_LOG_MAIN, 256*1024);
769 ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
773 ret = create_log(LOGGER_LOG_RADIO, 256*1024);
777 ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
785 static void __exit logger_exit(void)
787 struct logger_log *current_log, *next_log;
789 list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
790 /* we have to delete all the entry inside log_list */
791 misc_deregister(¤t_log->misc);
792 vfree(current_log->buffer);
793 kfree(current_log->misc.name);
794 list_del(¤t_log->logs);
800 device_initcall(logger_init);
801 module_exit(logger_exit);
803 MODULE_LICENSE("GPL");
804 MODULE_AUTHOR("Robert Love, <rlove@google.com>");
805 MODULE_DESCRIPTION("Android Logger");