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);
163 return sizeof(struct logger_entry);
166 static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
171 struct user_logger_entry_compat v1;
179 v1.nsec = entry->nsec;
181 hdr_len = sizeof(struct user_logger_entry_compat);
184 hdr_len = sizeof(struct logger_entry);
187 return copy_to_user(buf, hdr, hdr_len);
191 * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
192 * user-space buffer 'buf'. Returns 'count' on success.
194 * Caller must hold log->mutex.
196 static ssize_t do_read_log_to_user(struct logger_log *log,
197 struct logger_reader *reader,
201 struct logger_entry scratch;
202 struct logger_entry *entry;
207 * First, copy the header to userspace, using the version of
208 * the header requested
210 entry = get_entry_header(log, reader->r_off, &scratch);
211 if (copy_header_to_user(reader->r_ver, entry, buf))
214 count -= get_user_hdr_len(reader->r_ver);
215 buf += get_user_hdr_len(reader->r_ver);
216 msg_start = logger_offset(log,
217 reader->r_off + sizeof(struct logger_entry));
220 * We read from the msg in two disjoint operations. First, we read from
221 * the current msg head offset up to 'count' bytes or to the end of
222 * the log, whichever comes first.
224 len = min(count, log->size - msg_start);
225 if (copy_to_user(buf, log->buffer + msg_start, len))
229 * Second, we read any remaining bytes, starting back at the head of
233 if (copy_to_user(buf + len, log->buffer, count - len))
236 reader->r_off = logger_offset(log, reader->r_off +
237 sizeof(struct logger_entry) + count);
239 return count + get_user_hdr_len(reader->r_ver);
243 * get_next_entry_by_uid - Starting at 'off', returns an offset into
244 * 'log->buffer' which contains the first entry readable by 'euid'
246 static size_t get_next_entry_by_uid(struct logger_log *log,
247 size_t off, kuid_t euid)
249 while (off != log->w_off) {
250 struct logger_entry *entry;
251 struct logger_entry scratch;
254 entry = get_entry_header(log, off, &scratch);
256 if (uid_eq(entry->euid, euid))
259 next_len = sizeof(struct logger_entry) + entry->len;
260 off = logger_offset(log, off + next_len);
267 * logger_read - our log's read() method
272 * - If there are no log entries to read, blocks until log is written to
273 * - Atomically reads exactly one log entry
275 * Will set errno to EINVAL if read
276 * buffer is insufficient to hold next entry.
278 static ssize_t logger_read(struct file *file, char __user *buf,
279 size_t count, loff_t *pos)
281 struct logger_reader *reader = file->private_data;
282 struct logger_log *log = reader->log;
288 mutex_lock(&log->mutex);
290 prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
292 ret = (log->w_off == reader->r_off);
293 mutex_unlock(&log->mutex);
297 if (file->f_flags & O_NONBLOCK) {
302 if (signal_pending(current)) {
310 finish_wait(&log->wq, &wait);
314 mutex_lock(&log->mutex);
317 reader->r_off = get_next_entry_by_uid(log,
318 reader->r_off, current_euid());
320 /* is there still something to read or did we race? */
321 if (unlikely(log->w_off == reader->r_off)) {
322 mutex_unlock(&log->mutex);
326 /* get the size of the next entry */
327 ret = get_user_hdr_len(reader->r_ver) +
328 get_entry_msg_len(log, reader->r_off);
334 /* get exactly one entry from the log */
335 ret = do_read_log_to_user(log, reader, buf, ret);
338 mutex_unlock(&log->mutex);
344 * get_next_entry - return the offset of the first valid entry at least 'len'
347 * Caller must hold log->mutex.
349 static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
354 size_t nr = sizeof(struct logger_entry) +
355 get_entry_msg_len(log, off);
356 off = logger_offset(log, off + nr);
358 } while (count < len);
364 * is_between - is a < c < b, accounting for wrapping of a, b, and c
365 * positions in the buffer
367 * That is, if a<b, check for c between a and b
368 * and if a>b, check for c outside (not between) a and b
370 * |------- a xxxxxxxx b --------|
373 * |xxxxx b --------- a xxxxxxxxx|
377 static inline int is_between(size_t a, size_t b, size_t c)
380 /* is c between a and b? */
384 /* is c outside of b through a? */
393 * fix_up_readers - walk the list of all readers and "fix up" any who were
394 * lapped by the writer; also do the same for the default "start head".
395 * We do this by "pulling forward" the readers and start head to the first
396 * entry after the new write head.
398 * The caller needs to hold log->mutex.
400 static void fix_up_readers(struct logger_log *log, size_t len)
402 size_t old = log->w_off;
403 size_t new = logger_offset(log, old + len);
404 struct logger_reader *reader;
406 if (is_between(old, new, log->head))
407 log->head = get_next_entry(log, log->head, len);
409 list_for_each_entry(reader, &log->readers, list)
410 if (is_between(old, new, reader->r_off))
411 reader->r_off = get_next_entry(log, reader->r_off, len);
415 * do_write_log - writes 'len' bytes from 'buf' to 'log'
417 * The caller needs to hold log->mutex.
419 static void do_write_log(struct logger_log *log, const void *buf, size_t count)
423 len = min(count, log->size - log->w_off);
424 memcpy(log->buffer + log->w_off, buf, len);
427 memcpy(log->buffer, buf + len, count - len);
429 log->w_off = logger_offset(log, log->w_off + count);
434 * do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
437 * The caller needs to hold log->mutex.
439 * Returns 'count' on success, negative error code on failure.
441 static ssize_t do_write_log_from_user(struct logger_log *log,
442 const void __user *buf, size_t count)
446 len = min(count, log->size - log->w_off);
447 if (len && copy_from_user(log->buffer + log->w_off, buf, len))
451 if (copy_from_user(log->buffer, buf + len, count - len))
453 * Note that by not updating w_off, this abandons the
454 * portion of the new entry that *was* successfully
455 * copied, just above. This is intentional to avoid
456 * message corruption from missing fragments.
460 log->w_off = logger_offset(log, log->w_off + count);
466 * logger_aio_write - our write method, implementing support for write(),
467 * writev(), and aio_write(). Writes are our fast path, and we try to optimize
468 * them above all else.
470 static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
471 unsigned long nr_segs, loff_t ppos)
473 struct logger_log *log = file_get_log(iocb->ki_filp);
474 size_t orig = log->w_off;
475 struct logger_entry header;
479 now = current_kernel_time();
481 header.pid = current->tgid;
482 header.tid = current->pid;
483 header.sec = now.tv_sec;
484 header.nsec = now.tv_nsec;
485 header.euid = current_euid();
486 header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
487 header.hdr_size = sizeof(struct logger_entry);
489 /* null writes succeed, return zero */
490 if (unlikely(!header.len))
493 mutex_lock(&log->mutex);
496 * Fix up any readers, pulling them forward to the first readable
497 * entry after (what will be) the new write offset. We do this now
498 * because if we partially fail, we can end up with clobbered log
499 * entries that encroach on readable buffer.
501 fix_up_readers(log, sizeof(struct logger_entry) + header.len);
503 do_write_log(log, &header, sizeof(struct logger_entry));
505 while (nr_segs-- > 0) {
509 /* figure out how much of this vector we can keep */
510 len = min_t(size_t, iov->iov_len, header.len - ret);
512 /* write out this segment's payload */
513 nr = do_write_log_from_user(log, iov->iov_base, len);
514 if (unlikely(nr < 0)) {
516 mutex_unlock(&log->mutex);
524 mutex_unlock(&log->mutex);
526 /* wake up any blocked readers */
527 wake_up_interruptible(&log->wq);
532 static struct logger_log *get_log_from_minor(int minor)
534 struct logger_log *log;
536 list_for_each_entry(log, &log_list, logs)
537 if (log->misc.minor == minor)
543 * logger_open - the log's open() file operation
545 * Note how near a no-op this is in the write-only case. Keep it that way!
547 static int logger_open(struct inode *inode, struct file *file)
549 struct logger_log *log;
552 ret = nonseekable_open(inode, file);
556 log = get_log_from_minor(MINOR(inode->i_rdev));
560 if (file->f_mode & FMODE_READ) {
561 struct logger_reader *reader;
563 reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
569 reader->r_all = in_egroup_p(inode->i_gid) ||
572 INIT_LIST_HEAD(&reader->list);
574 mutex_lock(&log->mutex);
575 reader->r_off = log->head;
576 list_add_tail(&reader->list, &log->readers);
577 mutex_unlock(&log->mutex);
579 file->private_data = reader;
581 file->private_data = log;
587 * logger_release - the log's release file operation
589 * Note this is a total no-op in the write-only case. Keep it that way!
591 static int logger_release(struct inode *ignored, struct file *file)
593 if (file->f_mode & FMODE_READ) {
594 struct logger_reader *reader = file->private_data;
595 struct logger_log *log = reader->log;
597 mutex_lock(&log->mutex);
598 list_del(&reader->list);
599 mutex_unlock(&log->mutex);
608 * logger_poll - the log's poll file operation, for poll/select/epoll
610 * Note we always return POLLOUT, because you can always write() to the log.
611 * Note also that, strictly speaking, a return value of POLLIN does not
612 * guarantee that the log is readable without blocking, as there is a small
613 * chance that the writer can lap the reader in the interim between poll()
614 * returning and the read() request.
616 static unsigned int logger_poll(struct file *file, poll_table *wait)
618 struct logger_reader *reader;
619 struct logger_log *log;
620 unsigned int ret = POLLOUT | POLLWRNORM;
622 if (!(file->f_mode & FMODE_READ))
625 reader = file->private_data;
628 poll_wait(file, &log->wq, wait);
630 mutex_lock(&log->mutex);
632 reader->r_off = get_next_entry_by_uid(log,
633 reader->r_off, current_euid());
635 if (log->w_off != reader->r_off)
636 ret |= POLLIN | POLLRDNORM;
637 mutex_unlock(&log->mutex);
642 static long logger_set_version(struct logger_reader *reader, void __user *arg)
646 if (copy_from_user(&version, arg, sizeof(int)))
649 if ((version < 1) || (version > 2))
652 reader->r_ver = version;
656 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
658 struct logger_log *log = file_get_log(file);
659 struct logger_reader *reader;
661 void __user *argp = (void __user *) arg;
663 mutex_lock(&log->mutex);
666 case LOGGER_GET_LOG_BUF_SIZE:
669 case LOGGER_GET_LOG_LEN:
670 if (!(file->f_mode & FMODE_READ)) {
674 reader = file->private_data;
675 if (log->w_off >= reader->r_off)
676 ret = log->w_off - reader->r_off;
678 ret = (log->size - reader->r_off) + log->w_off;
680 case LOGGER_GET_NEXT_ENTRY_LEN:
681 if (!(file->f_mode & FMODE_READ)) {
685 reader = file->private_data;
688 reader->r_off = get_next_entry_by_uid(log,
689 reader->r_off, current_euid());
691 if (log->w_off != reader->r_off)
692 ret = get_user_hdr_len(reader->r_ver) +
693 get_entry_msg_len(log, reader->r_off);
697 case LOGGER_FLUSH_LOG:
698 if (!(file->f_mode & FMODE_WRITE)) {
702 if (!(in_egroup_p(file->f_dentry->d_inode->i_gid) ||
703 capable(CAP_SYSLOG))) {
707 list_for_each_entry(reader, &log->readers, list)
708 reader->r_off = log->w_off;
709 log->head = log->w_off;
712 case LOGGER_GET_VERSION:
713 if (!(file->f_mode & FMODE_READ)) {
717 reader = file->private_data;
720 case LOGGER_SET_VERSION:
721 if (!(file->f_mode & FMODE_READ)) {
725 reader = file->private_data;
726 ret = logger_set_version(reader, argp);
730 mutex_unlock(&log->mutex);
735 static const struct file_operations logger_fops = {
736 .owner = THIS_MODULE,
738 .aio_write = logger_aio_write,
740 .unlocked_ioctl = logger_ioctl,
741 .compat_ioctl = logger_ioctl,
743 .release = logger_release,
747 * Log size must must be a power of two, and greater than
748 * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
750 static int __init create_log(char *log_name, int size)
753 struct logger_log *log;
754 unsigned char *buffer;
756 buffer = vmalloc(size);
760 log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
763 goto out_free_buffer;
765 log->buffer = buffer;
767 log->misc.minor = MISC_DYNAMIC_MINOR;
768 log->misc.name = kstrdup(log_name, GFP_KERNEL);
769 if (log->misc.name == NULL) {
774 log->misc.fops = &logger_fops;
775 log->misc.parent = NULL;
777 init_waitqueue_head(&log->wq);
778 INIT_LIST_HEAD(&log->readers);
779 mutex_init(&log->mutex);
784 INIT_LIST_HEAD(&log->logs);
785 list_add_tail(&log->logs, &log_list);
787 /* finally, initialize the misc device for this log */
788 ret = misc_register(&log->misc);
790 pr_err("failed to register misc device for log '%s'!\n",
795 pr_info("created %luK log '%s'\n",
796 (unsigned long) log->size >> 10, log->misc.name);
808 static int __init logger_init(void)
812 ret = create_log(LOGGER_LOG_MAIN, 256*1024);
816 ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
820 ret = create_log(LOGGER_LOG_RADIO, 256*1024);
824 ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
832 static void __exit logger_exit(void)
834 struct logger_log *current_log, *next_log;
836 list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
837 /* we have to delete all the entry inside log_list */
838 misc_deregister(¤t_log->misc);
839 vfree(current_log->buffer);
840 kfree(current_log->misc.name);
841 list_del(¤t_log->logs);
847 device_initcall(logger_init);
848 module_exit(logger_exit);
850 MODULE_LICENSE("GPL");
851 MODULE_AUTHOR("Robert Love, <rlove@google.com>");
852 MODULE_DESCRIPTION("Android Logger");