blob: f7b8237d5be74bd284c2fe561defb3b9902b224d [file] [log] [blame]
/*
* drivers/misc/logger.c
*
* A Logging Subsystem
*
* Copyright (C) 2007-2008 Google, Inc.
*
* Robert Love <rlove@google.com>
*
* This software is licensed under the terms of the GNU General Public
* License version 2, as published by the Free Software Foundation, and
* may be copied, distributed, and modified under those terms.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#define pr_fmt(fmt) "logger: " fmt
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/vmalloc.h>
#include "logger.h"
#include <asm/ioctls.h>
/*
* struct logger_log - represents a specific log, such as 'main' or 'radio'
*
* This structure lives from module insertion until module removal, so it does
* not need additional reference counting. The structure is protected by the
* mutex 'mutex'.
*/
struct logger_log {
unsigned char *buffer;/* the ring buffer itself */
struct miscdevice misc; /* misc device representing the log */
wait_queue_head_t wq; /* wait queue for readers */
struct list_head readers; /* this log's readers */
struct mutex mutex; /* mutex protecting buffer */
size_t w_off; /* current write head offset */
size_t head; /* new readers start here */
size_t size; /* size of the log */
struct list_head logs; /* list of log channels (myself)*/
};
static LIST_HEAD(log_list);
/*
* struct logger_reader - a logging device open for reading
*
* This object lives from open to release, so we don't need additional
* reference counting. The structure is protected by log->mutex.
*/
struct logger_reader {
struct logger_log *log; /* associated log */
struct list_head list; /* entry in logger_log's list */
size_t r_off; /* current read head offset */
};
/* logger_offset - returns index 'n' into the log via (optimized) modulus */
static size_t logger_offset(struct logger_log *log, size_t n)
{
return n & (log->size - 1);
}
/*
* file_get_log - Given a file structure, return the associated log
*
* This isn't aesthetic. We have several goals:
*
* 1) Need to quickly obtain the associated log during an I/O operation
* 2) Readers need to maintain state (logger_reader)
* 3) Writers need to be very fast (open() should be a near no-op)
*
* In the reader case, we can trivially go file->logger_reader->logger_log.
* For a writer, we don't want to maintain a logger_reader, so we just go
* file->logger_log. Thus what file->private_data points at depends on whether
* or not the file was opened for reading. This function hides that dirtiness.
*/
static inline struct logger_log *file_get_log(struct file *file)
{
if (file->f_mode & FMODE_READ) {
struct logger_reader *reader = file->private_data;
return reader->log;
} else
return file->private_data;
}
/*
* get_entry_len - Grabs the length of the payload of the next entry starting
* from 'off'.
*
* An entry length is 2 bytes (16 bits) in host endian order.
* In the log, the length does not include the size of the log entry structure.
* This function returns the size including the log entry structure.
*
* Caller needs to hold log->mutex.
*/
static __u32 get_entry_len(struct logger_log *log, size_t off)
{
__u16 val;
/* copy 2 bytes from buffer, in memcpy order, */
/* handling possible wrap at end of buffer */
((__u8 *)&val)[0] = log->buffer[off];
if (likely(off+1 < log->size))
((__u8 *)&val)[1] = log->buffer[off+1];
else
((__u8 *)&val)[1] = log->buffer[0];
return sizeof(struct logger_entry) + val;
}
/*
* do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
* user-space buffer 'buf'. Returns 'count' on success.
*
* Caller must hold log->mutex.
*/
static ssize_t do_read_log_to_user(struct logger_log *log,
struct logger_reader *reader,
char __user *buf,
size_t count)
{
size_t len;
/*
* We read from the log in two disjoint operations. First, we read from
* the current read head offset up to 'count' bytes or to the end of
* the log, whichever comes first.
*/
len = min(count, log->size - reader->r_off);
if (copy_to_user(buf, log->buffer + reader->r_off, len))
return -EFAULT;
/*
* Second, we read any remaining bytes, starting back at the head of
* the log.
*/
if (count != len)
if (copy_to_user(buf + len, log->buffer, count - len))
return -EFAULT;
reader->r_off = logger_offset(log, reader->r_off + count);
return count;
}
/*
* logger_read - our log's read() method
*
* Behavior:
*
* - O_NONBLOCK works
* - If there are no log entries to read, blocks until log is written to
* - Atomically reads exactly one log entry
*
* Optimal read size is LOGGER_ENTRY_MAX_LEN. Will set errno to EINVAL if read
* buffer is insufficient to hold next entry.
*/
static ssize_t logger_read(struct file *file, char __user *buf,
size_t count, loff_t *pos)
{
struct logger_reader *reader = file->private_data;
struct logger_log *log = reader->log;
ssize_t ret;
DEFINE_WAIT(wait);
start:
while (1) {
mutex_lock(&log->mutex);
prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
ret = (log->w_off == reader->r_off);
mutex_unlock(&log->mutex);
if (!ret)
break;
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
break;
}
if (signal_pending(current)) {
ret = -EINTR;
break;
}
schedule();
}
finish_wait(&log->wq, &wait);
if (ret)
return ret;
mutex_lock(&log->mutex);
/* is there still something to read or did we race? */
if (unlikely(log->w_off == reader->r_off)) {
mutex_unlock(&log->mutex);
goto start;
}
/* get the size of the next entry */
ret = get_entry_len(log, reader->r_off);
if (count < ret) {
ret = -EINVAL;
goto out;
}
/* get exactly one entry from the log */
ret = do_read_log_to_user(log, reader, buf, ret);
out:
mutex_unlock(&log->mutex);
return ret;
}
/*
* get_next_entry - return the offset of the first valid entry at least 'len'
* bytes after 'off'.
*
* Caller must hold log->mutex.
*/
static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
{
size_t count = 0;
do {
size_t nr = get_entry_len(log, off);
off = logger_offset(log, off + nr);
count += nr;
} while (count < len);
return off;
}
/*
* is_between - is a < c < b, accounting for wrapping of a, b, and c
* positions in the buffer
*
* That is, if a<b, check for c between a and b
* and if a>b, check for c outside (not between) a and b
*
* |------- a xxxxxxxx b --------|
* c^
*
* |xxxxx b --------- a xxxxxxxxx|
* c^
* or c^
*/
static inline int is_between(size_t a, size_t b, size_t c)
{
if (a < b) {
/* is c between a and b? */
if (a < c && c <= b)
return 1;
} else {
/* is c outside of b through a? */
if (c <= b || a < c)
return 1;
}
return 0;
}
/*
* fix_up_readers - walk the list of all readers and "fix up" any who were
* lapped by the writer; also do the same for the default "start head".
* We do this by "pulling forward" the readers and start head to the first
* entry after the new write head.
*
* The caller needs to hold log->mutex.
*/
static void fix_up_readers(struct logger_log *log, size_t len)
{
size_t old = log->w_off;
size_t new = logger_offset(log, old + len);
struct logger_reader *reader;
if (is_between(old, new, log->head))
log->head = get_next_entry(log, log->head, len);
list_for_each_entry(reader, &log->readers, list)
if (is_between(old, new, reader->r_off))
reader->r_off = get_next_entry(log, reader->r_off, len);
}
/*
* do_write_log - writes 'len' bytes from 'buf' to 'log'
*
* The caller needs to hold log->mutex.
*/
static void do_write_log(struct logger_log *log, const void *buf, size_t count)
{
size_t len;
len = min(count, log->size - log->w_off);
memcpy(log->buffer + log->w_off, buf, len);
if (count != len)
memcpy(log->buffer, buf + len, count - len);
log->w_off = logger_offset(log, log->w_off + count);
}
/*
* do_write_log_user - writes 'len' bytes from the user-space buffer 'buf' to
* the log 'log'
*
* The caller needs to hold log->mutex.
*
* Returns 'count' on success, negative error code on failure.
*/
static ssize_t do_write_log_from_user(struct logger_log *log,
const void __user *buf, size_t count)
{
size_t len;
len = min(count, log->size - log->w_off);
if (len && copy_from_user(log->buffer + log->w_off, buf, len))
return -EFAULT;
if (count != len)
if (copy_from_user(log->buffer, buf + len, count - len))
/*
* Note that by not updating w_off, this abandons the
* portion of the new entry that *was* successfully
* copied, just above. This is intentional to avoid
* message corruption from missing fragments.
*/
return -EFAULT;
log->w_off = logger_offset(log, log->w_off + count);
return count;
}
/*
* logger_aio_write - our write method, implementing support for write(),
* writev(), and aio_write(). Writes are our fast path, and we try to optimize
* them above all else.
*/
static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t ppos)
{
struct logger_log *log = file_get_log(iocb->ki_filp);
size_t orig = log->w_off;
struct logger_entry header;
struct timespec now;
ssize_t ret = 0;
now = current_kernel_time();
header.pid = current->tgid;
header.tid = current->pid;
header.sec = now.tv_sec;
header.nsec = now.tv_nsec;
header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
/* null writes succeed, return zero */
if (unlikely(!header.len))
return 0;
mutex_lock(&log->mutex);
/*
* Fix up any readers, pulling them forward to the first readable
* entry after (what will be) the new write offset. We do this now
* because if we partially fail, we can end up with clobbered log
* entries that encroach on readable buffer.
*/
fix_up_readers(log, sizeof(struct logger_entry) + header.len);
do_write_log(log, &header, sizeof(struct logger_entry));
while (nr_segs-- > 0) {
size_t len;
ssize_t nr;
/* figure out how much of this vector we can keep */
len = min_t(size_t, iov->iov_len, header.len - ret);
/* write out this segment's payload */
nr = do_write_log_from_user(log, iov->iov_base, len);
if (unlikely(nr < 0)) {
log->w_off = orig;
mutex_unlock(&log->mutex);
return nr;
}
iov++;
ret += nr;
}
mutex_unlock(&log->mutex);
/* wake up any blocked readers */
wake_up_interruptible(&log->wq);
return ret;
}
static struct logger_log *get_log_from_minor(int minor)
{
struct logger_log *log;
list_for_each_entry(log, &log_list, logs)
if (log->misc.minor == minor)
return log;
return NULL;
}
/*
* logger_open - the log's open() file operation
*
* Note how near a no-op this is in the write-only case. Keep it that way!
*/
static int logger_open(struct inode *inode, struct file *file)
{
struct logger_log *log;
int ret;
ret = nonseekable_open(inode, file);
if (ret)
return ret;
log = get_log_from_minor(MINOR(inode->i_rdev));
if (!log)
return -ENODEV;
if (file->f_mode & FMODE_READ) {
struct logger_reader *reader;
reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
if (!reader)
return -ENOMEM;
reader->log = log;
INIT_LIST_HEAD(&reader->list);
mutex_lock(&log->mutex);
reader->r_off = log->head;
list_add_tail(&reader->list, &log->readers);
mutex_unlock(&log->mutex);
file->private_data = reader;
} else
file->private_data = log;
return 0;
}
/*
* logger_release - the log's release file operation
*
* Note this is a total no-op in the write-only case. Keep it that way!
*/
static int logger_release(struct inode *ignored, struct file *file)
{
if (file->f_mode & FMODE_READ) {
struct logger_reader *reader = file->private_data;
struct logger_log *log = reader->log;
mutex_lock(&log->mutex);
list_del(&reader->list);
mutex_unlock(&log->mutex);
kfree(reader);
}
return 0;
}
/*
* logger_poll - the log's poll file operation, for poll/select/epoll
*
* Note we always return POLLOUT, because you can always write() to the log.
* Note also that, strictly speaking, a return value of POLLIN does not
* guarantee that the log is readable without blocking, as there is a small
* chance that the writer can lap the reader in the interim between poll()
* returning and the read() request.
*/
static unsigned int logger_poll(struct file *file, poll_table *wait)
{
struct logger_reader *reader;
struct logger_log *log;
unsigned int ret = POLLOUT | POLLWRNORM;
if (!(file->f_mode & FMODE_READ))
return ret;
reader = file->private_data;
log = reader->log;
poll_wait(file, &log->wq, wait);
mutex_lock(&log->mutex);
if (log->w_off != reader->r_off)
ret |= POLLIN | POLLRDNORM;
mutex_unlock(&log->mutex);
return ret;
}
static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct logger_log *log = file_get_log(file);
struct logger_reader *reader;
long ret = -ENOTTY;
mutex_lock(&log->mutex);
switch (cmd) {
case LOGGER_GET_LOG_BUF_SIZE:
ret = log->size;
break;
case LOGGER_GET_LOG_LEN:
if (!(file->f_mode & FMODE_READ)) {
ret = -EBADF;
break;
}
reader = file->private_data;
if (log->w_off >= reader->r_off)
ret = log->w_off - reader->r_off;
else
ret = (log->size - reader->r_off) + log->w_off;
break;
case LOGGER_GET_NEXT_ENTRY_LEN:
if (!(file->f_mode & FMODE_READ)) {
ret = -EBADF;
break;
}
reader = file->private_data;
if (log->w_off != reader->r_off)
ret = get_entry_len(log, reader->r_off);
else
ret = 0;
break;
case LOGGER_FLUSH_LOG:
if (!(file->f_mode & FMODE_WRITE)) {
ret = -EBADF;
break;
}
list_for_each_entry(reader, &log->readers, list)
reader->r_off = log->w_off;
log->head = log->w_off;
ret = 0;
break;
}
mutex_unlock(&log->mutex);
return ret;
}
static const struct file_operations logger_fops = {
.owner = THIS_MODULE,
.read = logger_read,
.aio_write = logger_aio_write,
.poll = logger_poll,
.unlocked_ioctl = logger_ioctl,
.compat_ioctl = logger_ioctl,
.open = logger_open,
.release = logger_release,
};
/*
* Log size must be a power of two, greater than LOGGER_ENTRY_MAX_LEN,
* and less than LONG_MAX minus LOGGER_ENTRY_MAX_LEN.
*/
static int __init create_log(char *log_name, int size)
{
int ret = 0;
struct logger_log *log;
unsigned char *buffer;
buffer = vmalloc(size);
if (buffer == NULL)
return -ENOMEM;
log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
if (log == NULL) {
ret = -ENOMEM;
goto out_free_buffer;
}
log->buffer = buffer;
log->misc.minor = MISC_DYNAMIC_MINOR;
log->misc.name = kstrdup(log_name, GFP_KERNEL);
if (log->misc.name == NULL) {
ret = -ENOMEM;
goto out_free_log;
}
log->misc.fops = &logger_fops;
log->misc.parent = NULL;
init_waitqueue_head(&log->wq);
INIT_LIST_HEAD(&log->readers);
mutex_init(&log->mutex);
log->w_off = 0;
log->head = 0;
log->size = size;
INIT_LIST_HEAD(&log->logs);
list_add_tail(&log->logs, &log_list);
/* finally, initialize the misc device for this log */
ret = misc_register(&log->misc);
if (unlikely(ret)) {
pr_err("failed to register misc device for log '%s'!\n",
log->misc.name);
goto out_free_log;
}
pr_info("created %luK log '%s'\n",
(unsigned long) log->size >> 10, log->misc.name);
return 0;
out_free_log:
kfree(log);
out_free_buffer:
vfree(buffer);
return ret;
}
static int __init logger_init(void)
{
int ret;
ret = create_log(LOGGER_LOG_MAIN, 256*1024);
if (unlikely(ret))
goto out;
ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
if (unlikely(ret))
goto out;
ret = create_log(LOGGER_LOG_RADIO, 256*1024);
if (unlikely(ret))
goto out;
ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
if (unlikely(ret))
goto out;
out:
return ret;
}
device_initcall(logger_init);