| /* |
| * 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. |
| */ |
| |
| #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/time.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 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 */ |
| #define logger_offset(n) ((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'. |
| * |
| * Caller needs to hold log->mutex. |
| */ |
| static __u32 get_entry_len(struct logger_log *log, size_t off) |
| { |
| __u16 val; |
| |
| switch (log->size - off) { |
| case 1: |
| memcpy(&val, log->buffer + off, 1); |
| memcpy(((char *) &val) + 1, log->buffer, 1); |
| break; |
| default: |
| memcpy(&val, log->buffer + off, 2); |
| } |
| |
| 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(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) { |
| prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE); |
| |
| mutex_lock(&log->mutex); |
| 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(off + nr); |
| count += nr; |
| } while (count < len); |
| |
| return off; |
| } |
| |
| /* |
| * clock_interval - is a < c < b in mod-space? Put another way, does the line |
| * from a to b cross c? |
| */ |
| static inline int clock_interval(size_t a, size_t b, size_t c) |
| { |
| if (b < a) { |
| if (a < c || b >= c) |
| return 1; |
| } else { |
| if (a < c && b >= 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(old + len); |
| struct logger_reader *reader; |
| |
| if (clock_interval(old, new, log->head)) |
| log->head = get_next_entry(log, log->head, len); |
| |
| list_for_each_entry(reader, &log->readers, list) |
| if (clock_interval(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->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)) |
| return -EFAULT; |
| |
| log->w_off = logger_offset(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. |
| */ |
| 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); |
| |
| /* |
| * 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; |
| list_del(&reader->list); |
| 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, |
| }; |
| |
| /* |
| * Defines a log structure with name 'NAME' and a size of 'SIZE' bytes, which |
| * must be a power of two, greater than LOGGER_ENTRY_MAX_LEN, and less than |
| * LONG_MAX minus LOGGER_ENTRY_MAX_LEN. |
| */ |
| #define DEFINE_LOGGER_DEVICE(VAR, NAME, SIZE) \ |
| static unsigned char _buf_ ## VAR[SIZE]; \ |
| static struct logger_log VAR = { \ |
| .buffer = _buf_ ## VAR, \ |
| .misc = { \ |
| .minor = MISC_DYNAMIC_MINOR, \ |
| .name = NAME, \ |
| .fops = &logger_fops, \ |
| .parent = NULL, \ |
| }, \ |
| .wq = __WAIT_QUEUE_HEAD_INITIALIZER(VAR .wq), \ |
| .readers = LIST_HEAD_INIT(VAR .readers), \ |
| .mutex = __MUTEX_INITIALIZER(VAR .mutex), \ |
| .w_off = 0, \ |
| .head = 0, \ |
| .size = SIZE, \ |
| }; |
| |
| DEFINE_LOGGER_DEVICE(log_main, LOGGER_LOG_MAIN, 64*1024) |
| DEFINE_LOGGER_DEVICE(log_events, LOGGER_LOG_EVENTS, 256*1024) |
| DEFINE_LOGGER_DEVICE(log_radio, LOGGER_LOG_RADIO, 64*1024) |
| |
| static struct logger_log *get_log_from_minor(int minor) |
| { |
| if (log_main.misc.minor == minor) |
| return &log_main; |
| if (log_events.misc.minor == minor) |
| return &log_events; |
| if (log_radio.misc.minor == minor) |
| return &log_radio; |
| return NULL; |
| } |
| |
| static int __init init_log(struct logger_log *log) |
| { |
| int ret; |
| |
| ret = misc_register(&log->misc); |
| if (unlikely(ret)) { |
| printk(KERN_ERR "logger: failed to register misc " |
| "device for log '%s'!\n", log->misc.name); |
| return ret; |
| } |
| |
| printk(KERN_INFO "logger: created %luK log '%s'\n", |
| (unsigned long) log->size >> 10, log->misc.name); |
| |
| return 0; |
| } |
| |
| static int __init logger_init(void) |
| { |
| int ret; |
| |
| ret = init_log(&log_main); |
| if (unlikely(ret)) |
| goto out; |
| |
| ret = init_log(&log_events); |
| if (unlikely(ret)) |
| goto out; |
| |
| ret = init_log(&log_radio); |
| if (unlikely(ret)) |
| goto out; |
| |
| out: |
| return ret; |
| } |
| device_initcall(logger_init); |