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