--- /dev/null
+/*
+ * 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/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 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);
git://ftp.safe.ca / safe / jmp / linux-2.6 / commitdiff