android logger: backport ANDROID_LOGGER driver

PD#131267: backport ANDROID_LOGGER driver
Android logger driver is legacy driver need by GC4A and low version
Android.

Change-Id: I16d305cd1b2c617a3515daafd5998210f2e21989
Signed-off-by: Frank Chen <frank.chen@amlogic.com>

MAINTAINERS

@@ -13662,3 +13662,8 @@ F: include/linux/amlogic/key_manage.h
 AMLOGIC P400 BSP
 M: Nan Li <frank.chen@amlogic.com>
 F: arch/arm64/boot/dts/amlogic/gxl_p400_2g.dts
+
+ANDROID LOGGER Driver
+M: Frank Chen <frank.chen@amlogic.com>
+F: drivers/staging/android/logger.c
+F: drivers/staging/android/logger.h

arch/arm64/configs/meson64_defconfig

@@ -320,6 +320,7 @@ CONFIG_UIO=y
 CONFIG_UIO_PDRV_GENIRQ=y
 CONFIG_VIRTIO_MMIO=y
 CONFIG_STAGING=y
+CONFIG_ANDROID_LOGGER=y
 CONFIG_PM_DEVFREQ=y
 CONFIG_DEVFREQ_GOV_SIMPLE_ONDEMAND=y
 CONFIG_DEVFREQ_GOV_PERFORMANCE=y

drivers/staging/android/Kconfig

@@ -14,6 +14,23 @@ config ASHMEM
 	  It is, in theory, a good memory allocator for low-memory devices,
 	  because it can discard shared memory units when under memory pressure.
 
+config ANDROID_LOGGER
+        tristate "Android log driver"
+        default n
+        ---help---
+          This adds support for system-wide logging using four log buffers.
+
+          These are:
+
+              1: main
+              2: events
+              3: radio
+              4: system
+
+          Log reading and writing is performed via normal Linux reads and
+          optimized writes. This optimization avoids logging having too
+          much overhead in the system.
+
 config ANDROID_LOW_MEMORY_KILLER
 	bool "Android Low Memory Killer"
 	---help---

drivers/staging/android/Makefile

@@ -4,4 +4,5 @@ obj-y					+= ion/
 obj-$(CONFIG_FIQ_DEBUGGER)		+= fiq_debugger/
 
 obj-$(CONFIG_ASHMEM)			+= ashmem.o
+obj-$(CONFIG_ANDROID_LOGGER)            += logger.o
 obj-$(CONFIG_ANDROID_LOW_MEMORY_KILLER)	+= lowmemorykiller.o

drivers/staging/android/logger.c

@@ -0,0 +1,808 @@
+/*
+ * 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 <linux/aio.h>
+#include <linux/uio.h>
+#include "logger.h"
+
+#include <asm/ioctls.h>
+
+/**
+ * struct logger_log - represents a specific log, such as 'main' or 'radio'
+ * @buffer:	The actual ring buffer
+ * @misc:	The "misc" device representing the log
+ * @wq:		The wait queue for @readers
+ * @readers:	This log's readers
+ * @mutex:	The mutex that protects the @buffer
+ * @w_off:	The current write head offset
+ * @head:	The head, or location that readers start reading at.
+ * @size:	The size of the log
+ * @logs:	The list of log channels
+ *
+ * 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;
+	struct miscdevice	misc;
+	wait_queue_head_t	wq;
+	struct list_head	readers;
+	struct mutex		mutex; /* log mutex */
+	size_t			w_off;
+	size_t			head;
+	size_t			size;
+	struct list_head	logs;
+};
+
+static LIST_HEAD(log_list);
+
+/**
+ * struct logger_reader - a logging device open for reading
+ * @log:	The associated log
+ * @list:	The associated entry in @logger_log's list
+ * @r_off:	The current read head offset.
+ * @r_all:	Reader can read all entries
+ * @r_ver:	Reader ABI version
+ *
+ * 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;
+	struct list_head	list;
+	size_t			r_off;
+	bool			r_all;
+	int			r_ver;
+};
+
+/* 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;
+	}
+	return file->private_data;
+}
+
+/*
+ * get_entry_header - returns a pointer to the logger_entry header within
+ * 'log' starting at offset 'off'. A temporary logger_entry 'scratch' must
+ * be provided. Typically the return value will be a pointer within
+ * 'logger->buf'.  However, a pointer to 'scratch' may be returned if
+ * the log entry spans the end and beginning of the circular buffer.
+ */
+static struct logger_entry *get_entry_header(struct logger_log *log,
+					     size_t off,
+					     struct logger_entry *scratch)
+{
+	size_t len = min(sizeof(struct logger_entry), log->size - off);
+
+	if (len != sizeof(struct logger_entry)) {
+		memcpy(((void *)scratch), log->buffer + off, len);
+		memcpy(((void *)scratch) + len, log->buffer,
+		       sizeof(struct logger_entry) - len);
+		return scratch;
+	}
+
+	return (struct logger_entry *)(log->buffer + off);
+}
+
+/*
+ * get_entry_msg_len - Grabs the length of the message of the entry
+ * starting from 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_msg_len(struct logger_log *log, size_t off)
+{
+	struct logger_entry scratch;
+	struct logger_entry *entry;
+
+	entry = get_entry_header(log, off, &scratch);
+	return entry->len;
+}
+
+static size_t get_user_hdr_len(int ver)
+{
+	if (ver < 2)
+		return sizeof(struct user_logger_entry_compat);
+	return sizeof(struct logger_entry);
+}
+
+static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
+				   char __user *buf)
+{
+	void *hdr;
+	size_t hdr_len;
+	struct user_logger_entry_compat v1;
+
+	if (ver < 2) {
+		v1.len      = entry->len;
+		v1.__pad    = 0;
+		v1.pid      = entry->pid;
+		v1.tid      = entry->tid;
+		v1.sec      = entry->sec;
+		v1.nsec     = entry->nsec;
+		hdr         = &v1;
+		hdr_len     = sizeof(struct user_logger_entry_compat);
+	} else {
+		hdr         = entry;
+		hdr_len     = sizeof(struct logger_entry);
+	}
+
+	return copy_to_user(buf, hdr, hdr_len);
+}
+
+/*
+ * 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)
+{
+	struct logger_entry scratch;
+	struct logger_entry *entry;
+	size_t len;
+	size_t msg_start;
+
+	/*
+	 * First, copy the header to userspace, using the version of
+	 * the header requested
+	 */
+	entry = get_entry_header(log, reader->r_off, &scratch);
+	if (copy_header_to_user(reader->r_ver, entry, buf))
+		return -EFAULT;
+
+	count -= get_user_hdr_len(reader->r_ver);
+	buf += get_user_hdr_len(reader->r_ver);
+	msg_start = logger_offset(log,
+				  reader->r_off + sizeof(struct logger_entry));
+
+	/*
+	 * We read from the msg in two disjoint operations. First, we read from
+	 * the current msg head offset up to 'count' bytes or to the end of
+	 * the log, whichever comes first.
+	 */
+	len = min(count, log->size - msg_start);
+	if (copy_to_user(buf, log->buffer + msg_start, 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 +
+		sizeof(struct logger_entry) + count);
+
+	return count + get_user_hdr_len(reader->r_ver);
+}
+
+/*
+ * get_next_entry_by_uid - Starting at 'off', returns an offset into
+ * 'log->buffer' which contains the first entry readable by 'euid'
+ */
+static size_t get_next_entry_by_uid(struct logger_log *log,
+				    size_t off, kuid_t euid)
+{
+	while (off != log->w_off) {
+		struct logger_entry *entry;
+		struct logger_entry scratch;
+		size_t next_len;
+
+		entry = get_entry_header(log, off, &scratch);
+
+		if (uid_eq(entry->euid, euid))
+			return off;
+
+		next_len = sizeof(struct logger_entry) + entry->len;
+		off = logger_offset(log, off + next_len);
+	}
+
+	return off;
+}
+
+/*
+ * 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
+ *
+ * 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);
+
+	if (!reader->r_all)
+		reader->r_off = get_next_entry_by_uid(log,
+			reader->r_off, current_euid());
+
+	/* 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_user_hdr_len(reader->r_ver) +
+		get_entry_msg_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 = sizeof(struct logger_entry) +
+			get_entry_msg_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);
+}
+
+/*
+ * logger_write_iter - 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_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct logger_log *log = file_get_log(iocb->ki_filp);
+	struct logger_entry header;
+	struct timespec now;
+	size_t len, count, w_off;
+
+	count = min_t(size_t, iov_iter_count(from), LOGGER_ENTRY_MAX_PAYLOAD);
+
+	now = current_kernel_time();
+
+	header.pid = current->tgid;
+	header.tid = current->pid;
+	header.sec = now.tv_sec;
+	header.nsec = now.tv_nsec;
+	header.euid = current_euid();
+	header.len = count;
+	header.hdr_size = sizeof(struct logger_entry);
+
+	/* 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);
+
+	len = min(sizeof(header), log->size - log->w_off);
+	memcpy(log->buffer + log->w_off, &header, len);
+	memcpy(log->buffer, (char *)&header + len, sizeof(header) - len);
+
+	/* Work with a copy until we are ready to commit the whole entry */
+	w_off =  logger_offset(log, log->w_off + sizeof(struct logger_entry));
+
+	len = min(count, log->size - w_off);
+
+	if (copy_from_iter(log->buffer + w_off, len, from) != len) {
+		/*
+		 * Note that by not updating log->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.
+		 */
+		mutex_unlock(&log->mutex);
+		return -EFAULT;
+	}
+
+	if (copy_from_iter(log->buffer, count - len, from) != count - len) {
+		mutex_unlock(&log->mutex);
+		return -EFAULT;
+	}
+
+	log->w_off = logger_offset(log, w_off + count);
+	mutex_unlock(&log->mutex);
+
+	/* wake up any blocked readers */
+	wake_up_interruptible(&log->wq);
+
+	return len;
+}
+
+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(*reader), GFP_KERNEL);
+		if (!reader)
+			return -ENOMEM;
+
+		reader->log = log;
+		reader->r_ver = 1;
+		reader->r_all = in_egroup_p(inode->i_gid) ||
+			capable(CAP_SYSLOG);
+
+		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 (!reader->r_all)
+		reader->r_off = get_next_entry_by_uid(log,
+			reader->r_off, current_euid());
+
+	if (log->w_off != reader->r_off)
+		ret |= POLLIN | POLLRDNORM;
+	mutex_unlock(&log->mutex);
+
+	return ret;
+}
+
+static long logger_set_version(struct logger_reader *reader, void __user *arg)
+{
+	int version;
+
+	if (copy_from_user(&version, arg, sizeof(int)))
+		return -EFAULT;
+
+	if ((version < 1) || (version > 2))
+		return -EINVAL;
+
+	reader->r_ver = version;
+	return 0;
+}
+
+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 = -EINVAL;
+	void __user *argp = (void __user *)arg;
+
+	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 (!reader->r_all)
+			reader->r_off = get_next_entry_by_uid(log,
+				reader->r_off, current_euid());
+
+		if (log->w_off != reader->r_off)
+			ret = get_user_hdr_len(reader->r_ver) +
+				get_entry_msg_len(log, reader->r_off);
+		else
+			ret = 0;
+		break;
+	case LOGGER_FLUSH_LOG:
+		if (!(file->f_mode & FMODE_WRITE)) {
+			ret = -EBADF;
+			break;
+		}
+		if (!(in_egroup_p(file_inode(file)->i_gid) ||
+		      capable(CAP_SYSLOG))) {
+			ret = -EPERM;
+			break;
+		}
+		list_for_each_entry(reader, &log->readers, list)
+			reader->r_off = log->w_off;
+		log->head = log->w_off;
+		ret = 0;
+		break;
+	case LOGGER_GET_VERSION:
+		if (!(file->f_mode & FMODE_READ)) {
+			ret = -EBADF;
+			break;
+		}
+		reader = file->private_data;
+		ret = reader->r_ver;
+		break;
+	case LOGGER_SET_VERSION:
+		if (!(file->f_mode & FMODE_READ)) {
+			ret = -EBADF;
+			break;
+		}
+		reader = file->private_data;
+		ret = logger_set_version(reader, argp);
+		break;
+	}
+
+	mutex_unlock(&log->mutex);
+
+	return ret;
+}
+
+static const struct file_operations logger_fops = {
+	.owner = THIS_MODULE,
+	.read = logger_read,
+	.write_iter = logger_write_iter,
+	.poll = logger_poll,
+	.unlocked_ioctl = logger_ioctl,
+	.compat_ioctl = logger_ioctl,
+	.open = logger_open,
+	.release = logger_release,
+};
+
+/*
+ * Log size must must be a power of two, and greater than
+ * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
+ */
+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)
+		return -ENOMEM;
+
+	log = kzalloc(sizeof(*log), GFP_KERNEL);
+	if (!log) {
+		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) {
+		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_misc_name;
+	}
+
+	pr_info("created %luK log '%s'\n",
+		(unsigned long)log->size >> 10, log->misc.name);
+
+	return 0;
+
+out_free_misc_name:
+	kfree(log->misc.name);
+
+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, 512 * 1024);
+	if (unlikely(ret))
+		goto out;
+
+	ret = create_log(LOGGER_LOG_EVENTS, 1 * 1024);
+	if (unlikely(ret))
+		goto out;
+
+	ret = create_log(LOGGER_LOG_RADIO, 1 * 1024);
+	if (unlikely(ret))
+		goto out;
+
+	ret = create_log(LOGGER_LOG_SYSTEM, 16 * 1024);
+	if (unlikely(ret))
+		goto out;
+
+out:
+	return ret;
+}
+
+static void __exit logger_exit(void)
+{
+	struct logger_log *current_log, *next_log;
+
+	list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
+		/* we have to delete all the entry inside log_list */
+		misc_deregister(&current_log->misc);
+		vfree(current_log->buffer);
+		kfree(current_log->misc.name);
+		list_del(&current_log->logs);
+		kfree(current_log);
+	}
+}
+
+device_initcall(logger_init);
+module_exit(logger_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Robert Love, <rlove@google.com>");
+MODULE_DESCRIPTION("Android Logger");

drivers/staging/android/logger.h

@@ -0,0 +1,90 @@
+/* include/linux/logger.h
+ *
+ * Copyright (C) 2007-2008 Google, Inc.
+ * Author: Robert Love <rlove@android.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.
+ *
+ */
+
+#ifndef _LINUX_LOGGER_H
+#define _LINUX_LOGGER_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+/**
+ * struct user_logger_entry_compat - defines a single entry that is given
+ * to a logger
+ * @len:	The length of the payload
+ * @__pad:	Two bytes of padding that appear to be required
+ * @pid:	The generating process' process ID
+ * @tid:	The generating process' thread ID
+ * @sec:	The number of seconds that have elapsed since the Epoch
+ * @nsec:	The number of nanoseconds that have elapsed since @sec
+ * @msg:	The message that is to be logged
+ *
+ * The userspace structure for version 1 of the logger_entry ABI.
+ * This structure is returned to userspace unless the caller requests
+ * an upgrade to a newer ABI version.
+ */
+struct user_logger_entry_compat {
+	__u16		len;
+	__u16		__pad;
+	__s32		pid;
+	__s32		tid;
+	__s32		sec;
+	__s32		nsec;
+	char		msg[0];
+};
+
+/**
+ * struct logger_entry - defines a single entry that is given to a logger
+ * @len:	The length of the payload
+ * @hdr_size:	sizeof(struct logger_entry_v2)
+ * @pid:	The generating process' process ID
+ * @tid:	The generating process' thread ID
+ * @sec:	The number of seconds that have elapsed since the Epoch
+ * @nsec:	The number of nanoseconds that have elapsed since @sec
+ * @euid:	Effective UID of logger
+ * @msg:	The message that is to be logged
+ *
+ * The structure for version 2 of the logger_entry ABI.
+ * This structure is returned to userspace if ioctl(LOGGER_SET_VERSION)
+ * is called with version >= 2
+ */
+struct logger_entry {
+	__u16		len;
+	__u16		hdr_size;
+	__s32		pid;
+	__s32		tid;
+	__s32		sec;
+	__s32		nsec;
+	kuid_t		euid;
+	char		msg[0];
+};
+
+#define LOGGER_LOG_RADIO	"log_radio"	/* radio-related messages */
+#define LOGGER_LOG_EVENTS	"log_events"	/* system/hardware events */
+#define LOGGER_LOG_SYSTEM	"log_system"	/* system/framework messages */
+#define LOGGER_LOG_MAIN		"log_main"	/* everything else */
+
+#define LOGGER_ENTRY_MAX_PAYLOAD	4076
+
+#define __LOGGERIO	0xAE
+
+#define LOGGER_GET_LOG_BUF_SIZE		_IO(__LOGGERIO, 1) /* size of log */
+#define LOGGER_GET_LOG_LEN		_IO(__LOGGERIO, 2) /* used log len */
+#define LOGGER_GET_NEXT_ENTRY_LEN	_IO(__LOGGERIO, 3) /* next entry len */
+#define LOGGER_FLUSH_LOG		_IO(__LOGGERIO, 4) /* flush log */
+#define LOGGER_GET_VERSION		_IO(__LOGGERIO, 5) /* abi version */
+#define LOGGER_SET_VERSION		_IO(__LOGGERIO, 6) /* abi version */
+
+#endif /* _LINUX_LOGGER_H */