drivers/mtd/mtdoops.c - kernel/windcharger - Git at Google

 /*
  * MTD Oops/Panic logger
  *
  * Copyright © 2007 Nokia Corporation. All rights reserved.
  *
  * Author: Richard Purdie <rpurdie@openedhand.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * version 2 as published by the Free Software Foundation.
  *
  * 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.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
  * 02110-1301 USA
  *
  */

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/console.h>
 #include <linux/vmalloc.h>
 #include <linux/workqueue.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/mtd/mtd.h>
 #include <linux/kmsg_dump.h>

 /* Maximum MTD partition size */
 #define MTDOOPS_MAX_MTD_SIZE (8 * 1024 * 1024)

 #define MTDOOPS_KERNMSG_MAGIC 0x5d005d00
 #define MTDOOPS_HEADER_SIZE   8

 static unsigned long record_size = 4096;
 module_param(record_size, ulong, 0400);
 MODULE_PARM_DESC(record_size,
 		"record size for MTD OOPS pages in bytes (default 4096)");

 static char mtddev[80];
 module_param_string(mtddev, mtddev, 80, 0400);
 MODULE_PARM_DESC(mtddev,
 		"name or index number of the MTD device to use");

 static int dump_oops = 1;
 module_param(dump_oops, int, 0600);
 MODULE_PARM_DESC(dump_oops,
 		"set to 1 to dump oopses, 0 to only dump panics (default 1)");

 static struct mtdoops_context {
 	struct kmsg_dumper dump;

 	int mtd_index;
 	struct work_struct work_erase;
 	struct work_struct work_write;
 	struct mtd_info *mtd;
 	int oops_pages;
 	int nextpage;
 	int nextcount;
 	unsigned long *oops_page_used;

 	void *oops_buf;
 } oops_cxt;

 static void mark_page_used(struct mtdoops_context *cxt, int page)
 {
 	set_bit(page, cxt->oops_page_used);
 }

 static void mark_page_unused(struct mtdoops_context *cxt, int page)
 {
 	clear_bit(page, cxt->oops_page_used);
 }

 static int page_is_used(struct mtdoops_context *cxt, int page)
 {
 	return test_bit(page, cxt->oops_page_used);
 }

 static void mtdoops_erase_callback(struct erase_info *done)
 {
 	wait_queue_head_t *wait_q = (wait_queue_head_t *)done->priv;
 	wake_up(wait_q);
 }

 static int mtdoops_erase_block(struct mtdoops_context *cxt, int offset)
 {
 	struct mtd_info *mtd = cxt->mtd;
 	u32 start_page_offset = mtd_div_by_eb(offset, mtd) * mtd->erasesize;
 	u32 start_page = start_page_offset / record_size;
 	u32 erase_pages = mtd->erasesize / record_size;
 	struct erase_info erase;
 	DECLARE_WAITQUEUE(wait, current);
 	wait_queue_head_t wait_q;
 	int ret;
 	int page;

 	init_waitqueue_head(&wait_q);
 	erase.mtd = mtd;
 	erase.callback = mtdoops_erase_callback;
 	erase.addr = offset;
 	erase.len = mtd->erasesize;
 	erase.priv = (u_long)&wait_q;

 	set_current_state(TASK_INTERRUPTIBLE);
 	add_wait_queue(&wait_q, &wait);

 	ret = mtd_erase(mtd, &erase);
 	if (ret) {
 		set_current_state(TASK_RUNNING);
 		remove_wait_queue(&wait_q, &wait);
 		printk(KERN_WARNING "mtdoops: erase of region [0x%llx, 0x%llx] on \"%s\" failed\n",
 		       (unsigned long long)erase.addr,
 		       (unsigned long long)erase.len, mtddev);
 		return ret;
 	}

 	schedule();  /* Wait for erase to finish. */
 	remove_wait_queue(&wait_q, &wait);

 	/* Mark pages as unused */
 	for (page = start_page; page < start_page + erase_pages; page++)
 		mark_page_unused(cxt, page);

 	return 0;
 }

 static void mtdoops_inc_counter(struct mtdoops_context *cxt)
 {
 	cxt->nextpage++;
 	if (cxt->nextpage >= cxt->oops_pages)
 		cxt->nextpage = 0;
 	cxt->nextcount++;
 	if (cxt->nextcount == 0xffffffff)
 		cxt->nextcount = 0;

 	if (page_is_used(cxt, cxt->nextpage)) {
 		schedule_work(&cxt->work_erase);
 		return;
 	}

 	printk(KERN_DEBUG "mtdoops: ready %d, %d (no erase)\n",
 	       cxt->nextpage, cxt->nextcount);
 }

 /* Scheduled work - when we can't proceed without erasing a block */
 static void mtdoops_workfunc_erase(struct work_struct *work)
 {
 	struct mtdoops_context *cxt =
 			container_of(work, struct mtdoops_context, work_erase);
 	struct mtd_info *mtd = cxt->mtd;
 	int i = 0, j, ret, mod;

 	/* We were unregistered */
 	if (!mtd)
 		return;

 	mod = (cxt->nextpage * record_size) % mtd->erasesize;
 	if (mod != 0) {
 		cxt->nextpage = cxt->nextpage + ((mtd->erasesize - mod) / record_size);
 		if (cxt->nextpage >= cxt->oops_pages)
 			cxt->nextpage = 0;
 	}

 	while (mtd_can_have_bb(mtd)) {
 		ret = mtd_block_isbad(mtd, cxt->nextpage * record_size);
 		if (!ret)
 			break;
 		if (ret < 0) {
 			printk(KERN_ERR "mtdoops: block_isbad failed, aborting\n");
 			return;
 		}
 badblock:
 		printk(KERN_WARNING "mtdoops: bad block at %08lx\n",
 		       cxt->nextpage * record_size);
 		i++;
 		cxt->nextpage = cxt->nextpage + (mtd->erasesize / record_size);
 		if (cxt->nextpage >= cxt->oops_pages)
 			cxt->nextpage = 0;
 		if (i == cxt->oops_pages / (mtd->erasesize / record_size)) {
 			printk(KERN_ERR "mtdoops: all blocks bad!\n");
 			return;
 		}
 	}

 	for (j = 0, ret = -1; (j < 3) && (ret < 0); j++)
 		ret = mtdoops_erase_block(cxt, cxt->nextpage * record_size);

 	if (ret >= 0) {
 		printk(KERN_DEBUG "mtdoops: ready %d, %d\n",
 		       cxt->nextpage, cxt->nextcount);
 		return;
 	}

 	if (mtd_can_have_bb(mtd) && ret == -EIO) {
 		ret = mtd_block_markbad(mtd, cxt->nextpage * record_size);
 		if (ret < 0) {
 			printk(KERN_ERR "mtdoops: block_markbad failed, aborting\n");
 			return;
 		}
 	}
 	goto badblock;
 }

 static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 {
 	struct mtd_info *mtd = cxt->mtd;
 	size_t retlen;
 	u32 *hdr;
 	int ret;

 	/* Add mtdoops header to the buffer */
 	hdr = cxt->oops_buf;
 	hdr[0] = cxt->nextcount;
 	hdr[1] = MTDOOPS_KERNMSG_MAGIC;

 	if (panic) {
 		ret = mtd_panic_write(mtd, cxt->nextpage * record_size,
 				      record_size, &retlen, cxt->oops_buf);
 		if (ret == -EOPNOTSUPP) {
 			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
 			return;
 		}
 	} else
 		ret = mtd_write(mtd, cxt->nextpage * record_size,
 				record_size, &retlen, cxt->oops_buf);

 	if (retlen != record_size || ret < 0)
 		printk(KERN_ERR "mtdoops: write failure at %ld (%td of %ld written), error %d\n",
 		       cxt->nextpage * record_size, retlen, record_size, ret);
 	mark_page_used(cxt, cxt->nextpage);
 	memset(cxt->oops_buf, 0xff, record_size);

 	mtdoops_inc_counter(cxt);
 }

 static void mtdoops_workfunc_write(struct work_struct *work)
 {
 	struct mtdoops_context *cxt =
 			container_of(work, struct mtdoops_context, work_write);

 	mtdoops_write(cxt, 0);
 }

 static void find_next_position(struct mtdoops_context *cxt)
 {
 	struct mtd_info *mtd = cxt->mtd;
 	int ret, page, maxpos = 0;
 	u32 count[2], maxcount = 0xffffffff;
 	size_t retlen;

 	for (page = 0; page < cxt->oops_pages; page++) {
 		if (mtd_can_have_bb(mtd) &&
 		    mtd_block_isbad(mtd, page * record_size))
 			continue;
 		/* Assume the page is used */
 		mark_page_used(cxt, page);
 		ret = mtd_read(mtd, page * record_size, MTDOOPS_HEADER_SIZE,
 			       &retlen, (u_char *)&count[0]);
 		if (retlen != MTDOOPS_HEADER_SIZE ||
 				(ret < 0 && !mtd_is_bitflip(ret))) {
 			printk(KERN_ERR "mtdoops: read failure at %ld (%td of %d read), err %d\n",
 			       page * record_size, retlen,
 			       MTDOOPS_HEADER_SIZE, ret);
 			continue;
 		}

 		if (count[0] == 0xffffffff && count[1] == 0xffffffff)
 			mark_page_unused(cxt, page);
 		if (count[0] == 0xffffffff)
 			continue;
 		if (maxcount == 0xffffffff) {
 			maxcount = count[0];
 			maxpos = page;
 		} else if (count[0] < 0x40000000 && maxcount > 0xc0000000) {
 			maxcount = count[0];
 			maxpos = page;
 		} else if (count[0] > maxcount && count[0] < 0xc0000000) {
 			maxcount = count[0];
 			maxpos = page;
 		} else if (count[0] > maxcount && count[0] > 0xc0000000
 					&& maxcount > 0x80000000) {
 			maxcount = count[0];
 			maxpos = page;
 		}
 	}
 	if (maxcount == 0xffffffff) {
 		cxt->nextpage = 0;
 		cxt->nextcount = 1;
 		schedule_work(&cxt->work_erase);
 		return;
 	}

 	cxt->nextpage = maxpos;
 	cxt->nextcount = maxcount;

 	mtdoops_inc_counter(cxt);
 }

 static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 			    enum kmsg_dump_reason reason)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);

 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;

 	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);

 	/* Panics must be written immediately */
 	if (reason != KMSG_DUMP_OOPS)
 		mtdoops_write(cxt, 1);

 	/* For other cases, schedule work to write it "nicely" */
 	schedule_work(&cxt->work_write);
 }

 static void mtdoops_notify_add(struct mtd_info *mtd)
 {
 	struct mtdoops_context *cxt = &oops_cxt;
 	u64 mtdoops_pages = div_u64(mtd->size, record_size);
 	int err;

 	if (!strcmp(mtd->name, mtddev))
 		cxt->mtd_index = mtd->index;

 	if (mtd->index != cxt->mtd_index || cxt->mtd_index < 0)
 		return;

 	if (mtd->size < mtd->erasesize * 2) {
 		printk(KERN_ERR "mtdoops: MTD partition %d not big enough for mtdoops\n",
 		       mtd->index);
 		return;
 	}
 	if (mtd->erasesize < record_size) {
 		printk(KERN_ERR "mtdoops: eraseblock size of MTD partition %d too small\n",
 		       mtd->index);
 		return;
 	}
 	if (mtd->size > MTDOOPS_MAX_MTD_SIZE) {
 		printk(KERN_ERR "mtdoops: mtd%d is too large (limit is %d MiB)\n",
 		       mtd->index, MTDOOPS_MAX_MTD_SIZE / 1024 / 1024);
 		return;
 	}

 	/* oops_page_used is a bit field */
 	cxt->oops_page_used = vmalloc(DIV_ROUND_UP(mtdoops_pages,
 			BITS_PER_LONG) * sizeof(unsigned long));
 	if (!cxt->oops_page_used) {
 		printk(KERN_ERR "mtdoops: could not allocate page array\n");
 		return;
 	}

 	cxt->dump.max_reason = KMSG_DUMP_OOPS;
 	cxt->dump.dump = mtdoops_do_dump;
 	err = kmsg_dump_register(&cxt->dump);
 	if (err) {
 		printk(KERN_ERR "mtdoops: registering kmsg dumper failed, error %d\n", err);
 		vfree(cxt->oops_page_used);
 		cxt->oops_page_used = NULL;
 		return;
 	}

 	cxt->mtd = mtd;
 	cxt->oops_pages = (int)mtd->size / record_size;
 	find_next_position(cxt);
 	printk(KERN_INFO "mtdoops: Attached to MTD device %d\n", mtd->index);
 }

 static void mtdoops_notify_remove(struct mtd_info *mtd)
 {
 	struct mtdoops_context *cxt = &oops_cxt;

 	if (mtd->index != cxt->mtd_index || cxt->mtd_index < 0)
 		return;

 	if (kmsg_dump_unregister(&cxt->dump) < 0)
 		printk(KERN_WARNING "mtdoops: could not unregister kmsg_dumper\n");

 	cxt->mtd = NULL;
 	flush_work_sync(&cxt->work_erase);
 	flush_work_sync(&cxt->work_write);
 }


 static struct mtd_notifier mtdoops_notifier = {
 	.add	= mtdoops_notify_add,
 	.remove	= mtdoops_notify_remove,
 };

 static int __init mtdoops_init(void)
 {
 	struct mtdoops_context *cxt = &oops_cxt;
 	int mtd_index;
 	char *endp;

 	if (strlen(mtddev) == 0) {
 		printk(KERN_ERR "mtdoops: mtd device (mtddev=name/number) must be supplied\n");
 		return -EINVAL;
 	}
 	if ((record_size & 4095) != 0) {
 		printk(KERN_ERR "mtdoops: record_size must be a multiple of 4096\n");
 		return -EINVAL;
 	}
 	if (record_size < 4096) {
 		printk(KERN_ERR "mtdoops: record_size must be over 4096 bytes\n");
 		return -EINVAL;
 	}

 	/* Setup the MTD device to use */
 	cxt->mtd_index = -1;
 	mtd_index = simple_strtoul(mtddev, &endp, 0);
 	if (*endp == '\0')
 		cxt->mtd_index = mtd_index;

 	cxt->oops_buf = vmalloc(record_size);
 	if (!cxt->oops_buf) {
 		printk(KERN_ERR "mtdoops: failed to allocate buffer workspace\n");
 		return -ENOMEM;
 	}
 	memset(cxt->oops_buf, 0xff, record_size);

 	INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase);
 	INIT_WORK(&cxt->work_write, mtdoops_workfunc_write);

 	register_mtd_user(&mtdoops_notifier);
 	return 0;
 }

 static void __exit mtdoops_exit(void)
 {
 	struct mtdoops_context *cxt = &oops_cxt;

 	unregister_mtd_user(&mtdoops_notifier);
 	vfree(cxt->oops_buf);
 	vfree(cxt->oops_page_used);
 }


 module_init(mtdoops_init);
 module_exit(mtdoops_exit);

 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Richard Purdie <rpurdie@openedhand.com>");
 MODULE_DESCRIPTION("MTD Oops/Panic console logger/driver");
	/*
	* MTD Oops/Panic logger
	*
	* Copyright © 2007 Nokia Corporation. All rights reserved.
	*
	* Author: Richard Purdie <rpurdie@openedhand.com>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* version 2 as published by the Free Software Foundation.
	*
	* 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.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
	* 02110-1301 USA
	*
	*/

	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/console.h>
	#include <linux/vmalloc.h>
	#include <linux/workqueue.h>
	#include <linux/sched.h>
	#include <linux/wait.h>
	#include <linux/delay.h>
	#include <linux/interrupt.h>
	#include <linux/mtd/mtd.h>
	#include <linux/kmsg_dump.h>

	/* Maximum MTD partition size */
	#define MTDOOPS_MAX_MTD_SIZE (8 * 1024 * 1024)

	#define MTDOOPS_KERNMSG_MAGIC 0x5d005d00
	#define MTDOOPS_HEADER_SIZE 8

	static unsigned long record_size = 4096;
	module_param(record_size, ulong, 0400);
	MODULE_PARM_DESC(record_size,
	"record size for MTD OOPS pages in bytes (default 4096)");

	static char mtddev[80];
	module_param_string(mtddev, mtddev, 80, 0400);
	MODULE_PARM_DESC(mtddev,
	"name or index number of the MTD device to use");

	static int dump_oops = 1;
	module_param(dump_oops, int, 0600);
	MODULE_PARM_DESC(dump_oops,
	"set to 1 to dump oopses, 0 to only dump panics (default 1)");

	static struct mtdoops_context {
	struct kmsg_dumper dump;

	int mtd_index;
	struct work_struct work_erase;
	struct work_struct work_write;
	struct mtd_info *mtd;
	int oops_pages;
	int nextpage;
	int nextcount;
	unsigned long *oops_page_used;

	void *oops_buf;
	} oops_cxt;

	static void mark_page_used(struct mtdoops_context *cxt, int page)
	{
	set_bit(page, cxt->oops_page_used);
	}

	static void mark_page_unused(struct mtdoops_context *cxt, int page)
	{
	clear_bit(page, cxt->oops_page_used);
	}

	static int page_is_used(struct mtdoops_context *cxt, int page)
	{
	return test_bit(page, cxt->oops_page_used);
	}

	static void mtdoops_erase_callback(struct erase_info *done)
	{
	wait_queue_head_t wait_q = (wait_queue_head_t )done->priv;
	wake_up(wait_q);
	}

	static int mtdoops_erase_block(struct mtdoops_context *cxt, int offset)
	{
	struct mtd_info *mtd = cxt->mtd;
	u32 start_page_offset = mtd_div_by_eb(offset, mtd) * mtd->erasesize;
	u32 start_page = start_page_offset / record_size;
	u32 erase_pages = mtd->erasesize / record_size;
	struct erase_info erase;
	DECLARE_WAITQUEUE(wait, current);
	wait_queue_head_t wait_q;
	int ret;
	int page;

	init_waitqueue_head(&wait_q);
	erase.mtd = mtd;
	erase.callback = mtdoops_erase_callback;
	erase.addr = offset;
	erase.len = mtd->erasesize;
	erase.priv = (u_long)&wait_q;

	set_current_state(TASK_INTERRUPTIBLE);
	add_wait_queue(&wait_q, &wait);

	ret = mtd_erase(mtd, &erase);
	if (ret) {
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&wait_q, &wait);
	printk(KERN_WARNING "mtdoops: erase of region [0x%llx, 0x%llx] on \"%s\" failed\n",
	(unsigned long long)erase.addr,
	(unsigned long long)erase.len, mtddev);
	return ret;
	}

	schedule(); /* Wait for erase to finish. */
	remove_wait_queue(&wait_q, &wait);

	/* Mark pages as unused */
	for (page = start_page; page < start_page + erase_pages; page++)
	mark_page_unused(cxt, page);

	return 0;
	}

	static void mtdoops_inc_counter(struct mtdoops_context *cxt)
	{
	cxt->nextpage++;
	if (cxt->nextpage >= cxt->oops_pages)
	cxt->nextpage = 0;
	cxt->nextcount++;
	if (cxt->nextcount == 0xffffffff)
	cxt->nextcount = 0;

	if (page_is_used(cxt, cxt->nextpage)) {
	schedule_work(&cxt->work_erase);
	return;
	}

	printk(KERN_DEBUG "mtdoops: ready %d, %d (no erase)\n",
	cxt->nextpage, cxt->nextcount);
	}

	/* Scheduled work - when we can't proceed without erasing a block */
	static void mtdoops_workfunc_erase(struct work_struct *work)
	{
	struct mtdoops_context *cxt =
	container_of(work, struct mtdoops_context, work_erase);
	struct mtd_info *mtd = cxt->mtd;
	int i = 0, j, ret, mod;

	/* We were unregistered */
	if (!mtd)
	return;

	mod = (cxt->nextpage * record_size) % mtd->erasesize;
	if (mod != 0) {
	cxt->nextpage = cxt->nextpage + ((mtd->erasesize - mod) / record_size);
	if (cxt->nextpage >= cxt->oops_pages)
	cxt->nextpage = 0;
	}

	while (mtd_can_have_bb(mtd)) {
	ret = mtd_block_isbad(mtd, cxt->nextpage * record_size);
	if (!ret)
	break;
	if (ret < 0) {
	printk(KERN_ERR "mtdoops: block_isbad failed, aborting\n");
	return;
	}
	badblock:
	printk(KERN_WARNING "mtdoops: bad block at %08lx\n",
	cxt->nextpage * record_size);
	i++;
	cxt->nextpage = cxt->nextpage + (mtd->erasesize / record_size);
	if (cxt->nextpage >= cxt->oops_pages)
	cxt->nextpage = 0;
	if (i == cxt->oops_pages / (mtd->erasesize / record_size)) {
	printk(KERN_ERR "mtdoops: all blocks bad!\n");
	return;
	}
	}

	for (j = 0, ret = -1; (j < 3) && (ret < 0); j++)
	ret = mtdoops_erase_block(cxt, cxt->nextpage * record_size);

	if (ret >= 0) {
	printk(KERN_DEBUG "mtdoops: ready %d, %d\n",
	cxt->nextpage, cxt->nextcount);
	return;
	}

	if (mtd_can_have_bb(mtd) && ret == -EIO) {
	ret = mtd_block_markbad(mtd, cxt->nextpage * record_size);
	if (ret < 0) {
	printk(KERN_ERR "mtdoops: block_markbad failed, aborting\n");
	return;
	}
	}
	goto badblock;
	}

	static void mtdoops_write(struct mtdoops_context *cxt, int panic)
	{
	struct mtd_info *mtd = cxt->mtd;
	size_t retlen;
	u32 *hdr;
	int ret;

	/* Add mtdoops header to the buffer */
	hdr = cxt->oops_buf;
	hdr[0] = cxt->nextcount;
	hdr[1] = MTDOOPS_KERNMSG_MAGIC;

	if (panic) {
	ret = mtd_panic_write(mtd, cxt->nextpage * record_size,
	record_size, &retlen, cxt->oops_buf);
	if (ret == -EOPNOTSUPP) {
	printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
	return;
	}
	} else
	ret = mtd_write(mtd, cxt->nextpage * record_size,
	record_size, &retlen, cxt->oops_buf);

	if (retlen != record_size \|\| ret < 0)
	printk(KERN_ERR "mtdoops: write failure at %ld (%td of %ld written), error %d\n",
	cxt->nextpage * record_size, retlen, record_size, ret);
	mark_page_used(cxt, cxt->nextpage);
	memset(cxt->oops_buf, 0xff, record_size);

	mtdoops_inc_counter(cxt);
	}

	static void mtdoops_workfunc_write(struct work_struct *work)
	{
	struct mtdoops_context *cxt =
	container_of(work, struct mtdoops_context, work_write);

	mtdoops_write(cxt, 0);
	}

	static void find_next_position(struct mtdoops_context *cxt)
	{
	struct mtd_info *mtd = cxt->mtd;
	int ret, page, maxpos = 0;
	u32 count[2], maxcount = 0xffffffff;
	size_t retlen;

	for (page = 0; page < cxt->oops_pages; page++) {
	if (mtd_can_have_bb(mtd) &&
	mtd_block_isbad(mtd, page * record_size))
	continue;
	/* Assume the page is used */
	mark_page_used(cxt, page);
	ret = mtd_read(mtd, page * record_size, MTDOOPS_HEADER_SIZE,
	&retlen, (u_char *)&count[0]);
	if (retlen != MTDOOPS_HEADER_SIZE \|\|
	(ret < 0 && !mtd_is_bitflip(ret))) {
	printk(KERN_ERR "mtdoops: read failure at %ld (%td of %d read), err %d\n",
	page * record_size, retlen,
	MTDOOPS_HEADER_SIZE, ret);
	continue;
	}

	if (count[0] == 0xffffffff && count[1] == 0xffffffff)
	mark_page_unused(cxt, page);
	if (count[0] == 0xffffffff)
	continue;
	if (maxcount == 0xffffffff) {
	maxcount = count[0];
	maxpos = page;
	} else if (count[0] < 0x40000000 && maxcount > 0xc0000000) {
	maxcount = count[0];
	maxpos = page;
	} else if (count[0] > maxcount && count[0] < 0xc0000000) {
	maxcount = count[0];
	maxpos = page;
	} else if (count[0] > maxcount && count[0] > 0xc0000000
	&& maxcount > 0x80000000) {
	maxcount = count[0];
	maxpos = page;
	}
	}
	if (maxcount == 0xffffffff) {
	cxt->nextpage = 0;
	cxt->nextcount = 1;
	schedule_work(&cxt->work_erase);
	return;
	}

	cxt->nextpage = maxpos;
	cxt->nextcount = maxcount;

	mtdoops_inc_counter(cxt);
	}

	static void mtdoops_do_dump(struct kmsg_dumper *dumper,
	enum kmsg_dump_reason reason)
	{
	struct mtdoops_context *cxt = container_of(dumper,
	struct mtdoops_context, dump);

	/* Only dump oopses if dump_oops is set */
	if (reason == KMSG_DUMP_OOPS && !dump_oops)
	return;

	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
	record_size - MTDOOPS_HEADER_SIZE, NULL);

	/* Panics must be written immediately */
	if (reason != KMSG_DUMP_OOPS)
	mtdoops_write(cxt, 1);

	/* For other cases, schedule work to write it "nicely" */
	schedule_work(&cxt->work_write);
	}

	static void mtdoops_notify_add(struct mtd_info *mtd)
	{
	struct mtdoops_context *cxt = &oops_cxt;
	u64 mtdoops_pages = div_u64(mtd->size, record_size);
	int err;

	if (!strcmp(mtd->name, mtddev))
	cxt->mtd_index = mtd->index;

	if (mtd->index != cxt->mtd_index \|\| cxt->mtd_index < 0)
	return;

	if (mtd->size < mtd->erasesize * 2) {
	printk(KERN_ERR "mtdoops: MTD partition %d not big enough for mtdoops\n",
	mtd->index);
	return;
	}
	if (mtd->erasesize < record_size) {
	printk(KERN_ERR "mtdoops: eraseblock size of MTD partition %d too small\n",
	mtd->index);
	return;
	}
	if (mtd->size > MTDOOPS_MAX_MTD_SIZE) {
	printk(KERN_ERR "mtdoops: mtd%d is too large (limit is %d MiB)\n",
	mtd->index, MTDOOPS_MAX_MTD_SIZE / 1024 / 1024);
	return;
	}

	/* oops_page_used is a bit field */
	cxt->oops_page_used = vmalloc(DIV_ROUND_UP(mtdoops_pages,
	BITS_PER_LONG) * sizeof(unsigned long));
	if (!cxt->oops_page_used) {
	printk(KERN_ERR "mtdoops: could not allocate page array\n");
	return;
	}

	cxt->dump.max_reason = KMSG_DUMP_OOPS;
	cxt->dump.dump = mtdoops_do_dump;
	err = kmsg_dump_register(&cxt->dump);
	if (err) {
	printk(KERN_ERR "mtdoops: registering kmsg dumper failed, error %d\n", err);
	vfree(cxt->oops_page_used);
	cxt->oops_page_used = NULL;
	return;
	}

	cxt->mtd = mtd;
	cxt->oops_pages = (int)mtd->size / record_size;
	find_next_position(cxt);
	printk(KERN_INFO "mtdoops: Attached to MTD device %d\n", mtd->index);
	}

	static void mtdoops_notify_remove(struct mtd_info *mtd)
	{
	struct mtdoops_context *cxt = &oops_cxt;

	if (mtd->index != cxt->mtd_index \|\| cxt->mtd_index < 0)
	return;

	if (kmsg_dump_unregister(&cxt->dump) < 0)
	printk(KERN_WARNING "mtdoops: could not unregister kmsg_dumper\n");

	cxt->mtd = NULL;
	flush_work_sync(&cxt->work_erase);
	flush_work_sync(&cxt->work_write);
	}


	static struct mtd_notifier mtdoops_notifier = {
	.add = mtdoops_notify_add,
	.remove = mtdoops_notify_remove,
	};

	static int __init mtdoops_init(void)
	{
	struct mtdoops_context *cxt = &oops_cxt;
	int mtd_index;
	char *endp;

	if (strlen(mtddev) == 0) {
	printk(KERN_ERR "mtdoops: mtd device (mtddev=name/number) must be supplied\n");
	return -EINVAL;
	}
	if ((record_size & 4095) != 0) {
	printk(KERN_ERR "mtdoops: record_size must be a multiple of 4096\n");
	return -EINVAL;
	}
	if (record_size < 4096) {
	printk(KERN_ERR "mtdoops: record_size must be over 4096 bytes\n");
	return -EINVAL;
	}

	/* Setup the MTD device to use */
	cxt->mtd_index = -1;
	mtd_index = simple_strtoul(mtddev, &endp, 0);
	if (*endp == '\0')
	cxt->mtd_index = mtd_index;

	cxt->oops_buf = vmalloc(record_size);
	if (!cxt->oops_buf) {
	printk(KERN_ERR "mtdoops: failed to allocate buffer workspace\n");
	return -ENOMEM;
	}
	memset(cxt->oops_buf, 0xff, record_size);

	INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase);
	INIT_WORK(&cxt->work_write, mtdoops_workfunc_write);

	register_mtd_user(&mtdoops_notifier);
	return 0;
	}

	static void __exit mtdoops_exit(void)
	{
	struct mtdoops_context *cxt = &oops_cxt;

	unregister_mtd_user(&mtdoops_notifier);
	vfree(cxt->oops_buf);
	vfree(cxt->oops_page_used);
	}


	module_init(mtdoops_init);
	module_exit(mtdoops_exit);

	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Richard Purdie <rpurdie@openedhand.com>");
	MODULE_DESCRIPTION("MTD Oops/Panic console logger/driver");