Re: [PATCH v8 10/11] mtd: Support kmsg dumper based on pstore/blk

[WeiXiong Liao]

hi Kees Cook,

On 2020/5/12 äå1:12, Kees Cook wrote:
> [resend to proper CC list...]
> 
> On Tue, May 12, 2020 at 11:12:42AM +0800, WeiXiong Liao wrote:
>> hi Kees Cook,
>>
>> The off parameter on mtdpsore_block*() does not align to block size,
>> which makes some bugs. For example, a block contains 4 dmesg zones
>> and it's expected to erase this block when user remove all files on
>> these zones. However it work failed since it get wrongly zonenum from
>> misaligned off.
> 
> Ah, okay. I haven't touched any of this logic. Did something change in
> pstore/blk or /zone that I broke? Regardless, can you send a regular
> patch for what you have below and I'll fold it into the mtdpstore
> commit.
> 

I will send a patch later. Maybe it needs to be reviewed again by MTD
maintainers. And everything in pstore/blk and /zone are OK.

> Thanks!
> 
> -Kees
> 
>> On 2020/5/12 AM 7:32, Kees Cook wrote:
>>> From: WeiXiong Liao <liaoweixiong@xxxxxxxxxxxxxxxxx>
>>>
>>> This introduces mtdpstore, which is similar to mtdoops but more
>>> powerful. It uses pstore/blk, and aims to store panic and oops logs to
>>> a flash partition, where pstore can later read back and present as files
>>> in the mounted pstore filesystem.
>>>
>>> To make mtdpstore work, the "blkdev" of pstore/blk should be set
>>> as MTD device name or MTD device number. For more details, see
>>> Documentation/admin-guide/pstore-blk.rst
>>>
>>> This solves a number of issues:
>>> - Work duplication: both of pstore and mtdoops do the same job storing
>>>   panic/oops log. They have very similar logic, registering to kmsg
>>>   dumper and storing logs to several chunks one by one.
>>> - Layer violations: drivers should provides methods instead of polices.
>>>   MTD should provide read/write/erase operations, and allow a higher
>>>   level drivers to provide the chunk management, kmsg dump
>>>   configuration, etc.
>>> - Missing features: pstore provides many additional features, including
>>>   presenting the logs as files, logging dump time and count, and
>>>   supporting other frontends like pmsg, console, etc.
>>>
>>> Signed-off-by: WeiXiong Liao <liaoweixiong@xxxxxxxxxxxxxxxxx>
>>> Link: https://lore.kernel.org/r/1585126506-18635-12-git-send-email-liaoweixiong@xxxxxxxxxxxxxxxxx
>>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>>> ---
>>>  Documentation/admin-guide/pstore-blk.rst |   9 +-
>>>  drivers/mtd/Kconfig                      |  10 +
>>>  drivers/mtd/Makefile                     |   1 +
>>>  drivers/mtd/mtdpstore.c                  | 563 +++++++++++++++++++++++
>>>  4 files changed, 581 insertions(+), 2 deletions(-)
>>>  create mode 100644 drivers/mtd/mtdpstore.c
>>>
>>> diff --git a/Documentation/admin-guide/pstore-blk.rst b/Documentation/admin-guide/pstore-blk.rst
>>> index d45341e55e82..296d5027787a 100644
>>> --- a/Documentation/admin-guide/pstore-blk.rst
>>> +++ b/Documentation/admin-guide/pstore-blk.rst
>>> @@ -43,9 +43,9 @@ blkdev
>>>  ~~~~~~
>>>  
>>>  The block device to use. Most of the time, it is a partition of block device.
>>> -It's required for pstore/blk.
>>> +It's required for pstore/blk. It is also used for MTD device.
>>>  
>>> -It accepts the following variants:
>>> +It accepts the following variants for block device:
>>>  
>>>  1. <hex_major><hex_minor> device number in hexadecimal represents itself; no
>>>     leading 0x, for example b302.
>>> @@ -64,6 +64,11 @@ It accepts the following variants:
>>>     partition with a known unique id.
>>>  #. <major>:<minor> major and minor number of the device separated by a colon.
>>>  
>>> +It accepts the following variants for MTD device:
>>> +
>>> +1. <device name> MTD device name. "pstore" is recommended.
>>> +#. <device number> MTD device number.
>>> +
>>>  kmsg_size
>>>  ~~~~~~~~~
>>>  
>>> diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
>>> index 42d401ea60ee..6ddab796216d 100644
>>> --- a/drivers/mtd/Kconfig
>>> +++ b/drivers/mtd/Kconfig
>>> @@ -170,6 +170,16 @@ config MTD_OOPS
>>>  	  buffer in a flash partition where it can be read back at some
>>>  	  later point.
>>>  
>>> +config MTD_PSTORE
>>> +	tristate "Log panic/oops to an MTD buffer based on pstore"
>>> +	depends on PSTORE_BLK
>>> +	help
>>> +	  This enables panic and oops messages to be logged to a circular
>>> +	  buffer in a flash partition where it can be read back as files after
>>> +	  mounting pstore filesystem.
>>> +
>>> +	  If unsure, say N.
>>> +
>>>  config MTD_SWAP
>>>  	tristate "Swap on MTD device support"
>>>  	depends on MTD && SWAP
>>> diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
>>> index 56cc60ccc477..593d0593a038 100644
>>> --- a/drivers/mtd/Makefile
>>> +++ b/drivers/mtd/Makefile
>>> @@ -20,6 +20,7 @@ obj-$(CONFIG_RFD_FTL)		+= rfd_ftl.o
>>>  obj-$(CONFIG_SSFDC)		+= ssfdc.o
>>>  obj-$(CONFIG_SM_FTL)		+= sm_ftl.o
>>>  obj-$(CONFIG_MTD_OOPS)		+= mtdoops.o
>>> +obj-$(CONFIG_MTD_PSTORE)	+= mtdpstore.o
>>>  obj-$(CONFIG_MTD_SWAP)		+= mtdswap.o
>>>  
>>>  nftl-objs		:= nftlcore.o nftlmount.o
>>> diff --git a/drivers/mtd/mtdpstore.c b/drivers/mtd/mtdpstore.c
>>> new file mode 100644
>>> index 000000000000..06084eff1004
>>> --- /dev/null
>>> +++ b/drivers/mtd/mtdpstore.c
>>> @@ -0,0 +1,563 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#define dev_fmt(fmt) "mtdoops-pstore: " fmt
>>> +
>>> +#include <linux/kernel.h>
>>> +#include <linux/module.h>
>>> +#include <linux/pstore_blk.h>
>>> +#include <linux/mtd/mtd.h>
>>> +#include <linux/bitops.h>
>>> +
>>> +static struct mtdpstore_context {
>>> +	int index;
>>> +	struct pstore_blk_config info;
>>> +	struct pstore_device_info dev;
>>> +	struct mtd_info *mtd;
>>> +	unsigned long *rmmap;		/* removed bit map */
>>> +	unsigned long *usedmap;		/* used bit map */
>>> +	/*
>>> +	 * used for panic write
>>> +	 * As there are no block_isbad for panic case, we should keep this
>>> +	 * status before panic to ensure panic_write not failed.
>>> +	 */
>>> +	unsigned long *badmap;		/* bad block bit map */
>>> +} oops_cxt;
>>> +
>>> +static int mtdpstore_block_isbad(struct mtdpstore_context *cxt, loff_t off)
>>> +{
>>> +	int ret;
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 blknum = div_u64(off, mtd->erasesize);
>>
>> -       u64 blknum = div_u64(off, mtd->erasesize);
>> +       u64 blknum;
>> +
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       blknum = div_u64(off, mtd->erasesize);
>>
>>> +
>>> +	if (test_bit(blknum, cxt->badmap))
>>> +		return true;
>>> +	ret = mtd_block_isbad(mtd, off);
>>> +	if (ret < 0) {
>>> +		dev_err(&mtd->dev, "mtd_block_isbad failed, aborting\n");
>>> +		return ret;
>>> +	} else if (ret > 0) {
>>> +		set_bit(blknum, cxt->badmap);
>>> +		return true;
>>> +	}
>>> +	return false;
>>> +}
>>> +
>>> +static inline int mtdpstore_panic_block_isbad(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 blknum = div_u64(off, mtd->erasesize);
>>> +
>>
>> -       u64 blknum = div_u64(off, mtd->erasesize);
>> +       u64 blknum;
>>
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       blknum = div_u64(off, mtd->erasesize);
>>
>>> +	return test_bit(blknum, cxt->badmap);
>>> +}
>>> +
>>> +static inline void mtdpstore_mark_used(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +
>>> +	dev_dbg(&mtd->dev, "mark zone %llu used\n", zonenum);
>>> +	set_bit(zonenum, cxt->usedmap);
>>> +}
>>> +
>>> +static inline void mtdpstore_mark_unused(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +
>>> +	dev_dbg(&mtd->dev, "mark zone %llu unused\n", zonenum);
>>> +	clear_bit(zonenum, cxt->usedmap);
>>> +}
>>> +
>>> +static inline void mtdpstore_block_mark_unused(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +	u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>>> +
>>
>> -       u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>> -       u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>> +       u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
>> +       u64 zonenum;
>>
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       zonenum = div_u64(off, cxt->info.kmsg_size);
>>
>>> +	while (zonecnt > 0) {
>>> +		dev_dbg(&mtd->dev, "mark zone %llu unused\n", zonenum);
>>> +		clear_bit(zonenum, cxt->usedmap);
>>> +		zonenum++;
>>> +		zonecnt--;
>>> +	}
>>> +}
>>> +
>>> +static inline int mtdpstore_is_used(struct mtdpstore_context *cxt, loff_t off)
>>> +{
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +	u64 blknum = div_u64(off, cxt->mtd->erasesize);
>>> +
>>> +	if (test_bit(blknum, cxt->badmap))
>>> +		return true;
>>> +	return test_bit(zonenum, cxt->usedmap);
>>> +}
>>> +
>>> +static int mtdpstore_block_is_used(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +	u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>>> +
>>
>> -       u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>> -       u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>> +       struct mtd_info *mtd = cxt->mtd;
>> +       u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
>> +       u64 zonenum;
>>
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       zonenum = div_u64(off, cxt->info.kmsg_size);
>>
>>> +	while (zonecnt > 0) {
>>> +		if (test_bit(zonenum, cxt->usedmap))
>>> +			return true;
>>> +		zonenum++;
>>> +		zonecnt--;
>>> +	}
>>> +	return false;
>>> +}
>>> +
>>> +static int mtdpstore_is_empty(struct mtdpstore_context *cxt, char *buf,
>>> +		size_t size)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	size_t sz;
>>> +	int i;
>>> +
>>> +	sz = min_t(uint32_t, size, mtd->writesize / 4);
>>> +	for (i = 0; i < sz; i++) {
>>> +		if (buf[i] != (char)0xFF)
>>> +			return false;
>>> +	}
>>> +	return true;
>>> +}
>>> +
>>> +static void mtdpstore_mark_removed(struct mtdpstore_context *cxt, loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +
>>> +	dev_dbg(&mtd->dev, "mark zone %llu removed\n", zonenum);
>>> +	set_bit(zonenum, cxt->rmmap);
>>> +}
>>> +
>>> +static void mtdpstore_block_clear_removed(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +	u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>>> +
>>
>> -       u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>> -       u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>> +       struct mtd_info *mtd = cxt->mtd;
>> +       u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
>> +       u64 zonenum;
>>
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       zonenum = div_u64(off, cxt->info.kmsg_size);
>>
>>> +	while (zonecnt > 0) {
>>> +		clear_bit(zonenum, cxt->rmmap);
>>> +		zonenum++;
>>> +		zonecnt--;
>>> +	}
>>> +}
>>> +
>>> +static int mtdpstore_block_is_removed(struct mtdpstore_context *cxt,
>>> +		loff_t off)
>>> +{
>>> +	u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>>> +	u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>>> +
>>
>> -       u64 zonenum = div_u64(off, cxt->info.kmsg_size);
>> -       u32 zonecnt = cxt->mtd->erasesize / cxt->info.kmsg_size;
>> +       struct mtd_info *mtd = cxt->mtd;
>> +       u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
>> +       u64 zonenum;
>>
>> +       off = ALIGN_DOWN(off, mtd->erasesize);
>> +       zonenum = div_u64(off, cxt->info.kmsg_size);
>>
>>> +	while (zonecnt > 0) {
>>> +		if (test_bit(zonenum, cxt->rmmap))
>>> +			return true;
>>> +		zonenum++;
>>> +		zonecnt--;
>>> +	}
>>> +	return false;
>>> +}
>>> +
>>> +static int mtdpstore_erase_do(struct mtdpstore_context *cxt, loff_t off)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	struct erase_info erase;
>>> +	int ret;
>>> +
>>
>> 	 int ret;
>>
>> +       off = ALIGN_DOWN(off, cxt->mtd->erasesize);
>>         dev_dbg(&mtd->dev, "try to erase off 0x%llx\n", off);
>>
>>> +	dev_dbg(&mtd->dev, "try to erase off 0x%llx\n", off);
>>> +	erase.len = cxt->mtd->erasesize;
>>> +	erase.addr = off;
>>> +	ret = mtd_erase(cxt->mtd, &erase);
>>> +	if (!ret)
>>> +		mtdpstore_block_clear_removed(cxt, off);
>>> +	else
>>> +		dev_err(&mtd->dev, "erase of region [0x%llx, 0x%llx] on \"%s\" failed\n",
>>> +		       (unsigned long long)erase.addr,
>>> +		       (unsigned long long)erase.len, cxt->info.device);
>>> +	return ret;
>>> +}
>>> +
>>> +/*
>>> + * called while removing file
>>> + *
>>> + * Avoiding over erasing, do erase block only when the whole block is unused.
>>> + * If the block contains valid log, do erase lazily on flush_removed() when
>>> + * unregister.
>>> + */
>>> +static ssize_t mtdpstore_erase(size_t size, loff_t off)
>>> +{
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +
>>> +	if (mtdpstore_block_isbad(cxt, off))
>>> +		return -EIO;
>>> +
>>> +	mtdpstore_mark_unused(cxt, off);
>>> +
>>> +	/* If the block still has valid data, mtdpstore do erase lazily */
>>> +	if (likely(mtdpstore_block_is_used(cxt, off))) {
>>> +		mtdpstore_mark_removed(cxt, off);
>>> +		return 0;
>>> +	}
>>> +
>>> +	/* all zones are unused, erase it */
>>> +	off = ALIGN_DOWN(off, cxt->mtd->erasesize);
>>
>>         /* all zones are unused, erase it */
>> -       off = ALIGN_DOWN(off, cxt->mtd->erasesize);
>>         return mtdpstore_erase_do(cxt, off);
>>
>>> +	return mtdpstore_erase_do(cxt, off);
>>> +}
>>> +
>>> +/*
>>> + * What is security for mtdpstore?
>>> + * As there is no erase for panic case, we should ensure at least one zone
>>> + * is writable. Otherwise, panic write will fail.
>>> + * If zone is used, write operation will return -ENOMSG, which means that
>>> + * pstore/blk will try one by one until gets an empty zone. So, it is not
>>> + * needed to ensure the next zone is empty, but at least one.
>>> + */
>>> +static int mtdpstore_security(struct mtdpstore_context *cxt, loff_t off)
>>> +{
>>> +	int ret = 0, i;
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u32 zonenum = (u32)div_u64(off, cxt->info.kmsg_size);
>>> +	u32 zonecnt = (u32)div_u64(cxt->mtd->size, cxt->info.kmsg_size);
>>> +	u32 blkcnt = (u32)div_u64(cxt->mtd->size, cxt->mtd->erasesize);
>>> +	u32 erasesize = cxt->mtd->erasesize;
>>> +
>>> +	for (i = 0; i < zonecnt; i++) {
>>> +		u32 num = (zonenum + i) % zonecnt;
>>> +
>>> +		/* found empty zone */
>>> +		if (!test_bit(num, cxt->usedmap))
>>> +			return 0;
>>> +	}
>>> +
>>> +	/* If there is no any empty zone, we have no way but to do erase */
>>> +	off = ALIGN_DOWN(off, erasesize);
>>> +	while (blkcnt--) {
>>> +		div64_u64_rem(off + erasesize, cxt->mtd->size, (u64 *)&off);
>>> +
>>> +		if (mtdpstore_block_isbad(cxt, off))
>>> +			continue;
>>> +
>>> +		ret = mtdpstore_erase_do(cxt, off);
>>> +		if (!ret) {
>>> +			mtdpstore_block_mark_unused(cxt, off);
>>> +			break;
>>> +		}
>>> +	}
>>> +
>>> +	if (ret)
>>> +		dev_err(&mtd->dev, "all blocks bad!\n");
>>> +	dev_dbg(&mtd->dev, "end security\n");
>>> +	return ret;
>>> +}
>>> +
>>> +static ssize_t mtdpstore_write(const char *buf, size_t size, loff_t off)
>>> +{
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	size_t retlen;
>>> +	int ret;
>>> +
>>> +	if (mtdpstore_block_isbad(cxt, off))
>>> +		return -ENOMSG;
>>> +
>>> +	/* zone is used, please try next one */
>>> +	if (mtdpstore_is_used(cxt, off))
>>> +		return -ENOMSG;
>>> +
>>> +	dev_dbg(&mtd->dev, "try to write off 0x%llx size %zu\n", off, size);
>>> +	ret = mtd_write(cxt->mtd, off, size, &retlen, (u_char *)buf);
>>> +	if (ret < 0 || retlen != size) {
>>> +		dev_err(&mtd->dev, "write failure at %lld (%zu of %zu written), err %d\n",
>>> +				off, retlen, size, ret);
>>> +		return -EIO;
>>> +	}
>>> +	mtdpstore_mark_used(cxt, off);
>>> +
>>> +	mtdpstore_security(cxt, off);
>>> +	return retlen;
>>> +}
>>> +
>>> +static inline bool mtdpstore_is_io_error(int ret)
>>> +{
>>> +	return ret < 0 && !mtd_is_bitflip(ret) && !mtd_is_eccerr(ret);
>>> +}
>>> +
>>> +/*
>>> + * All zones will be read as pstore/blk will read zone one by one when do
>>> + * recover.
>>> + */
>>> +static ssize_t mtdpstore_read(char *buf, size_t size, loff_t off)
>>> +{
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	size_t retlen, done;
>>> +	int ret;
>>> +
>>> +	if (mtdpstore_block_isbad(cxt, off))
>>> +		return -ENOMSG;
>>> +
>>> +	dev_dbg(&mtd->dev, "try to read off 0x%llx size %zu\n", off, size);
>>> +	for (done = 0, retlen = 0; done < size; done += retlen) {
>>> +		retlen = 0;
>>> +
>>> +		ret = mtd_read(cxt->mtd, off + done, size - done, &retlen,
>>> +				(u_char *)buf + done);
>>> +		if (mtdpstore_is_io_error(ret)) {
>>> +			dev_err(&mtd->dev, "read failure at %lld (%zu of %zu read), err %d\n",
>>> +					off + done, retlen, size - done, ret);
>>> +			/* the zone may be broken, try next one */
>>> +			return -ENOMSG;
>>> +		}
>>> +
>>> +		/*
>>> +		 * ECC error. The impact on log data is so small. Maybe we can
>>> +		 * still read it and try to understand. So mtdpstore just hands
>>> +		 * over what it gets and user can judge whether the data is
>>> +		 * valid or not.
>>> +		 */
>>> +		if (mtd_is_eccerr(ret)) {
>>> +			dev_err(&mtd->dev, "ecc error at %lld (%zu of %zu read), err %d\n",
>>> +					off + done, retlen, size - done, ret);
>>> +			/* driver may not set retlen when ecc error */
>>> +			retlen = retlen == 0 ? size - done : retlen;
>>> +		}
>>> +	}
>>> +
>>> +	if (mtdpstore_is_empty(cxt, buf, size))
>>> +		mtdpstore_mark_unused(cxt, off);
>>> +	else
>>> +		mtdpstore_mark_used(cxt, off);
>>> +
>>> +	mtdpstore_security(cxt, off);
>>> +	return retlen;
>>> +}
>>> +
>>> +static ssize_t mtdpstore_panic_write(const char *buf, size_t size, loff_t off)
>>> +{
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	size_t retlen;
>>> +	int ret;
>>> +
>>> +	if (mtdpstore_panic_block_isbad(cxt, off))
>>> +		return -ENOMSG;
>>> +
>>> +	/* zone is used, please try next one */
>>> +	if (mtdpstore_is_used(cxt, off))
>>> +		return -ENOMSG;
>>> +
>>> +	ret = mtd_panic_write(cxt->mtd, off, size, &retlen, (u_char *)buf);
>>> +	if (ret < 0 || size != retlen) {
>>> +		dev_err(&mtd->dev, "panic write failure at %lld (%zu of %zu read), err %d\n",
>>> +				off, retlen, size, ret);
>>> +		return -EIO;
>>> +	}
>>> +	mtdpstore_mark_used(cxt, off);
>>> +
>>> +	return retlen;
>>> +}
>>> +
>>> +static void mtdpstore_notify_add(struct mtd_info *mtd)
>>> +{
>>> +	int ret;
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +	struct pstore_blk_config *info = &cxt->info;
>>> +	unsigned long longcnt;
>>> +
>>> +	if (!strcmp(mtd->name, info->device))
>>> +		cxt->index = mtd->index;
>>> +
>>> +	if (mtd->index != cxt->index || cxt->index < 0)
>>> +		return;
>>> +
>>> +	dev_dbg(&mtd->dev, "found matching MTD device %s\n", mtd->name);
>>> +
>>> +	if (mtd->size < info->kmsg_size * 2) {
>>> +		dev_err(&mtd->dev, "MTD partition %d not big enough\n",
>>> +				mtd->index);
>>> +		return;
>>> +	}
>>> +	/*
>>> +	 * kmsg_size must be aligned to 4096 Bytes, which is limited by
>>> +	 * psblk. The default value of kmsg_size is 64KB. If kmsg_size
>>> +	 * is larger than erasesize, some errors will occur since mtdpsotre
>>> +	 * is designed on it.
>>> +	 */
>>> +	if (mtd->erasesize < info->kmsg_size) {
>>> +		dev_err(&mtd->dev, "eraseblock size of MTD partition %d too small\n",
>>> +				mtd->index);
>>> +		return;
>>> +	}
>>> +	if (unlikely(info->kmsg_size % mtd->writesize)) {
>>> +		dev_err(&mtd->dev, "record size %lu KB must align to write size %d KB\n",
>>> +				info->kmsg_size / 1024,
>>> +				mtd->writesize / 1024);
>>> +		return;
>>> +	}
>>> +
>>> +	longcnt = BITS_TO_LONGS(div_u64(mtd->size, info->kmsg_size));
>>> +	cxt->rmmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +	cxt->usedmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +
>>> +	longcnt = BITS_TO_LONGS(div_u64(mtd->size, mtd->erasesize));
>>> +	cxt->badmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +
>>> +	cxt->dev.total_size = mtd->size;
>>> +	/* just support dmesg right now */
>>> +	cxt->dev.flags = PSTORE_FLAGS_DMESG;
>>> +	cxt->dev.read = mtdpstore_read;
>>> +	cxt->dev.write = mtdpstore_write;
>>> +	cxt->dev.erase = mtdpstore_erase;
>>> +	cxt->dev.panic_write = mtdpstore_panic_write;
>>> +
>>> +	ret = register_pstore_device(&cxt->dev);
>>> +	if (ret) {
>>> +		dev_err(&mtd->dev, "mtd%d register to psblk failed\n",
>>> +				mtd->index);
>>> +		return;
>>> +	}
>>> +	cxt->mtd = mtd;
>>> +	dev_info(&mtd->dev, "Attached to MTD device %d\n", mtd->index);
>>> +}
>>> +
>>> +static int mtdpstore_flush_removed_do(struct mtdpstore_context *cxt,
>>> +		loff_t off, size_t size)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	u_char *buf;
>>> +	int ret;
>>> +	size_t retlen;
>>> +	struct erase_info erase;
>>> +
>>> +	buf = kmalloc(mtd->erasesize, GFP_KERNEL);
>>> +	if (!buf)
>>> +		return -ENOMEM;
>>> +
>>> +	/* 1st. read to cache */
>>> +	ret = mtd_read(mtd, off, mtd->erasesize, &retlen, buf);
>>> +	if (mtdpstore_is_io_error(ret))
>>> +		goto free;
>>> +
>>> +	/* 2nd. erase block */
>>> +	erase.len = mtd->erasesize;
>>> +	erase.addr = off;
>>> +	ret = mtd_erase(mtd, &erase);
>>> +	if (ret)
>>> +		goto free;
>>> +
>>> +	/* 3rd. write back */
>>> +	while (size) {
>>> +		unsigned int zonesize = cxt->info.kmsg_size;
>>> +
>>> +		/* there is valid data on block, write back */
>>> +		if (mtdpstore_is_used(cxt, off)) {
>>> +			ret = mtd_write(mtd, off, zonesize, &retlen, buf);
>>> +			if (ret)
>>> +				dev_err(&mtd->dev, "write failure at %lld (%zu of %u written), err %d\n",
>>> +						off, retlen, zonesize, ret);
>>> +		}
>>> +
>>> +		off += zonesize;
>>> +		size -= min_t(unsigned int, zonesize, size);
>>> +	}
>>> +
>>> +free:
>>> +	kfree(buf);
>>> +	return ret;
>>> +}
>>> +
>>> +/*
>>> + * What does mtdpstore_flush_removed() do?
>>> + * When user remove any log file on pstore filesystem, mtdpstore should do
>>> + * something to ensure log file removed. If the whole block is no longer used,
>>> + * it's nice to erase the block. However if the block still contains valid log,
>>> + * what mtdpstore can do is to erase and write the valid log back.
>>> + */
>>> +static int mtdpstore_flush_removed(struct mtdpstore_context *cxt)
>>> +{
>>> +	struct mtd_info *mtd = cxt->mtd;
>>> +	int ret;
>>> +	loff_t off;
>>> +	u32 blkcnt = (u32)div_u64(mtd->size, mtd->erasesize);
>>> +
>>> +	for (off = 0; blkcnt > 0; blkcnt--, off += mtd->erasesize) {
>>> +		ret = mtdpstore_block_isbad(cxt, off);
>>> +		if (ret)
>>> +			continue;
>>> +
>>> +		ret = mtdpstore_block_is_removed(cxt, off);
>>> +		if (!ret)
>>> +			continue;
>>> +
>>> +		ret = mtdpstore_flush_removed_do(cxt, off, mtd->erasesize);
>>> +		if (ret)
>>> +			return ret;
>>> +	}
>>> +	return 0;
>>> +}
>>> +
>>> +static void mtdpstore_notify_remove(struct mtd_info *mtd)
>>> +{
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +
>>> +	if (mtd->index != cxt->index || cxt->index < 0)
>>> +		return;
>>> +
>>> +	mtdpstore_flush_removed(cxt);
>>> +
>>> +	unregister_pstore_device(&cxt->dev);
>>> +	kfree(cxt->badmap);
>>> +	kfree(cxt->usedmap);
>>> +	kfree(cxt->rmmap);
>>> +	cxt->mtd = NULL;
>>> +	cxt->index = -1;
>>> +}
>>> +
>>> +static struct mtd_notifier mtdpstore_notifier = {
>>> +	.add	= mtdpstore_notify_add,
>>> +	.remove	= mtdpstore_notify_remove,
>>> +};
>>> +
>>> +static int __init mtdpstore_init(void)
>>> +{
>>> +	int ret;
>>> +	struct mtdpstore_context *cxt = &oops_cxt;
>>> +	struct pstore_blk_config *info = &cxt->info;
>>> +
>>> +	ret = pstore_blk_get_config(info);
>>> +	if (unlikely(ret))
>>> +		return ret;
>>> +
>>> +	if (strlen(info->device) == 0) {
>>> +		pr_err("mtd device must be supplied (device name is empty)\n");
>>> +		return -EINVAL;
>>> +	}
>>> +	if (!info->kmsg_size) {
>>> +		pr_err("no backend enabled (kmsg_size is 0)\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	/* Setup the MTD device to use */
>>> +	ret = kstrtoint((char *)info->device, 0, &cxt->index);
>>> +	if (ret)
>>> +		cxt->index = -1;
>>> +
>>> +	register_mtd_user(&mtdpstore_notifier);
>>> +	return 0;
>>> +}
>>> +module_init(mtdpstore_init);
>>> +
>>> +static void __exit mtdpstore_exit(void)
>>> +{
>>> +	unregister_mtd_user(&mtdpstore_notifier);
>>> +}
>>> +module_exit(mtdpstore_exit);
>>> +
>>> +MODULE_LICENSE("GPL");
>>> +MODULE_AUTHOR("WeiXiong Liao <liaoweixiong@xxxxxxxxxxxxxxxxx>");
>>> +MODULE_DESCRIPTION("MTD backend for pstore/blk");
>>>
>>
>> -- 
>> WeiXiong Liao
> 

-- 
WeiXiong Liao