mtd: Support kmsg dumper based on pstore/blk

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@allwinnertech.com>
Link: https://lore.kernel.org/lkml/20200511233229.27745-11-keescook@chromium.org/
Link: https://lore.kernel.org/r/1589266715-4168-1-git-send-email-liaoweixiong@allwinnertech.com
Signed-off-by: Kees Cook <keescook@chromium.org>

4 files changed, 596 insertions, 2 deletions

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..a4fe6060b960
--- /dev/null
+++ b/drivers/mtd/mtdpstore.c
@@ -0,0 +1,578 @@
+// 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;
+
+	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;
+
+	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;
+	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)
+{
+	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)
+{
+	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)
+{
+	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;
+
+	off = ALIGN_DOWN(off, cxt->mtd->erasesize);
+	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 */
+	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 */
+	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@allwinnertech.com>");
+MODULE_DESCRIPTION("MTD backend for pstore/blk");