[RFC v4 1/3] pstore/rom: new support logger for block devices

[liaoweixiong]

pstore_rom is similar to pstore_ram, but dump log to block devices
rather than persistent ram.

Why should we need pstore_rom?
1. Most embedded intelligent equipment have no persistent ram, which
increases costs. We perfer to cheaper solutions, like block devices.
In fast, there is already a sample for block device logger in driver
MTD (drivers/mtd/mtdoops.c).
2. Do not any equipment have battery, which means that it lost all data
on general ram if power failure. Pstore has little to do for these
equipments.

pstore_rom can only dump Oops/Panic log to block devices. It only
supports dmesg now. To make pstore_rom work, the block driver should
provide the path of a block partition device (/dev/XXXX) and the
read/write apis when on panic.

pstore_rom begins at 'romz_register', by witch block device can register
a block partition to pstore_rom. Then pstore_rom divide and manage the
partition as zones, which is similar to pstore_ram.

Recommend that, block driver register pstore_rom after block device is
ready.

pstore_rom works well on allwinner(sunxi) platform.

Signed-off-by: liaoweixiong <liaoweixiong@xxxxxxxxxxxxxxxxx>
---
 fs/pstore/Kconfig          |   7 +
 fs/pstore/Makefile         |   3 +
 fs/pstore/romzone.c        | 961 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pstore_rom.h |  61 +++
 4 files changed, 1032 insertions(+)
 create mode 100644 fs/pstore/romzone.c
 create mode 100644 include/linux/pstore_rom.h

diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
index 8b3ba27..abf0453 100644
--- a/fs/pstore/Kconfig
+++ b/fs/pstore/Kconfig
@@ -152,3 +152,10 @@ config PSTORE_RAM
 	  "ramoops.ko".
 
 	  For more information, see Documentation/admin-guide/ramoops.rst.
+
+config PSTORE_ROM
+	tristate "Log panic/oops to a block device"
+	depends on PSTORE
+	help
+	  This enables panic and oops message to be logged to a block dev
+	  where it can be read back at some later point.
diff --git a/fs/pstore/Makefile b/fs/pstore/Makefile
index 967b589..ea38d6e 100644
--- a/fs/pstore/Makefile
+++ b/fs/pstore/Makefile
@@ -12,3 +12,6 @@ pstore-$(CONFIG_PSTORE_PMSG)	+= pmsg.o
 
 ramoops-objs += ram.o ram_core.o
 obj-$(CONFIG_PSTORE_RAM)	+= ramoops.o
+
+obj-$(CONFIG_PSTORE_ROM)	+= romoops.o
+romoops-y += romzone.o
diff --git a/fs/pstore/romzone.c b/fs/pstore/romzone.c
new file mode 100644
index 0000000..76a2648
--- /dev/null
+++ b/fs/pstore/romzone.c
@@ -0,0 +1,961 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *
+ * romzone.c: ROM Oops/Panic logger
+ *
+ * Copyright (C) 2019 liaoweixiong <liaoweixiong@xxxxxxxxxxxxxxxxxx>
+ *
+ * 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.
+ *
+ */
+
+#define pr_fmt(fmt) "romzone: " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/pstore.h>
+#include <linux/mount.h>
+#include <linux/pstore_rom.h>
+
+/**
+ * struct romz_head - head of zone to flush to storage
+ *
+ * @sig: signature to indicate header (ROM_SIG xor ROMZONE-type value)
+ * @datalen: length of data in @data
+ * @data: zone data.
+ */
+struct romz_buffer {
+#define ROM_SIG (0x43474244) /* DBGC */
+	uint32_t sig;
+	atomic_t datalen;
+	uint8_t data[0];
+};
+
+/**
+ * sruct romz_dmesg_header: dmesg information
+ *
+ * @magic: magic num for dmesg header
+ * @time: trigger time
+ * @compressed: whether conpressed
+ * @count: oops/panic counter
+ * @reason: identify oops or panic
+ */
+struct romz_dmesg_header {
+#define DMESG_HEADER_MAGIC 0x4dfc3ae5
+	uint32_t magic;
+	struct timespec64 time;
+	bool compressed;
+	uint32_t counter;
+	enum kmsg_dump_reason reason;
+	uint8_t data[0];
+};
+
+/**
+ * struct romz_zone - zone information
+ * @off:
+ *	zone offset of partition
+ * @type:
+ *	frontent type for this zone
+ * @name:
+ *	frontent name for this zone
+ * @buffer:
+ *	pointer to data buffer managed by this zone
+ * @buffer_size:
+ *	bytes in @buffer->data
+ * @should_recover:
+ *	should recover from storage
+ * @dirty:
+ *	mark whether the data in @buffer are dirty (not flush to storage yet)
+ */
+struct romz_zone {
+	unsigned long off;
+	const char *name;
+	enum pstore_type_id type;
+
+	struct romz_buffer *buffer;
+	size_t buffer_size;
+	bool should_recover;
+	atomic_t dirty;
+};
+
+struct romoops_context {
+	struct romz_zone **drzs;	/* Oops dump zones */
+	unsigned int dmesg_max_cnt;
+	unsigned int dmesg_read_cnt;
+	unsigned int dmesg_write_cnt;
+	/**
+	 * the counter should be recovered when do recovery
+	 * It records the oops/panic times after burning rather than booting.
+	 */
+	unsigned int oops_counter;
+	unsigned int panic_counter;
+	atomic_t blkdev_up;
+	atomic_t recovery;
+	atomic_t on_panic;
+
+	/*
+	 * rzinfo_lock just protects "rzinfo" during calls to
+	 * romz_register/romz_unregister
+	 */
+	spinlock_t rzinfo_lock;
+	struct romz_info *rzinfo;
+	struct pstore_info pstore;
+};
+static struct romoops_context romz_cxt;
+
+enum romz_flush_mode {
+	FLUSH_NONE = 0,
+	FLUSH_PART,
+	FLUSH_META,
+	FLUSH_ALL,
+};
+
+static inline int buffer_datalen(struct romz_zone *zone)
+{
+	return atomic_read(&zone->buffer->datalen);
+}
+
+static inline bool is_on_panic(void)
+{
+	struct romoops_context *cxt = &romz_cxt;
+
+	return atomic_read(&cxt->on_panic);
+}
+
+static inline bool is_blkdev_up(void)
+{
+	struct romoops_context *cxt = &romz_cxt;
+	const char *devpath = cxt->rzinfo->part_path;
+
+	if (atomic_read(&cxt->blkdev_up))
+		return true;
+	if (devpath && name_to_dev_t(devpath))
+		goto mark_blkdev_up;
+	if (is_on_panic())
+		goto mark_blkdev_up;
+
+	return false;
+mark_blkdev_up:
+	atomic_set(&cxt->blkdev_up, 1);
+	return true;
+}
+
+static int romz_zone_read(struct romz_zone *zone, char *buf,
+		size_t len, unsigned long off)
+{
+	if (!buf || !zone->buffer)
+		return -EINVAL;
+	len = min((size_t)len, (size_t)(zone->buffer_size - off));
+	memcpy(buf, zone->buffer->data + off, len);
+	return 0;
+}
+
+static int romz_zone_write(struct romz_zone *zone,
+		enum romz_flush_mode flush_mode, const char *buf,
+		size_t len, unsigned long off)
+{
+	struct romz_info *info = romz_cxt.rzinfo;
+	ssize_t wcnt;
+	ssize_t (*writeop)(const char *buf, size_t bytes, loff_t pos);
+	size_t wlen;
+
+	wlen = min((size_t)len, (size_t)(zone->buffer_size - off));
+	if (flush_mode != FLUSH_META && flush_mode != FLUSH_NONE) {
+		if (buf && zone->buffer)
+			memcpy(zone->buffer->data + off, buf, wlen);
+		atomic_set(&zone->buffer->datalen, wlen + off);
+	}
+
+	if (!is_blkdev_up())
+		goto set_dirty;
+
+	if (is_on_panic())
+		writeop = info->panic_write;
+	else
+		writeop = info->write;
+
+	switch (flush_mode) {
+	case FLUSH_NONE:
+		return 0;
+	case FLUSH_PART:
+		wcnt = writeop((const char *)zone->buffer->data + off, wlen,
+				zone->off + sizeof(*zone->buffer) + off);
+		if (wcnt != wlen)
+			goto set_dirty;
+	case FLUSH_META:
+		wlen = sizeof(struct romz_buffer);
+		wcnt = writeop((const char *)zone->buffer, wlen, zone->off);
+		if (wcnt != wlen)
+			goto set_dirty;
+		break;
+	case FLUSH_ALL:
+		wlen = buffer_datalen(zone) + sizeof(*zone->buffer);
+		wcnt = writeop((const char *)zone->buffer, wlen, zone->off);
+		if (wcnt != wlen)
+			goto set_dirty;
+		break;
+	}
+
+	return 0;
+set_dirty:
+	atomic_set(&zone->dirty, true);
+	return -EBUSY;
+}
+
+/*
+ * romz_move_zone: move data from a old zone to a new zone
+ *
+ * @old: the old zone
+ * @new: the new zone
+ *
+ * NOTE:
+ *	Call romz_zone_write to copy and flush data. If it failed, we
+ *	should reset new->dirty, because the new zone not realy dirty.
+ */
+static int romz_move_zone(struct romz_zone *old, struct romz_zone *new)
+{
+	const char *data = (const char *)old->buffer->data;
+	int ret;
+
+	ret = romz_zone_write(new, FLUSH_ALL, data, buffer_datalen(old), 0);
+	if (ret) {
+		atomic_set(&new->buffer->datalen, 0);
+		atomic_set(&new->dirty, false);
+		return ret;
+	}
+	atomic_set(&old->buffer->datalen, 0);
+	return 0;
+}
+
+static int romz_recover_dmesg_data(struct romoops_context *cxt)
+{
+	struct romz_info *info = cxt->rzinfo;
+	struct romz_zone *zone = NULL;
+	struct romz_buffer *buf;
+	unsigned long i;
+	ssize_t (*readop)(char *buf, size_t bytes, loff_t pos);
+	ssize_t rcnt;
+
+	readop = info->read;
+	if (is_on_panic())
+		readop = info->panic_read;
+	if (!readop)
+		return -EINVAL;
+
+	for (i = 0; i < cxt->dmesg_max_cnt; i++) {
+		zone = cxt->drzs[i];
+		if (!zone)
+			return -EINVAL;
+		if (atomic_read(&zone->dirty)) {
+			unsigned int wcnt = cxt->dmesg_write_cnt;
+			struct romz_zone *new = cxt->drzs[wcnt];
+			int ret;
+
+			ret = romz_move_zone(zone, new);
+			if (ret) {
+				pr_err("move zone from %lu to %d failed\n",
+						i, wcnt);
+				return ret;
+			}
+			cxt->dmesg_write_cnt = (wcnt + 1) % cxt->dmesg_max_cnt;
+		}
+		if (!zone->should_recover)
+			continue;
+		buf = zone->buffer;
+		rcnt = readop((char *)buf, zone->buffer_size + sizeof(*buf),
+				zone->off);
+		if (rcnt != zone->buffer_size + sizeof(*buf))
+			return rcnt;
+	}
+	return 0;
+}
+
+/*
+ * romz_recover_dmesg_meta: recover meta datas of dmesg
+ *
+ * Recover datas as follow:
+ * @cxt->dmesg_write_cnt
+ * @cxt->oops_counter
+ * @cxt->panic_counter
+ */
+static int romz_recover_dmesg_meta(struct romoops_context *cxt)
+{
+	unsigned long i;
+	struct romz_zone *zone;
+	size_t rcnt, len;
+	struct romz_buffer *buf;
+	struct romz_dmesg_header *hdr;
+	ssize_t (*readop)(char *buf, size_t bytes, loff_t pos);
+	int err = -EINVAL;
+	struct timespec64 time = {0};
+
+	readop = cxt->rzinfo->read;
+	if (is_on_panic())
+		readop = cxt->rzinfo->panic_read;
+	if (!readop)
+		return -EINVAL;
+
+	len = sizeof(*buf) + sizeof(*hdr);
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (i = 0; i < cxt->dmesg_max_cnt; i++) {
+		zone = cxt->drzs[i];
+		if (!zone)
+			goto free_buf;
+
+		rcnt = readop((char *)buf, len, zone->off);
+		if (rcnt != len)
+			goto free_buf;
+
+		/*
+		 * If sig NOT match, it means this zone never used before,
+		 * because we write one by one, and we never modify sig even
+		 * when erase. So, we do not need to check next one.
+		 */
+		if (buf->sig != zone->buffer->sig) {
+			cxt->dmesg_write_cnt = i;
+			pr_debug("no valid data in dmesg zone %lu\n", i);
+			break;
+		}
+
+		if (zone->buffer_size < atomic_read(&buf->datalen)) {
+			pr_info("found overtop zone: %s: id %lu, off %lu, size %zu\n",
+					zone->name, i, zone->off,
+					zone->buffer_size);
+			continue;
+		}
+
+		hdr = (struct romz_dmesg_header *)buf->data;
+		if (hdr->magic != DMESG_HEADER_MAGIC) {
+			pr_info("found invalid zone: %s: id %lu, off %lu, size %zu\n",
+					zone->name, i, zone->off,
+					zone->buffer_size);
+			continue;
+		}
+
+		/*
+		 * we get the newest zone, and the next one must be the oldest
+		 * or unused zone, because we do write one by one like a circle.
+		 */
+		if (hdr->time.tv_sec > time.tv_sec) {
+			time.tv_sec = hdr->time.tv_sec;
+			cxt->dmesg_write_cnt = (i + 1) % cxt->dmesg_max_cnt;
+		}
+
+		if (hdr->reason == KMSG_DUMP_OOPS)
+			cxt->oops_counter =
+				max(cxt->oops_counter, hdr->counter);
+		else
+			cxt->panic_counter =
+				max(cxt->panic_counter, hdr->counter);
+
+		if (!atomic_read(&buf->datalen)) {
+			pr_debug("found erased zone: %s: id %ld, off %lu, size %zu, datalen %d\n",
+					zone->name, i, zone->off,
+					zone->buffer_size,
+					atomic_read(&buf->datalen));
+			continue;
+		}
+
+		zone->should_recover = true;
+		pr_debug("found nice zone: %s: id %ld, off %lu, size %zu, datalen %d\n",
+				zone->name, i, zone->off,
+				zone->buffer_size, atomic_read(&buf->datalen));
+	}
+
+	err = 0;
+free_buf:
+	kfree(buf);
+	return err;
+}
+
+static int romz_recover_dmesg(struct romoops_context *cxt)
+{
+	int ret;
+
+	ret = romz_recover_dmesg_meta(cxt);
+	if (ret)
+		goto recover_fail;
+
+	ret = romz_recover_dmesg_data(cxt);
+	if (ret)
+		goto recover_fail;
+
+	return 0;
+recover_fail:
+	pr_debug("recovery dmesg failed\n");
+	return ret;
+}
+
+static inline int romz_recovery(struct romoops_context *cxt)
+{
+	int ret = -EBUSY;
+
+	if (atomic_read(&cxt->recovery))
+		return 0;
+
+	if (!is_blkdev_up())
+		goto recover_fail;
+
+	ret = romz_recover_dmesg(cxt);
+	if (ret)
+		goto recover_fail;
+
+	atomic_set(&cxt->recovery, 1);
+	pr_debug("recover end!\n");
+	return 0;
+
+recover_fail:
+	pr_debug("recovery failed, handle buffer\n");
+	return ret;
+}
+
+static int romoops_pstore_open(struct pstore_info *psi)
+{
+	struct romoops_context *cxt = psi->data;
+
+	cxt->dmesg_read_cnt = 0;
+	return 0;
+}
+
+static int romoops_pstore_erase(struct pstore_record *record)
+{
+	struct romoops_context *cxt = record->psi->data;
+	struct romz_zone *zone;
+
+	/*
+	 * before read/erase, we must recover from storage.
+	 * if recover failed, handle buffer
+	 */
+	romz_recovery(cxt);
+
+	if (record->type != PSTORE_TYPE_DMESG)
+		return -EINVAL;
+
+	zone = cxt->drzs[record->id];
+	if (!zone)
+		return -EINVAL;
+
+	if (!buffer_datalen(zone))
+		return 0;
+
+	atomic_set(&zone->buffer->datalen, 0);
+	return romz_zone_write(zone, FLUSH_META, NULL, 0, 0);
+}
+
+static void romoops_write_kmsg_hdr(struct romz_zone *zone,
+		struct pstore_record *record)
+{
+	struct romoops_context *cxt = record->psi->data;
+	struct romz_buffer *buffer = zone->buffer;
+	struct romz_dmesg_header *hdr =
+		(struct romz_dmesg_header *)buffer->data;
+
+	hdr->magic = DMESG_HEADER_MAGIC;
+	hdr->compressed = record->compressed;
+	hdr->time.tv_sec = record->time.tv_sec;
+	hdr->time.tv_nsec = record->time.tv_nsec;
+	hdr->reason = record->reason;
+	if (hdr->reason == KMSG_DUMP_OOPS)
+		hdr->counter = ++cxt->oops_counter;
+	else
+		hdr->counter = ++cxt->panic_counter;
+}
+
+static int notrace romz_dmesg_write(struct romoops_context *cxt,
+		struct pstore_record *record)
+{
+	struct romz_info *info = cxt->rzinfo;
+	struct romz_zone *zone;
+	size_t size, hlen;
+
+	/*
+	 * Out of the various dmesg dump types, ramoops is currently designed
+	 * to only store crash logs, rather than storing general kernel logs.
+	 */
+	if (record->reason != KMSG_DUMP_OOPS &&
+			record->reason != KMSG_DUMP_PANIC)
+		return -EINVAL;
+
+	/* Skip Oopes when configured to do so. */
+	if (record->reason == KMSG_DUMP_OOPS && !info->dump_oops)
+		return -EINVAL;
+
+	/*
+	 * Explicitly only take the first part of any new crash.
+	 * If our buffer is larger than kmsg_bytes, this can never happen,
+	 * and if our buffer is smaller than kmsg_bytes, we don't want the
+	 * report split across multiple records.
+	 */
+	if (record->part != 1)
+		return -ENOSPC;
+
+	if (!cxt->drzs)
+		return -ENOSPC;
+
+	zone = cxt->drzs[cxt->dmesg_write_cnt];
+	if (!zone)
+		return -ENOSPC;
+
+	romoops_write_kmsg_hdr(zone, record);
+	hlen = sizeof(struct romz_dmesg_header);
+	size = record->size;
+	if (size + hlen > zone->buffer_size)
+		size = zone->buffer_size - hlen;
+	romz_zone_write(zone, FLUSH_ALL, record->buf, size, hlen);
+
+	pr_debug("write %s to zone id %d\n", zone->name, cxt->dmesg_write_cnt);
+	cxt->dmesg_write_cnt = (cxt->dmesg_write_cnt + 1) % cxt->dmesg_max_cnt;
+	return 0;
+}
+
+static int notrace romoops_pstore_write(struct pstore_record *record)
+{
+	struct romoops_context *cxt = record->psi->data;
+
+	if (record->type == PSTORE_TYPE_DMESG &&
+			record->reason == KMSG_DUMP_PANIC)
+		atomic_set(&cxt->on_panic, 1);
+
+	/*
+	 * before read/erase, we must recover from storage.
+	 * if recover failed, handle buffer
+	 */
+	romz_recovery(cxt);
+
+	switch (record->type) {
+	case PSTORE_TYPE_DMESG:
+		return romz_dmesg_write(cxt, record);
+	default:
+		return -EINVAL;
+	}
+}
+
+static inline bool romz_ok(struct romz_zone *zone)
+{
+	if (!zone || !zone->buffer || !buffer_datalen(zone))
+		return false;
+	return true;
+}
+
+#define READ_NEXT_ZONE ((ssize_t)(-1024))
+static struct romz_zone *romz_read_next_zone(struct romoops_context *cxt)
+{
+	struct romz_zone *zone = NULL;
+
+	while (cxt->dmesg_read_cnt < cxt->dmesg_max_cnt) {
+		zone = cxt->drzs[cxt->dmesg_read_cnt++];
+		if (romz_ok(zone))
+			return zone;
+	}
+
+	return NULL;
+}
+
+static int romoops_read_dmesg_hdr(struct romz_zone *zone,
+		struct pstore_record *record)
+{
+	struct romz_buffer *buffer = zone->buffer;
+	struct romz_dmesg_header *hdr =
+		(struct romz_dmesg_header *)buffer->data;
+
+	if (hdr->magic != DMESG_HEADER_MAGIC)
+		return -EINVAL;
+	record->compressed = hdr->compressed;
+	record->time.tv_sec = hdr->time.tv_sec;
+	record->time.tv_nsec = hdr->time.tv_nsec;
+	record->reason = hdr->reason;
+	record->count = hdr->counter;
+	return 0;
+}
+
+static ssize_t romz_dmesg_read(struct romz_zone *zone,
+		struct pstore_record *record)
+{
+	size_t size, hlen = 0;
+
+	size = buffer_datalen(zone);
+	/* Clear and skip this DMESG record if it has no valid header */
+	if (romoops_read_dmesg_hdr(zone, record)) {
+		atomic_set(&zone->buffer->datalen, 0);
+		atomic_set(&zone->dirty, 0);
+		return READ_NEXT_ZONE;
+	}
+	size -= sizeof(struct romz_dmesg_header);
+
+	if (!record->compressed) {
+		char *buf = kasprintf(GFP_KERNEL,
+				"romoops: %s: Total %d times\n",
+				record->reason == KMSG_DUMP_OOPS ? "Oops" :
+				"Panic", record->count);
+		hlen = strlen(buf);
+		record->buf = krealloc(buf, hlen + size, GFP_KERNEL);
+		if (!record->buf) {
+			kfree(buf);
+			return -ENOMEM;
+		}
+	} else {
+		record->buf = kmalloc(size, GFP_KERNEL);
+		if (!record->buf)
+			return -ENOMEM;
+	}
+
+	if (unlikely(romz_zone_read(zone, record->buf + hlen, size,
+				sizeof(struct romz_dmesg_header)) < 0)) {
+		kfree(record->buf);
+		return READ_NEXT_ZONE;
+	}
+
+	return size + hlen;
+}
+
+static ssize_t romoops_pstore_read(struct pstore_record *record)
+{
+	struct romoops_context *cxt = record->psi->data;
+	ssize_t (*romz_read)(struct romz_zone *zone,
+			struct pstore_record *record);
+	struct romz_zone *zone;
+	ssize_t ret;
+
+	/*
+	 * before read/erase, we must recover from storage.
+	 * if recover failed, handle buffer
+	 */
+	romz_recovery(cxt);
+
+next_zone:
+	zone = romz_read_next_zone(cxt);
+	if (!zone)
+		return 0;
+
+	record->id = 0;
+	record->type = zone->type;
+
+	record->time.tv_sec = 0;
+	record->time.tv_nsec = 0;
+	record->compressed = false;
+
+	switch (record->type) {
+	case PSTORE_TYPE_DMESG:
+		romz_read = romz_dmesg_read;
+		record->id = cxt->dmesg_read_cnt - 1;
+		break;
+	default:
+		goto next_zone;
+	}
+
+	ret = romz_read(zone, record);
+	if (ret == READ_NEXT_ZONE)
+		goto next_zone;
+	return ret;
+}
+
+static struct romoops_context romz_cxt = {
+	.rzinfo_lock =  __SPIN_LOCK_UNLOCKED(romz_cxt.rzinfo_lock),
+	.blkdev_up = ATOMIC_INIT(0),
+	.recovery = ATOMIC_INIT(0),
+	.on_panic = ATOMIC_INIT(0),
+	.pstore = {
+		.owner = THIS_MODULE,
+		.name = "romoops",
+		.open = romoops_pstore_open,
+		.read = romoops_pstore_read,
+		.write = romoops_pstore_write,
+		.erase = romoops_pstore_erase,
+	},
+};
+
+static ssize_t romz_sample_read(char *buf, size_t bytes, loff_t pos)
+{
+	struct romoops_context *cxt = &romz_cxt;
+	const char *devpath = cxt->rzinfo->part_path;
+	struct file *filp;
+	ssize_t ret;
+
+	if (!is_blkdev_up())
+		return -EBUSY;
+
+	filp = filp_open(devpath, O_RDONLY, 0);
+	if (IS_ERR(filp)) {
+		pr_debug("open %s failed, maybe unready\n", devpath);
+		return -EACCES;
+	}
+	ret = kernel_read(filp, buf, bytes, &pos);
+	filp_close(filp, NULL);
+
+	return ret;
+}
+
+static ssize_t romz_sample_write(const char *buf, size_t bytes, loff_t pos)
+{
+	struct romoops_context *cxt = &romz_cxt;
+	const char *devpath = cxt->rzinfo->part_path;
+	struct file *filp;
+	ssize_t ret;
+
+	if (!is_blkdev_up())
+		return -EBUSY;
+
+	filp = filp_open(devpath, O_WRONLY, 0);
+	if (IS_ERR(filp)) {
+		pr_debug("open %s failed, maybe unready\n", devpath);
+		return -EACCES;
+	}
+	ret = kernel_write(filp, buf, bytes, &pos);
+	vfs_fsync(filp, 0);
+	filp_close(filp, NULL);
+
+	return ret;
+}
+
+static struct romz_zone *romz_init_zone(enum pstore_type_id type,
+		unsigned long *off, size_t size)
+{
+	struct romz_info *info = romz_cxt.rzinfo;
+	struct romz_zone *zone;
+	const char *name = pstore_type_to_name(type);
+
+	if (!size)
+		return NULL;
+
+	if (*off + size > info->part_size) {
+		pr_err("no room for %s (0x%zx@0x%lx over 0x%lx)\n",
+			name, size, *off, info->part_size);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	zone = kzalloc(sizeof(struct romz_zone), GFP_KERNEL);
+	if (!zone)
+		return ERR_PTR(-ENOMEM);
+
+	/**
+	 * NOTE: allocate buffer for rom zones for two reasons:
+	 * 1. It can temporarily hold the data before sample_read/write
+	 *    are useable.
+	 * 2. It makes pstore usable even if no persistent storage. Most
+	 *    events of pstore except panic are suitable!!
+	 */
+	zone->buffer = kmalloc(size, GFP_KERNEL);
+	if (!zone->buffer) {
+		kfree(zone);
+		return ERR_PTR(-ENOMEM);
+	}
+	memset(zone->buffer, 0xFF, size);
+	zone->off = *off;
+	zone->name = name;
+	zone->type = type;
+	zone->buffer_size = size - sizeof(struct romz_buffer);
+	zone->buffer->sig = type ^ ROM_SIG;
+	atomic_set(&zone->dirty, 0);
+	atomic_set(&zone->buffer->datalen, 0);
+
+	*off += size;
+
+	pr_debug("romzone %s: off 0x%lx, %zu header, %zu data\n", zone->name,
+			zone->off, sizeof(*zone->buffer), zone->buffer_size);
+	return zone;
+}
+
+static struct romz_zone **romz_init_zones(enum pstore_type_id type,
+	unsigned long *off, size_t total_size, ssize_t record_size,
+	unsigned int *cnt)
+{
+	struct romz_info *info = romz_cxt.rzinfo;
+	struct romz_zone **zones, *zone;
+	const char *name = pstore_type_to_name(type);
+	int c, i;
+
+	if (!total_size || !record_size)
+		return NULL;
+
+	if (*off + total_size > info->part_size) {
+		pr_err("no room for zones %s (0x%zx@0x%lx over 0x%lx)\n",
+			name, total_size, *off, info->part_size);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	c = total_size / record_size;
+	zones = kcalloc(c, sizeof(*zones), GFP_KERNEL);
+	if (!zones) {
+		pr_err("allocate for zones %s failed\n", name);
+		return ERR_PTR(-ENOMEM);
+	}
+	memset(zones, 0, c * sizeof(*zones));
+
+	for (i = 0; i < c; i++) {
+		zone = romz_init_zone(type, off, record_size);
+		if (!zone || IS_ERR(zone)) {
+			pr_err("initialize zones %s failed\n", name);
+			while (--i >= 0)
+				kfree(zones[i]);
+			kfree(zones);
+			return (void *)zone;
+		}
+		zones[i] = zone;
+	}
+
+	*cnt = c;
+	return zones;
+}
+
+static void romz_free_zone(struct romz_zone **romzone)
+{
+	struct romz_zone *zone = *romzone;
+
+	if (!zone)
+		return;
+
+	kfree(zone->buffer);
+	kfree(zone);
+	*romzone = NULL;
+}
+
+static void romz_free_zones(struct romz_zone ***romzones, unsigned int *cnt)
+{
+	struct romz_zone **zones = *romzones;
+
+	while (*cnt > 0) {
+		romz_free_zone(&zones[*cnt]);
+		(*cnt)--;
+	}
+	kfree(zones);
+	*romzones = NULL;
+}
+
+static int romz_cut_zones(struct romoops_context *cxt)
+{
+	struct romz_info *info = cxt->rzinfo;
+	unsigned long off = 0;
+	int err;
+	size_t size;
+
+	size = info->part_size;
+	cxt->drzs = romz_init_zones(PSTORE_TYPE_DMESG, &off, size,
+			info->dmesg_size, &cxt->dmesg_max_cnt);
+	if (IS_ERR(cxt->drzs)) {
+		err = PTR_ERR(cxt->drzs);
+		goto fail_out;
+	}
+
+	return 0;
+fail_out:
+	return err;
+}
+
+int romz_register(struct romz_info *info)
+{
+	int err = -EINVAL;
+	struct romoops_context *cxt = &romz_cxt;
+	struct module *owner = info->owner;
+
+	if (!info->part_size || !info->dmesg_size) {
+		pr_warn("The memory size and the dmesg size must be non-zero\n");
+		return -EINVAL;
+	}
+
+	if (info->part_size < 4096) {
+		pr_err("partition size must be over 4096 bytes\n");
+		return -EINVAL;
+	}
+
+#define check_size(name, size) {					\
+		if (info->name & (size)) {				\
+			pr_err(#name " must be a multiple of %d\n",	\
+					(size));			\
+			return -EINVAL;					\
+		}							\
+	}
+
+	check_size(part_size, 4096 - 1);
+	check_size(dmesg_size, SECTOR_SIZE - 1);
+
+#undef check_size
+
+	if (!info->read)
+		info->read = romz_sample_read;
+	if (!info->write)
+		info->write = romz_sample_write;
+
+	if (owner && !try_module_get(owner))
+		return -EINVAL;
+
+	spin_lock(&cxt->rzinfo_lock);
+	if (cxt->rzinfo) {
+		pr_warn("rom '%s' already loaded: ignoring '%s'\n",
+				cxt->rzinfo->name, info->name);
+		spin_unlock(&cxt->rzinfo_lock);
+		return -EBUSY;
+	}
+	cxt->rzinfo = info;
+	spin_unlock(&cxt->rzinfo_lock);
+
+	if (romz_cut_zones(cxt)) {
+		pr_err("cut zones fialed\n");
+		goto fail_out;
+	}
+
+	cxt->pstore.bufsize = cxt->drzs[0]->buffer_size -
+			sizeof(struct romz_dmesg_header);
+	cxt->pstore.buf = kzalloc(cxt->pstore.bufsize, GFP_KERNEL);
+	if (!cxt->pstore.buf) {
+		pr_err("cannot allocate pstore crash dump buffer\n");
+		err = -ENOMEM;
+		goto fail_out;
+	}
+	cxt->pstore.data = cxt;
+	cxt->pstore.flags = PSTORE_FLAGS_DMESG;
+
+	err = pstore_register(&cxt->pstore);
+	if (err) {
+		pr_err("registering with pstore failed\n");
+		goto free_pstore_buf;
+	}
+
+	pr_info("Registered %s as romzone backend for %s%s\n", info->name,
+			cxt->drzs && cxt->rzinfo->dump_oops ? "Oops " : "",
+			cxt->drzs ? "Panic " : "");
+
+	module_put(owner);
+	return 0;
+
+free_pstore_buf:
+	kfree(cxt->pstore.buf);
+fail_out:
+	spin_lock(&romz_cxt.rzinfo_lock);
+	romz_cxt.rzinfo = NULL;
+	spin_unlock(&romz_cxt.rzinfo_lock);
+	return err;
+}
+EXPORT_SYMBOL_GPL(romz_register);
+
+void romz_unregister(struct romz_info *info)
+{
+	struct romoops_context *cxt = &romz_cxt;
+
+	pstore_unregister(&cxt->pstore);
+	kfree(cxt->pstore.buf);
+	cxt->pstore.bufsize = 0;
+
+	spin_lock(&cxt->rzinfo_lock);
+	romz_cxt.rzinfo = NULL;
+	spin_unlock(&cxt->rzinfo_lock);
+
+	romz_free_zones(&cxt->drzs, &cxt->dmesg_max_cnt);
+
+}
+EXPORT_SYMBOL_GPL(romz_unregister);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("liaoweixiong <liaoweixiong@xxxxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Block device Oops/Panic logger");
diff --git a/include/linux/pstore_rom.h b/include/linux/pstore_rom.h
new file mode 100644
index 0000000..45b95df
--- /dev/null
+++ b/include/linux/pstore_rom.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ROMZONE_H_
+#define __ROMZONE_H_
+
+#include <linux/types.h>
+#include <linux/blkdev.h>
+
+#ifndef SECTOR_SIZE
+#define SECTOR_SIZE 512
+#endif
+
+/**
+ * struct romz_info - backend romzone driver structure
+ *
+ * @owner:
+ *	module which is responsible for this backend driver
+ * @name:
+ *	name of the backend driver
+ * @part_path:
+ *	path of a storage partition. It's ok to keep it as NULL
+ *	if you passing @read and @write in romz_info. @part_path
+ *	is needed by stoz_simple_read/write. If both of @part_path,
+ *	@read and @write are NULL, it will temporarity hold the data
+ *	in buffer allocated by 'vmalloc'.
+ * @part_size:
+ *	total size of a storage partition in bytes. The partition
+ *	will be used to save data of pstore.
+ * @dmesg_size:
+ *	the size of each zones for dmesg (oops & panic).
+ * @dump_oops:
+ *	dump oops and panic log or only panic.
+ * @read:
+ *	the normal (not panic) read operation. If NULL, replaced as
+ *	stoz_sample_read. See also @part_path
+ * @write:
+ *	the normal (not panic) write operation. If NULL, replaced as
+ *	stoz_sample_write. See also @part_path
+ * @panic_read:
+ *	the read operation only used for panic.
+ * @panic_write:
+ *	the write operation only used for panic.
+ */
+struct romz_info {
+	struct module *owner;
+	const char *name;
+
+	const char *part_path;
+	unsigned long part_size;
+	unsigned long dmesg_size;
+	int dump_oops;
+	ssize_t (*read)(char *buf, size_t bytes, loff_t pos);
+	ssize_t (*write)(const char *buf, size_t bytes, loff_t pos);
+	ssize_t (*panic_read)(char *buf, size_t bytes, loff_t pos);
+	ssize_t (*panic_write)(const char *buf, size_t bytes, loff_t pos);
+};
+
+extern int romz_register(struct romz_info *info);
+extern void romz_unregister(struct romz_info *info);
+
+#endif
-- 
1.9.1