【调试】pstore原理和使用方法总结

什么是pstore

pstore最初是用于系统发生oops或panic时，自动保存内核log buffer中的日志。不过在当前内核版本中，其已经支持了更多的功能，如保存console日志、ftrace消息和用户空间日志。同时，它还支持将这些消息保存在不同的存储设备中，如内存、块设备或mtd设备。为了提高灵活性和可扩展性，pstore将以上功能分别抽象为前端和后端，其中像dmesg、console等为pstore提供数据的模块称为前端，而内存设备、块设备等用于存储数据的模块称为后端，pstore core则分别为它们提供相关的注册接口。

通过模块化的设计，实现了前端和后端的解耦，因此若某些模块需要利用pstore保存信息，就可以方便地向pstore添加新的前端。而若需要将pstore数据保存到新的存储设备上，也可以通过向其添加后端设备的方式完成。

除此之外，pstore还设计了一套pstore文件系统，用于查询和操作上一次重启时已经保存的pstore数据。当该文件系统被挂载时，保存在backend中的数据将被读取到pstore fs中，并以文件的形式显示。

pstore工作原理

pstore 源文件主要有以下几个：fs/pstore/ram_core.c

fs/pstore/
├── ftrace.c		# ftrace 前端的实现
├── inode.c		# pstore 文件系统的注册与操作
├── internal.h
├── Kconfig
├── Makefile
├── platform.c		# pstore 前后端功能的核心
├── pmsg.c		# pmsg 前端的实现
├── ram.c			# pstore/ram 后端的实现,dram空间分配与管理
├── ram_core.c		# pstore/ram 后端的实现,dram的读写操作

文件创建

pstore文件系统位置在：

# ls /sys/fs/pstore
console-ramoops-0 dmesg-ramoops-0

控制台日志位于 pstore 目录下的console-ramoops文件中，因为采用console机制，该文件中的日志信息也受printk level控制，并不一定是全的。

oops/panic日志位于 pstore 目录下的dmesg-ramoops-x文件中，根据缓冲区大小可以有多个文件，x从0开始。
函数调用序列日志位于 pstore 目录下的ftrace-ramoops文件中。

相关代码在inode.c pstore_mkfile里：

/*
 * Make a regular file in the root directory of our file system.
 * Load it up with "size" bytes of data from "buf".
 * Set the mtime & ctime to the date that this record was originally stored.
 */
int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id, int count,
		  char *data, bool compressed, size_t size,
		  struct timespec time, struct pstore_info *psi)
{
........................

	rc = -ENOMEM;
	inode = pstore_get_inode(pstore_sb);
..............................

	switch (type) {
	case PSTORE_TYPE_DMESG:
		scnprintf(name, sizeof(name), "dmesg-%s-%lld%s",
			  psname, id, compressed ? ".enc.z" : "");
		break;
	case PSTORE_TYPE_CONSOLE:
		scnprintf(name, sizeof(name), "console-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_FTRACE:
		scnprintf(name, sizeof(name), "ftrace-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_MCE:
		scnprintf(name, sizeof(name), "mce-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_PPC_RTAS:
		scnprintf(name, sizeof(name), "rtas-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_PPC_OF:
		scnprintf(name, sizeof(name), "powerpc-ofw-%s-%lld",
			  psname, id);
		break;
	case PSTORE_TYPE_PPC_COMMON:
		scnprintf(name, sizeof(name), "powerpc-common-%s-%lld",
			  psname, id);
		break;
	case PSTORE_TYPE_PMSG:
		scnprintf(name, sizeof(name), "pmsg-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_PPC_OPAL:
		sprintf(name, "powerpc-opal-%s-%lld", psname, id);
		break;
	case PSTORE_TYPE_UNKNOWN:
		scnprintf(name, sizeof(name), "unknown-%s-%lld", psname, id);
		break;
	default:
		scnprintf(name, sizeof(name), "type%d-%s-%lld",
			  type, psname, id);
		break;
	}
....................

	dentry = d_alloc_name(root, name);
.......................

	d_add(dentry, inode);
................
}

pstore_mkfile根据不同的type，使用snprintf函数生成文件名name。生成的文件名格式为<type>-<psname>-<id>，其中type是enum pstore_type_id类型的一个值，psname是给定的psname参数，id是给定的id参数。

接着使用d_alloc_name函数为根目录创建一个目录项dentry，最后使用d_add函数将目录项dentry与索引节点inode关联起来，将其添加到文件系统中。

pstore_register

ramoops负责把message write到某个ram区域上，platform负责从ram读取存到/sys/fs/pstore，ok，先来看机制代码platform.c。

backend需要用pstore_register来注册：

/*
 * platform specific persistent storage driver registers with
 * us here. If pstore is already mounted, call the platform
 * read function right away to populate the file system. If not
 * then the pstore mount code will call us later to fill out
 * the file system.
 */
int pstore_register(struct pstore_info *psi)
{
    struct module *owner = psi->owner;

    if (backend && strcmp(backend, psi->name))
        return -EPERM;

    spin_lock(&pstore_lock);
    if (psinfo) {
        spin_unlock(&pstore_lock);
        return -EBUSY;
    }

    if (!psi->write)
        psi->write = pstore_write_compat;
    if (!psi->write_buf_user)
        psi->write_buf_user = pstore_write_buf_user_compat;
    psinfo = psi;
    mutex_init(&psinfo->read_mutex);
    spin_unlock(&pstore_lock);
    ...
    /*
     * Update the module parameter backend, so it is visible
     * through /sys/module/pstore/parameters/backend
     */
    backend = psi->name;

    module_put(owner);

backend判断确保一次只能有一个并记录了全局psinfo。

看下结构体pstore_info:

struct pstore_info {
    struct module    *owner;
    char        *name;
    spinlock_t    buf_lock;    /* serialize access to 'buf' */
    char        *buf;
    size_t        bufsize;
    struct mutex    read_mutex;    /* serialize open/read/close */
    int        flags;
    int        (*open)(struct pstore_info *psi);
    int        (*close)(struct pstore_info *psi);
    ssize_t        (*read)(u64 *id, enum pstore_type_id *type,
            int *count, struct timespec *time, char **buf,
            bool *compressed, ssize_t *ecc_notice_size,
            struct pstore_info *psi);
    int        (*write)(enum pstore_type_id type,
            enum kmsg_dump_reason reason, u64 *id,
            unsigned int part, int count, bool compressed,
            size_t size, struct pstore_info *psi);
    int        (*write_buf)(enum pstore_type_id type,
            enum kmsg_dump_reason reason, u64 *id,
            unsigned int part, const char *buf, bool compressed,
            size_t size, struct pstore_info *psi);
    int        (*write_buf_user)(enum pstore_type_id type,
            enum kmsg_dump_reason reason, u64 *id,
            unsigned int part, const char __user *buf,
            bool compressed, size_t size, struct pstore_info *psi);
    int        (*erase)(enum pstore_type_id type, u64 id,
            int count, struct timespec time,
            struct pstore_info *psi);
    void        *data;
};

name就是backend的name了。

*write和*write_buf_user如果backend没有给出会有个默认compat func，最终都走的*write_buf。

if (!psi->write)
        psi->write = pstore_write_compat;
    if (!psi->write_buf_user)
        psi->write_buf_user = pstore_write_buf_user_compat;

static int pstore_write_compat(enum pstore_type_id type,
                   enum kmsg_dump_reason reason,
                   u64 *id, unsigned int part, int count,
                   bool compressed, size_t size,
                   struct pstore_info *psi)
{
    return psi->write_buf(type, reason, id, part, psinfo->buf, compressed,
                 size, psi);
}

static int pstore_write_buf_user_compat(enum pstore_type_id type,
                   enum kmsg_dump_reason reason,
                   u64 *id, unsigned int part,
                   const char __user *buf,
                   bool compressed, size_t size,
                   struct pstore_info *psi)
{
...
        ret = psi->write_buf(type, reason, id, part, psinfo->buf,
...
}

继续pstore注册：

 if (pstore_is_mounted())
        pstore_get_records(0);

如果pstore已经mounted，那就创建并填充文件by pstore_get_records:

/*
 * Read all the records from the persistent store. Create
 * files in our filesystem.  Don't warn about -EEXIST errors
 * when we are re-scanning the backing store looking to add new
 * error records.
 */
void pstore_get_records(int quiet)
{
    struct pstore_info *psi = psinfo; //tj: global psinfo
    ...
    mutex_lock(&psi->read_mutex);
    if (psi->open && psi->open(psi))
        goto out;

    while ((size = psi->read(&id, &type, &count, &time, &buf, &compressed,
                 &ecc_notice_size, psi)) > 0) {
        if (compressed && (type == PSTORE_TYPE_DMESG)) {
            if (big_oops_buf)
                unzipped_len = pstore_decompress(buf,
                            big_oops_buf, size,
                            big_oops_buf_sz);

            if (unzipped_len > 0) {
                if (ecc_notice_size)
                    memcpy(big_oops_buf + unzipped_len,
                           buf + size, ecc_notice_size);
                kfree(buf);
                buf = big_oops_buf;
                size = unzipped_len;
                compressed = false;
            } else {
                pr_err("decompression failed;returned %d\n",
                       unzipped_len);
                compressed = true;
            }
        }
        rc = pstore_mkfile(type, psi->name, id, count, buf,
                   compressed, size + ecc_notice_size,
                   time, psi);
        if (unzipped_len < 0) {
            /* Free buffer other than big oops */
            kfree(buf);
            buf = NULL;
        } else
            unzipped_len = -1;
        if (rc && (rc != -EEXIST || !quiet))
            failed++;
    }
    if (psi->close)
        psi->close(psi);
out:
    mutex_unlock(&psi->read_mutex);

if needed，call pstore_decompress解压然后创建pstore文件by vfs接口pstore_mkfile。

pstore注册接下来是按类别分别注册：

    if (psi->flags & PSTORE_FLAGS_DMESG)
        pstore_register_kmsg();
    if (psi->flags & PSTORE_FLAGS_CONSOLE)
        pstore_register_console();
    if (psi->flags & PSTORE_FLAGS_FTRACE)
        pstore_register_ftrace();
    if (psi->flags & PSTORE_FLAGS_PMSG)
        pstore_register_pmsg();

psi->flags仍是由backend决定，只看pstore_register_kmsg和pstore_register_console。

pstore panic log注册

static struct kmsg_dumper pstore_dumper = {
    .dump = pstore_dump,
};

/*
 * Register with kmsg_dump to save last part of console log on panic.
 */
static void pstore_register_kmsg(void)
{
    kmsg_dump_register(&pstore_dumper);
}

pstore_dump最终会call backend的write，直接用全局psinfo。

/*
 * callback from kmsg_dump. (s2,l2) has the most recently
 * written bytes, older bytes are in (s1,l1). Save as much
 * as we can from the end of the buffer.
 */
static void pstore_dump(struct kmsg_dumper *dumper,
            enum kmsg_dump_reason reason)
{
    ...
        ret = psinfo->write(PSTORE_TYPE_DMESG, reason, &id, part,
                    oopscount, compressed, total_len, psinfo);

kmsg_dump_register是内核一种增加log dumper方法，called when kernel oopses or panic。

/**
 * kmsg_dump_register - register a kernel log dumper.
 * @dumper: pointer to the kmsg_dumper structure
 *
 * Adds a kernel log dumper to the system. The dump callback in the
 * structure will be called when the kernel oopses or panics and must be
 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
 */
int kmsg_dump_register(struct kmsg_dumper *dumper)
{
	unsigned long flags;
	int err = -EBUSY;

	/* The dump callback needs to be set */
	if (!dumper->dump)
		return -EINVAL;

	spin_lock_irqsave(&dump_list_lock, flags);
	/* Don't allow registering multiple times */
	if (!dumper->registered) {
		dumper->registered = 1;
		list_add_tail_rcu(&dumper->list, &dump_list);
		err = 0;
	}
	spin_unlock_irqrestore(&dump_list_lock, flags);

	return err;
}

/**
 * kmsg_dump - dump kernel log to kernel message dumpers.
 * @reason: the reason (oops, panic etc) for dumping
 *
 * Call each of the registered dumper's dump() callback, which can
 * retrieve the kmsg records with kmsg_dump_get_line() or
 * kmsg_dump_get_buffer().
 */
void kmsg_dump(enum kmsg_dump_reason reason)
{
	struct kmsg_dumper *dumper;
	unsigned long flags;

	if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
		return;

	rcu_read_lock();
	list_for_each_entry_rcu(dumper, &dump_list, list) {
		if (dumper->max_reason && reason > dumper->max_reason)
			continue;

		/* initialize iterator with data about the stored records */
		dumper->active = true;

		raw_spin_lock_irqsave(&logbuf_lock, flags);
		dumper->cur_seq = clear_seq;
		dumper->cur_idx = clear_idx;
		dumper->next_seq = log_next_seq;
		dumper->next_idx = log_next_idx;
		raw_spin_unlock_irqrestore(&logbuf_lock, flags);

		/* invoke dumper which will iterate over records */
		dumper->dump(dumper, reason);

		/* reset iterator */
		dumper->active = false;
	}
	rcu_read_unlock();
}

pstore console 注册

static struct console pstore_console = {
    .name    = "pstore",
    .write    = pstore_console_write,
    .flags    = CON_PRINTBUFFER | CON_ENABLED | CON_ANYTIME,
    .index    = -1,
};

static void pstore_register_console(void)
{
    register_console(&pstore_console);
}

->write最终也会call backend write:

#ifdef CONFIG_PSTORE_CONSOLE
static void pstore_console_write(struct console *con, const char *s, unsigned c)
{
    const char *e = s + c;

    while (s < e) {
        unsigned long flags;
        u64 id;

        if (c > psinfo->bufsize)
            c = psinfo->bufsize;

        if (oops_in_progress) {
            if (!spin_trylock_irqsave(&psinfo->buf_lock, flags))
                break;
        } else {
            spin_lock_irqsave(&psinfo->buf_lock, flags);
        }
        memcpy(psinfo->buf, s, c);
        psinfo->write(PSTORE_TYPE_CONSOLE, 0, &id, 0, 0, 0, c, psinfo);  // tj: here
        spin_unlock_irqrestore(&psinfo->buf_lock, flags);
        s += c;
        c = e - s;
    }
}

ramoops

下面来看下RAM backend: ramoops，先看probe:

static int ramoops_probe(struct platform_device *pdev)
{
    struct device *dev = &pdev->dev;
    struct ramoops_platform_data *pdata = dev->platform_data;
    ...

    if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size &&
            !pdata->ftrace_size && !pdata->pmsg_size)) {
        pr_err("The memory size and the record/console size must be "
            "non-zero\n");
        goto fail_out;
    }
    ...
    
    cxt->size = pdata->mem_size;
    cxt->phys_addr = pdata->mem_address;
    cxt->memtype = pdata->mem_type;
    cxt->record_size = pdata->record_size;
    cxt->console_size = pdata->console_size;
    cxt->ftrace_size = pdata->ftrace_size;
    cxt->pmsg_size = pdata->pmsg_size;
    cxt->dump_oops = pdata->dump_oops;
    cxt->ecc_info = pdata->ecc_info;

pdata应该来源ramoops_register_dummy:

static void ramoops_register_dummy(void)
{
    ...
    pr_info("using module parameters\n");

    dummy_data = kzalloc(sizeof(*dummy_data), GFP_KERNEL);
    if (!dummy_data) {
        pr_info("could not allocate pdata\n");
        return;
    }

    dummy_data->mem_size = mem_size;
    dummy_data->mem_address = mem_address;
    dummy_data->mem_type = mem_type;
    dummy_data->record_size = record_size;
    dummy_data->console_size = ramoops_console_size;
    dummy_data->ftrace_size = ramoops_ftrace_size;
    dummy_data->pmsg_size = ramoops_pmsg_size;
    dummy_data->dump_oops = dump_oops;
    /*
     * For backwards compatibility ramoops.ecc=1 means 16 bytes ECC
     * (using 1 byte for ECC isn't much of use anyway).
     */
    dummy_data->ecc_info.ecc_size = ramoops_ecc == 1 ? 16 : ramoops_ecc;

    dummy = platform_device_register_data(NULL, "ramoops", -1,
            dummy_data, sizeof(struct ramoops_platform_data));

有几个可配参数:

/*
 * Ramoops platform data
 * @mem_size    memory size for ramoops
 * @mem_address    physical memory address to contain ramoops
 */

struct ramoops_platform_data {
    unsigned long    mem_size;  
    phys_addr_t    mem_address; 
    unsigned int    mem_type;
    unsigned long    record_size;
    unsigned long    console_size;
    unsigned long    ftrace_size;
    unsigned long    pmsg_size;
    int        dump_oops;
    struct persistent_ram_ecc_info ecc_info;
};

mem_size：用于Ramoops的内存大小，表示分配给Ramoops的物理内存的大小。
mem_address：用于Ramoops的物理内存地址，指定用于存储Ramoops的物理内存的起始地址。
mem_type：内存类型，用于进一步描述内存的属性和特征。
record_size：每个记录的大小
console_size：控制台记录的大小
ftrace_size：Ftrace记录的大小
pmsg_size：pmsg消息记录的大小
dump_oops：是否转储oops信息的标志，表示是否将oops信息转储到Ramoops中。
ecc_info：RAM的ECC（纠错码）信息，用于提供关于ECC配置和处理的详细信息。

有个结构表示了ramoops的context:

struct ramoops_context {
    struct persistent_ram_zone **przs;
    struct persistent_ram_zone *cprz;
    struct persistent_ram_zone *fprz;
    struct persistent_ram_zone *mprz;
    phys_addr_t phys_addr;
    unsigned long size;
    unsigned int memtype;
    size_t record_size;
    size_t console_size;
    size_t ftrace_size;
    size_t pmsg_size;
    int dump_oops;
    struct persistent_ram_ecc_info ecc_info;
    unsigned int max_dump_cnt;
    unsigned int dump_write_cnt;
    /* _read_cnt need clear on ramoops_pstore_open */
    unsigned int dump_read_cnt;
    unsigned int console_read_cnt;
    unsigned int ftrace_read_cnt;
    unsigned int pmsg_read_cnt;
    struct pstore_info pstore;
};

在ramoops_probe时也是把ramoops_platform_data的成员赋给了context对应的。要了解具体含义，继续probe:

    paddr = cxt->phys_addr;

    dump_mem_sz = cxt->size - cxt->console_size - cxt->ftrace_size
            - cxt->pmsg_size;
    err = ramoops_init_przs(dev, cxt, &paddr, dump_mem_sz);
    if (err)
        goto fail_out;

    err = ramoops_init_prz(dev, cxt, &cxt->cprz, &paddr,
                   cxt->console_size, 0);
    if (err)
        goto fail_init_cprz;

    err = ramoops_init_prz(dev, cxt, &cxt->fprz, &paddr, cxt->ftrace_size,
                   LINUX_VERSION_CODE);
    if (err)
        goto fail_init_fprz;

    err = ramoops_init_prz(dev, cxt, &cxt->mprz, &paddr, cxt->pmsg_size, 0);
    if (err)
        goto fail_init_mprz;

    cxt->pstore.data = cxt;

可见，是逐个init每个persistant ram zone，size一共有4段：

dump_mem_sz + cxt->console_size + cxt->ftrace_size + cxt->pmsg_size = cxt->size

mem_size就是总大小了，mem_address是ramoops的物理地址，record_size再看下oops/panic ram：

static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
                 phys_addr_t *paddr, size_t dump_mem_sz)
{
    int err = -ENOMEM;
    int i;

    if (!cxt->record_size)
        return 0;

    if (*paddr + dump_mem_sz - cxt->phys_addr > cxt->size) {
        dev_err(dev, "no room for dumps\n");
        return -ENOMEM;
    }

    cxt->max_dump_cnt = dump_mem_sz / cxt->record_size;
    if (!cxt->max_dump_cnt)
        return -ENOMEM;

ok dump_mem_size大小的区域分成max_dump_cnt个，每个记录大小是record_size。

接着会call persistent_ram_new来分配内存给这个ram zone。

    for (i = 0; i < cxt->max_dump_cnt; i++) {
        cxt->przs[i] = persistent_ram_new(*paddr, cxt->record_size, 0,
                          &cxt->ecc_info,
                          cxt->memtype, 0);

console/ftrace/pmsg ram zone同上分配。

最后处理flags并注册pstore:

    cxt->pstore.flags = PSTORE_FLAGS_DMESG; //tj: 默认dump oops/panic
    if (cxt->console_size)
        cxt->pstore.flags |= PSTORE_FLAGS_CONSOLE;
    if (cxt->ftrace_size)
        cxt->pstore.flags |= PSTORE_FLAGS_FTRACE;
    if (cxt->pmsg_size)
        cxt->pstore.flags |= PSTORE_FLAGS_PMSG;

    err = pstore_register(&cxt->pstore);
    if (err) {
        pr_err("registering with pstore failed\n");
        goto fail_buf;
    }

来看下ramoops pstore的定义的callback，他们通过全局psinfo而来：

static struct ramoops_context oops_cxt = {
    .pstore = {
        .owner    = THIS_MODULE,
        .name    = "ramoops",
        .open    = ramoops_pstore_open,
        .read    = ramoops_pstore_read, // psi->read
        .write_buf    = ramoops_pstore_write_buf, //for non pmsg
        .write_buf_user    = ramoops_pstore_write_buf_user, //for pmsg
        .erase    = ramoops_pstore_erase,
    },
};

pstore使用方法

ramoops

配置内核

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_PSTORE_RAM=y
CONFIG_PANIC_TIMEOUT=-1

由于log数据存放于DDR，不能掉电，只能依靠自动重启机制来查看，故而要配置：CONFIG_PANIC_TIMEOUT，让系统在 panic 后能自动重启。

dts

ramoops_mem: ramoops_mem {
    reg = <0x0 0x110000 0x0 0xf0000>;
    reg-names = "ramoops_mem";
};

ramoops {
    compatible = "ramoops";
    record-size = <0x0 0x20000>;
    console-size = <0x0 0x80000>;
    ftrace-size = <0x0 0x00000>;
    pmsg-size = <0x0 0x50000>;
    memory-region = <&ramoops_mem>;
};

mtdoops

内核配置

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_MTD_OOPS=y
CONFIG_MAGIC_SYSRQ=y

分区配置

cmdline方式：

bootargs = "console=ttyS1,115200 loglevel=8 rootwait root=/dev/mtdblock5 rootfstype=squashfs mtdoops.mtddev=pstore";

blkparts = "mtdparts=spi0.0:64k(spl)ro,256k(uboot)ro,64k(dtb)ro,128k(pstore),3m(kernel)ro,4m(rootfs)ro,-(data)";

part of方式：

bootargs = "console=ttyS1,115200 loglevel=8 rootwait root=/dev/mtdblock5 rootfstype=squashfs mtdoops.mtddev=pstore";

partition@60000 {
    label = "pstore";
    reg = <0x60000 0x20000>;
 };

blkoops

配置内核

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_PSTORE_BLK=y
CONFIG_MTD_PSTORE=y
CONFIG_MAGIC_SYSRQ=y

配置分区

cmdline方式：

bootargs = "console=ttyS1,115200 loglevel=8 rootwait root=/dev/mtdblock5 rootfstype=squashfs pstore_blk.blkdev=pstore";

blkparts = "mtdparts=spi0.0:64k(spl)ro,256k(uboot)ro,64k(dtb)ro,128k(pstore),3m(kernel)ro,4m(rootfs)ro,-(data)";

part of方式：

bootargs = "console=ttyS1,115200 loglevel=8 rootwait root=/dev/mtdblock5 rootfstype=squashfs pstore_blk.blkdev=pstore";

partition@60000 {
    label = "pstore";
    reg = <0x60000 0x20000>;
};

pstore fs

挂载pstore文件系统

mount -t pstore pstore /sys/fs/pstore

挂载后，通过mount能看到类似这样的信息：

# mount
pstore on /sys/fs/pstore type pstore (rw,relatime)

如果需要验证，可以这样主动触发内核崩溃：

# echo c > /proc/sysrq-trigger

不同配置方式日志名称不同

ramoops

# mount -t pstore pstore /sys/fs/pstore/
# cd /sys/fs/pstore/
# ls
console-ramoops-0  dmesg-ramoops-0    dmesg-ramoops-1

mtdoops

# cat /dev/mtd3 > 1.txt
# cat 1.txt

blkoops

cd /sys/fs/pstore/
ls
dmesg-pstore_blk-0  dmesg-pstore_blk-1

总结

pstore setup 流程：

ramoops_init
ramoops_register_dummy
ramoops_probe
ramoops_register

查看 pstore 数据保存流程：

register a pstore_dumper
// when panic happens, kmsg_dump is called
call dumper->dump
pstore_dump

查看 pstore 数据读取流程：

ramoops_probe
persistent_ram_post_init
pstore_register
pstore_get_records
ramoops_pstore_read
pstore_decompress (only for dmesg)
pstore_mkfile (save to files)