linux pstore驱动分析和调试

1.简介

pstore（persistent storage）

　　主要用于存储内核异常时的log信息。实现方式是，管理一块“非易失性的存储空间”，如不断电的RAM或外部存储，当系统异常时，将log信息写到Pstore管理的存储空间，直到下一次系统正常时，在将log读出来，以文件形式提供给用户使用。

　　ramoops指的是采用ram保存oops信息的一个功能，在内核开关中用3个开关控制：PSTORE_CONSOLE控制是否保存控制台输出，PSTORE_FTRACE控制是否保存函数调用序列，PSTORE_RAM控制是否保存panic/oops信息。

　　pstore简单来说就是一个小文件系统。主要是读取Android设备内核日志时会用到该模块。

2.整体框架

3. 配置

3.1. dts

32位操作系统如下配置

reserved-memory {

　　#address-cells = <2>;

　　#size-cells = <2>;

　　ranges;

　　reg = <0x50008000 0x100000>;

　　reg-names = "reserved-memory ";

};

ramoops {

　　compatible = "ramoops ";

　　record-size = <0x0 0x20000>;

　　console-size = <0x0 0x20000>;

　　ftrace-size = <0x0 0x20000>;

　　pmsg-size = <0x0 0x20000>;

　　memory-region = <&reserved-memory>;

　　status = "okay";

};

　　由于dts指定的是物理地址，如果内核地址为0x40008000那么可以把pstore地址配置为0x50008000，留出256M空间给内核使用。reg这么配置是32位。每个日志是128KB，总大小是1M，最多可有8个。

3.2. Kconfig

文件路径：linux/fs/pstore/Kconfig

部分内容如下

config PSTORE

tristate "Persistent store support"

select CRYPTO if PSTORE_COMPRESS

default n

help

This option enables generic access to platform level

persistent storage via "pstore" filesystem that can

be mounted as /dev/pstore. Only useful if you have

a platform level driver that registers with pstore to

provide the data, so you probably should just go say "Y"

(or "M") to a platform specific persistent store driver

(e.g. ACPI_APEI on X86) which will select this for you.

If you don't have a platform persistent store driver,

say N.

config PSTORE_CONSOLE

bool "Log kernel console messages"

depends on PSTORE

help

When the option is enabled, pstore will log all kernel

messages, even if no oops or panic happened.

config PSTORE_PMSG

bool "Log user space messages"

depends on PSTORE

help

When the option is enabled, pstore will export a character

interface /dev/pmsg0 to log user space messages. On reboot

data can be retrieved from /sys/fs/pstore/pmsg-ramoops-[ID].

If unsure, say N.

config PSTORE_FTRACE

bool "Persistent function tracer"

depends on PSTORE

depends on FUNCTION_TRACER

depends on DEBUG_FS

help

With this option kernel traces function calls into a persistent

ram buffer that can be decoded and dumped after reboot through

pstore filesystem. It can be used to determine what function

was last called before a reset or panic.

If unsure, say N.

config PSTORE_RAM

tristate "Log panic/oops to a RAM buffer"

depends on PSTORE

depends on HAS_IOMEM

depends on HAVE_MEMBLOCK

select REED_SOLOMON

select REED_SOLOMON_ENC8

select REED_SOLOMON_DEC8

help

This enables panic and oops messages to be logged to a circular

buffer in RAM where it can be read back at some later point.

Note that for historical reasons, the module will be named

"ramoops.ko".

For more information, see Documentation/admin-guide/ramoops.rst.

根据Kconfig文件，对应的配置选项为

选项	Kconfig选项	含义
PSTORE_CONSOLE	Log kernel console messages	内核日志信息
PSTORE_PMSG	Log user space messages	用户日志信息
PSTORE_FTRACE	Persistent function tracer	函数调用关系
PSTORE_RAM	Log panic/oops to a RAM buffer"	内核崩溃或错误日志