[thirdparty/kernel/stable.git] / Documentation / ramoops.txt

Ramoops oops/panic logger
=========================

Sergiu Iordache <sergiu@chromium.org>

Updated: 8 August 2011

0. Introduction

Ramoops is an oops/panic logger that writes its logs to RAM before the system
crashes. It works by logging oopses and panics in a circular buffer. Ramoops
needs a system with persistent RAM so that the content of that area can
survive after a restart.

1. Ramoops concepts

Ramoops uses a predefined memory area to store the dump. The start and size of
the memory area are set using two variables:
  * "mem_address" for the start
  * "mem_size" for the size. The memory size will be rounded down to a
  power of two.

The memory area is divided into "record_size" chunks (also rounded down to
power of two) and each oops/panic writes a "record_size" chunk of
information.

Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
variable while setting 0 in that variable dumps only the panics.

The module uses a counter to record multiple dumps but the counter gets reset
on restart (i.e. new dumps after the restart will overwrite old ones).

2. Setting the parameters

Setting the ramoops parameters can be done in 2 different manners:
 1. Use the module parameters (which have the names of the variables described
 as before).
 2. Use a platform device and set the platform data. The parameters can then
 be set through that platform data. An example of doing that is:

#include <linux/ramoops.h>
[...]

static struct ramoops_platform_data ramoops_data = {
        .mem_size               = <...>,
        .mem_address            = <...>,
        .record_size            = <...>,
        .dump_oops              = <...>,
};

static struct platform_device ramoops_dev = {
        .name = "ramoops",
        .dev = {
                .platform_data = &ramoops_data,
        },
};

[... inside a function ...]
int ret;

ret = platform_device_register(&ramoops_dev);
if (ret) {
	printk(KERN_ERR "unable to register platform device\n");
	return ret;
}

3. Dump format

The data dump begins with a header, currently defined as "====" followed by a
timestamp and a new line. The dump then continues with the actual data.

4. Reading the data

The dump data can be read from memory (through /dev/mem or other means).
Getting the module parameters, which are needed in order to parse the data, can
be done through /sys/module/ramoops/parameters/* .
Commit	Line	Data
4126dacb SI	1	Ramoops oops/panic logger
	2	=========================
	3
	4	Sergiu Iordache <sergiu@chromium.org>
	5
	6	Updated: 8 August 2011
	7
	8	0. Introduction
	9
	10	Ramoops is an oops/panic logger that writes its logs to RAM before the system
	11	crashes. It works by logging oopses and panics in a circular buffer. Ramoops
	12	needs a system with persistent RAM so that the content of that area can
	13	survive after a restart.
	14
	15	1. Ramoops concepts
	16
	17	Ramoops uses a predefined memory area to store the dump. The start and size of
	18	the memory area are set using two variables:
	19	* "mem_address" for the start
	20	* "mem_size" for the size. The memory size will be rounded down to a
	21	power of two.
	22
	23	The memory area is divided into "record_size" chunks (also rounded down to
	24	power of two) and each oops/panic writes a "record_size" chunk of
	25	information.
	26
	27	Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
	28	variable while setting 0 in that variable dumps only the panics.
	29
	30	The module uses a counter to record multiple dumps but the counter gets reset
	31	on restart (i.e. new dumps after the restart will overwrite old ones).
	32
	33	2. Setting the parameters
	34
	35	Setting the ramoops parameters can be done in 2 different manners:
	36	1. Use the module parameters (which have the names of the variables described
	37	as before).
	38	2. Use a platform device and set the platform data. The parameters can then
	39	be set through that platform data. An example of doing that is:
	40
	41	#include <linux/ramoops.h>
	42	[...]
	43
	44	static struct ramoops_platform_data ramoops_data = {
	45	.mem_size = <...>,
	46	.mem_address = <...>,
	47	.record_size = <...>,
	48	.dump_oops = <...>,
	49	};
	50
	51	static struct platform_device ramoops_dev = {
	52	.name = "ramoops",
	53	.dev = {
	54	.platform_data = &ramoops_data,
	55	},
	56	};
	57
	58	[... inside a function ...]
	59	int ret;
	60
	61	ret = platform_device_register(&ramoops_dev);
	62	if (ret) {
	63	printk(KERN_ERR "unable to register platform device\n");
	64	return ret;
65	}
66
67	3. Dump format
68
69	The data dump begins with a header, currently defined as "====" followed by a
70	timestamp and a new line. The dump then continues with the actual data.
71
72	4. Reading the data
73
74	The dump data can be read from memory (through /dev/mem or other means).
75	Getting the module parameters, which are needed in order to parse the data, can
76	be done through /sys/module/ramoops/parameters/* .