Documentation: add Ramoops usage description

	- how to get printk format specifiers right

prio_tree.txt

	- info on radix-priority-search-tree use for indexing vmas.

ramoops.txt

	- documentation of the ramoops oops/panic logging module.

rbtree.txt

	- info on what red-black trees are and what they are for.

robust-futex-ABI.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/* .