Root/Documentation/ramoops.txt

1Ramoops oops/panic logger
2=========================
3
4Sergiu Iordache <sergiu@chromium.org>
5
6Updated: 8 August 2011
7
80. Introduction
9
10Ramoops is an oops/panic logger that writes its logs to RAM before the system
11crashes. It works by logging oopses and panics in a circular buffer. Ramoops
12needs a system with persistent RAM so that the content of that area can
13survive after a restart.
14
151. Ramoops concepts
16
17Ramoops uses a predefined memory area to store the dump. The start and size of
18the 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
23The memory area is divided into "record_size" chunks (also rounded down to
24power of two) and each oops/panic writes a "record_size" chunk of
25information.
26
27Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
28variable while setting 0 in that variable dumps only the panics.
29
30The module uses a counter to record multiple dumps but the counter gets reset
31on restart (i.e. new dumps after the restart will overwrite old ones).
32
332. Setting the parameters
34
35Setting 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
44static struct ramoops_platform_data ramoops_data = {
45        .mem_size = <...>,
46        .mem_address = <...>,
47        .record_size = <...>,
48        .dump_oops = <...>,
49};
50
51static struct platform_device ramoops_dev = {
52        .name = "ramoops",
53        .dev = {
54                .platform_data = &ramoops_data,
55        },
56};
57
58[... inside a function ...]
59int ret;
60
61ret = platform_device_register(&ramoops_dev);
62if (ret) {
63    printk(KERN_ERR "unable to register platform device\n");
64    return ret;
65}
66
673. Dump format
68
69The data dump begins with a header, currently defined as "====" followed by a
70timestamp and a new line. The dump then continues with the actual data.
71
724. Reading the data
73
74The dump data can be read from memory (through /dev/mem or other means).
75Getting the module parameters, which are needed in order to parse the data, can
76be done through /sys/module/ramoops/parameters/* .
77

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