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Based on kernel version 3.4. Page generated on 2012-05-21 22:09 EST.

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/* .
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