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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/* . |