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author | Sergiu Iordache <sergiu@chromium.org> | 2011-08-13 23:34:56 +0400 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-08-14 05:34:03 +0400 |
commit | 4126dacb5b2ca85b187a27b93805254567526dc8 (patch) | |
tree | 74e37710c4e44b4348569032bc8968a93b715eb3 | |
parent | 6989b5bb2f0302d824bfc5a9272e17eef22353cc (diff) | |
download | linux-4126dacb5b2ca85b187a27b93805254567526dc8.tar.xz |
Documentation: add Ramoops usage description
Add a documentation file describing the usage of Ramoops
Signed-off-by: Sergiu Iordache <sergiu@chromium.org>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | Documentation/00-INDEX | 2 | ||||
-rw-r--r-- | Documentation/ramoops.txt | 76 |
2 files changed, 78 insertions, 0 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index 1f89424c36a6..65bbd2622396 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -272,6 +272,8 @@ printk-formats.txt - 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 diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt new file mode 100644 index 000000000000..8fb1ba7fe7bf --- /dev/null +++ b/Documentation/ramoops.txt @@ -0,0 +1,76 @@ +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/* . |