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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>
authored by
Sergiu Iordache
and committed by
Linus Torvalds
4126dacb
6989b5bb
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Documentation/00-INDEX
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Documentation/00-INDEX
···
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- how to get printk format specifiers right
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prio_tree.txt
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- info on radix-priority-search-tree use for indexing vmas.
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ramoops.txt
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- documentation of the ramoops oops/panic logging module.
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rbtree.txt
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- info on what red-black trees are and what they are for.
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robust-futex-ABI.txt
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Documentation/ramoops.txt
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Documentation/ramoops.txt
···
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Ramoops oops/panic logger
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=========================
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Sergiu Iordache <sergiu@chromium.org>
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Updated: 8 August 2011
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0. Introduction
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Ramoops is an oops/panic logger that writes its logs to RAM before the system
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crashes. It works by logging oopses and panics in a circular buffer. Ramoops
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needs a system with persistent RAM so that the content of that area can
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survive after a restart.
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1. Ramoops concepts
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Ramoops uses a predefined memory area to store the dump. The start and size of
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the memory area are set using two variables:
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* "mem_address" for the start
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* "mem_size" for the size. The memory size will be rounded down to a
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power of two.
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The memory area is divided into "record_size" chunks (also rounded down to
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power of two) and each oops/panic writes a "record_size" chunk of
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information.
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Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
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variable while setting 0 in that variable dumps only the panics.
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The module uses a counter to record multiple dumps but the counter gets reset
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on restart (i.e. new dumps after the restart will overwrite old ones).
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2. Setting the parameters
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Setting the ramoops parameters can be done in 2 different manners:
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1. Use the module parameters (which have the names of the variables described
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as before).
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2. Use a platform device and set the platform data. The parameters can then
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be set through that platform data. An example of doing that is:
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#include <linux/ramoops.h>
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[...]
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static struct ramoops_platform_data ramoops_data = {
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.mem_size = <...>,
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.mem_address = <...>,
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.record_size = <...>,
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.dump_oops = <...>,
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};
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static struct platform_device ramoops_dev = {
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.name = "ramoops",
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.dev = {
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.platform_data = &ramoops_data,
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},
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};
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[... inside a function ...]
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int ret;
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ret = platform_device_register(&ramoops_dev);
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if (ret) {
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printk(KERN_ERR "unable to register platform device\n");
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return ret;
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}
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3. Dump format
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The data dump begins with a header, currently defined as "====" followed by a
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timestamp and a new line. The dump then continues with the actual data.
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4. Reading the data
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The dump data can be read from memory (through /dev/mem or other means).
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Getting the module parameters, which are needed in order to parse the data, can
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be done through /sys/module/ramoops/parameters/* .