83 lines
2.7 KiB
Plaintext
83 lines
2.7 KiB
Plaintext
Ramoops oops/panic logger
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=========================
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Sergiu Iordache <sergiu@chromium.org>
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Updated: 17 November 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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Ramoops also supports software ECC protection of persistent memory regions.
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This might be useful when a hardware reset was used to bring the machine back
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to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
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corrupt, but usually it is restorable.
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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/pstore_ram.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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.ecc = <...>,
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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 the pstore filesystem. The format for these
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files is "dmesg-ramoops-N", where N is the record number in memory. To delete
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a stored record from RAM, simply unlink the respective pstore file.
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