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