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Instead of using /dev/mem directly and forcing userspace to know (or extract) where the platform has defined persistent memory, how many slots it has, the sizes, etc, use the common pstore infrastructure to handle Oops gathering and extraction. This presents a much easier to use filesystem-based view to the memory region. This also means that any other tools that are written to understand pstore will automatically be able to process ramoops too. Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Tony Luck <tony.luck@intel.com> Cc: Marco Stornelli <marco.stornelli@gmail.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
77 lines
2.4 KiB
Plaintext
77 lines
2.4 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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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 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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