Messages in this thread | | | Date | Sun, 21 Jun 2009 08:58:44 +0200 | From | Pavel Machek <> | Subject | Re: memconsole: a virtual console to record the Oops message for debugging purpose. |
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On Sun 2009-06-14 09:29:48, Changli Gao wrote: > Dear Linus: > > In the production environment, it is hard to find the causion of an > Oops message if a bug causes the kernel panics. Though the Oops > message is printed on the screen, we can't read the whole message in > most cases due to the size of the screen, and it is hard to save the > Oops message for debugging. I know kdump is a choice, but it needs > more memory, and in most cases, Oops messages are enough to find out > the bugs. The other choices are netconsole and serial line, but they > both need extra computers. > > memconsole as a virtual console, will save the messages into a block > of boot memory reserved. Because the memory won't be cleaned(if the > self-check on memory is disabled) between two starts, the oops > messages as the other console messages will be saved between them, and > you have a chance to see what happened in the last start. > > In order to avoid the corruption of the memory used by memconsole, I > find the memory from the end to the start. > > Here is the code, and the code is mess currently. Am I in the right > direction? Are my assumptions right? > > the following code is appended to the file mm/bootmem.c
Generate proper patch...
> void *memconsole_mem_start = NULL; > EXPORT_SYMBOL_GPL(memconsole_mem_start); > unsigned int memconsole_mem_size = 0; > EXPORT_SYMBOL_GPL(memconsole_mem_size); > > static int __init memconsole_setup(char *str) > { > unsigned long start; > > memconsole_mem_size = simple_strtoul(str, NULL, 10); > memconsole_mem_size = PAGE_ALIGN(memconsole_mem_size); > for (start = max_low_pfn - (memconsole_mem_size >> PAGE_SHIFT); > start >= min_low_pfn; > start -= (memconsole_mem_size >> PAGE_SHIFT)) { > if (reserve_bootmem_generic(start << PAGE_SHIFT, > memconsole_mem_size, > BOOTMEM_EXCLUSIVE) >= 0) > break; > } > if (start < min_low_pfn) > panic("Can't reserve bootmem for memconsole\n"); > memconsole_mem_start = phys_to_virt(start << PAGE_SHIFT); > printk("reserve bootmem for memconsole %u@%p\n", > memconsole_mem_size, memconsole_mem_start); > > return 1; > } > __setup("memconsole=", memconsole_setup); > > An individual kernel module is used to implement the whole function.
> Certainly, I tested it on my virtual machine, and I did work.
...and test it on real hw...? Pavel
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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