[Crash-utility] question on some command params

Dave Anderson anderson at redhat.com
Tue Sep 30 13:43:24 UTC 2008


Jun Koi wrote:
> On Tue, Sep 23, 2008 at 12:49 AM, Dave Anderson <anderson at redhat.com> wrote:
> 
>>Jun Koi wrote:
>>
>>>Hi,
>>>
>>>I found below cmdline params having no documentation anywhere, so
>>>could somebody explain their meaning?
>>>
>>>- memory_module
>>>- no_modules
>>>- no_ikconfig
>>>- no_namelist_gzip
>>>- no_kmem_cache
>>>- kmem_cache_delay
>>>- readnow
>>>- buildinfo
>>>- zero_excluded
>>>
>>>
>>>Many thanks,
>>>J
>>
>>They're all essentially debug flags for use on kernels/dumpfiles
>>that for some reason or other would not initialize properly.
>>
>>memory_module: if /dev/mem or /dev/crash do not suffice you could
>> force-feed one or the other for live system analysys.
> 
> 
> Another question: Why do we need the "memory_device" param if we
> already had "memory_module"? Arent they the same thing? The naming
> here is so confused to me.

No.

pc->memory_module is the truncated name of a loadable module, if
one is necessary, consisting of the module object file name minus
the ".o" or ".ko", whichever is applicable.  /dev/mem does not
require a pre-installed kernel module, whereas /dev/crash requires
the crash.o or crash.ko misc driver to be installed.  So if by
chance you want to use your own hand-rolled memory device, it may
or may not require that a kernel module be installed.  If it does,
then you would put "--memory_module your-memory-module.ko" on the
command line.

pc->memory_device is the name of a device file, i.e., "/dev/mem"
or "/dev/crash".  It is initialized to "/dev/crash" in hopes that
it exists, and defaults to "/dev/mem" if it doesn't.  But again,
if you have your own memory device you'd like to use, you can override
both of them by putting "--memory_module /dev/whatever" on the command
line.

More important is pc->live_memsrc, which is the name of the live
memory source that is actually used.  The get_live_memory_source()
is the arbitrator function that initializes pc->live_memsrc based
upon:

  1. the system contents (does the crash.[o|ko] module exist?), and
  2. any user overrides using the --memory_module and --memory_device
     command line arguments.

Dave





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