linux-kernel - Re: [patch] add kdump_after

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Date:	Tue, 21 Aug 2007 06:18:31 -0700
From:	Jay Lan <jlan@....com>
To:	vgoyal@...ibm.com
CC:	Takenori Nagano <t-nagano@...jp.nec.com>, k-miyoshi@...jp.nec.com,
	Bernhard Walle <bwalle@...e.de>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Keith Owens <kaos@....com.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] add kdump_after_notifier

Vivek Goyal wrote:
> On Thu, Aug 16, 2007 at 06:26:35PM +0900, Takenori Nagano wrote:
>> Vivek Goyal wrote:
>>  > So for the time being I think we can put RAS tools on die notifier list
>>> and if it runs into issues we can always think of creating a separate list.
>>>
>>> Few things come to mind.
>>>
>>> - Why there is a separate panic_notifier_list? Can't it be merged with
>>>   die_chain? die_val already got one of the event type as PANIC. If there
>>>   are no specific reasons then we should merge the two lists. Registering
>>>   RAS tools on a single list is easier.
>> I think it is difficult, because die_chain is defined by each architecture.
>>
> 
> I think die_chain is arch independent definition (kernel/die_notifier.c)? 
> But anyway, to begin with it can be done only for panic_notifier.
> 
>>> - Modify Kdump to register on die_chain list. 
>>> - Modify Kdb to register on die_chain list.
>>> - Export all the registered members of die_chain through sysfs along with
>>>   their priorities. Priorities should be modifiable. Most likely one 
>>>   shall have to introduce additional field in struct notifier_block. This
>>>   field will be a string as an identifier of the user registerd. e.g
>>>   "Kdump", "Kdb" etc.
>>>
>>> Now user will be able to view all the die_chain users through sysfs and
>>> be able to modify the order in which these should run by modifying their
>>> priority. Hence all the RAS tools can co-exist.
>> This is my image of your proposal.
>>
>> - Print current order
>>
>> # cat /sys/class/misc/debug/panic_notifier_list
>> priority   name
>> 1          IPMI
>> 2          watchdog
>> 3          Kdb
>> 4          Kdump
>>
> 
> I think Bernhard's suggestion looks better here. I noticed that 
> /sys/kernel/debug is already present. So how about following.
> 
> /sys/kernel/debug/kdump/priority
> /sys/kernel/debug/kdb/priority
> /sys/kernel/debug/IPMI/priority

Why separate priority files is better than a central file?
At least i think you get a grand picture of priority being
defined for all parties with a central file?

What do we decide priority if more than one component has
the same priority value?

Thanks,
 - jay

> 
> I think at some point of time we shall have to create another file say
> description.
> 
> /sys/kernel/debug/IPMI/description
> 
> Which can tell what does this tool do? Other a user might not have any
> clue how to prioritize various things.
> 
> Thanks
> Vivek
> 

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