linux-kernel - Re: [patch] add kdump_after

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Date:	Fri, 17 Aug 2007 16:26:30 +0530
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Takenori Nagano <t-nagano@...jp.nec.com>
Cc:	Keith Owens <kaos@....com.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	k-miyoshi@...jp.nec.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bernhard Walle <bwalle@...e.de>
Subject: Re: [patch] add kdump_after_notifier

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

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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