linux-kernel - RE: [RFC][Patch]efi_pstore:Introduce an efi_pstore_overwrite parameter to avoid missing messages in NVRAM

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2E5A4DB451@USINDEVS01.corp.hds.com>
Date:	Wed, 13 Jun 2012 19:14:16 -0400
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	"Luck, Tony" <tony.luck@...el.com>,
	Mike Waychison <mikew@...gle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"Matthew Garrett (mjg@...hat.com)" <mjg@...hat.com>,
	"gong.chen@...ux.intel.com" <gong.chen@...ux.intel.com>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"rob@...dley.net" <rob@...dley.net>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][Patch]efi_pstore:Introduce an efi_pstore_overwrite
 parameter to avoid missing messages in NVRAM

Thank you for your comment.

> Since the EFI backend has so little storage space ... perhaps it should have some overwrite rules built into it?

I think so.
If multiple triggers don't stride across the reboot, I think we can make an automated rule.

> If this seems a plausible route ... we'd need to tabulate the overwrite rules.  I think they are:
> 	shutdown/reboot/kexec - can be overwritten by OOPS

In my usecase, emergency_restart can be overwritten by OOPS

> 	OOPS can be overwritten by panic
> 	panic can never be overwritten

I can make a patch in accordance with the rule above.

Should it be in pstore layer?
  - introducing a new global variable storing a previous trigger.
  - deciding if we can continue by checking a value of previous trigger at the beginning of pstore_dump().


> I'd like to avoid a kernel parameter ... chances are too high that the machine would be automatically rebooted without the right boot
> argument.

 But, I'm not sure if we can simply apply the rule above in case where multiple triggers stride across the reboot...
In this case,  emergency_restart cannot be overwritten by panic..

Anyway, I will consider the possibility of avoiding a kernel parameter.

Seiji
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