linux-kernel - Re: [PATCH] export efi.flags to sysfs

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Message-ID: <CAL01qpvqa-8u2MZ=8wE8gsiprFLbN4U3AbEX9+h7FuemXNR93Q@mail.gmail.com>
Date:	Tue, 27 May 2014 14:36:41 +0100
From:	"Fleming, Matt" <matt.fleming@...el.com>
To:	Dave Young <dyoung@...hat.com>
Cc:	"bp@...en8.de" <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	vgoyal@...hat.com
Subject: Re: [PATCH] export efi.flags to sysfs

On 27 May 2014 04:00, Dave Young <dyoung@...hat.com> wrote:
> On 05/26/14 at 04:39pm, Dave Young wrote:
>>
>> For efi=old_map and any old_map quirks like SGI UV in current
>> tree kexec/kdump will fail because it depends on the new 1:1 mapping.
>>
>> Thus export the mapping method to sysfs so kexec tools can switch
>> to original way to boot.
>>
>> Since we have efi.flags for all efi facilities so let's just export the
>> efi.flags itself, it maybe useful for other arches and use cases.
>
> Rethink about this issue, export flags will expose the efi facility
> macros to userspace, Matt, what's your opinion? It might be better to export
> a file 'old_map' only which is '0|1'

Exporting efi.flags is a non-starter. Those flags are part of an
internal interface and I'm not prepared to turn them into a userspace
ABI that we can never, ever change without a massive amount of pain.

I've only vaguely been following along with the other thread, so please
summarise everything again in your patch. Particularly, I need answers
to the following questions,

 - Are you trying to fix a kexec/kdump regression?
 - Does SGI UV work with kexec + UEFI at all?

The 1:1 mapping was required to make kexec + EFI work in the first
instance. If a machine implements the EFI 1:1 mapping, kexec should
work. If it doesn't implement the 1:1 mapping, then it's probably not
going to work, right?

The crux of the question: are you trying to fix a regression?

If not, then we just need to get SGI UV working with the EFI 1:1
mapping. No?
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