linux-kernel - Re: Re: [PATCH v2 3/3] efi: Capsule update with user helper interface

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Date:	Thu, 26 Feb 2015 07:30:54 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	Matt Fleming <matt@...sole-pimps.org>,
	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: Re: [PATCH v2 3/3] efi: Capsule update with user helper interface

On Wed, Feb 25, 2015 at 3:47 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Tue, Feb 24, 2015 at 12:49:09PM +0000, Kweh, Hock Leong wrote:
>> So the process steps basically look like this:
>> 1.) cat capsule_ticket    =======> acquire a number and lock mutex then
>>                                                                      expose firmware_class user helper
>>                                                                      interface as well as start timer for timeout
>>                                                                      counting
>> 2.) repeat step 1 if obtained a "0" number
>> 3.) echo 1 > loading
>> 4.) cat bin > data
>> 5.) echo 0 > loading        =======> stop the timeout counting  then unlock
>>                                                                       mutex at the end of callback routine
>> 6.) cat capsule_report   =======> grep the number acquired from beginning
>>                                                                       for checking succeeded/failed
>
> So this sounds pretty overengineered for no reason, or maybe I'm missing
> the reason.
>
> If I had to give an example from the microcode loader, what we do there
> is put the microcode in /lib/firmware/... and do
>
> echo 1 > /sys/devices/system/cpu/microcode/reload
>
> which goes and calls reload_store() in
> arch/x86/kernel/cpu/microcode/core.c which grabs a mutex, disables CPU
> hotplug, etc, etc...
>
> And this mechanism is as simple as it can get. Maybe capsules can be
> loaded like that too?
>
> Error code can be propagated too, if needed, of course.

How can the error code be propagated?  Would that echo command fail in
case of error?

--Andy
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