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

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Message-ID: <CALCETrUDuTt_BK1JSFU=_EEujpm1ekzmkte-c3vxuRW7hWPUPQ@mail.gmail.com>
Date:	Tue, 10 Mar 2015 08:51:59 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Jones <pjones@...hat.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	Sam Protsenko <semen.protsenko@...aro.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 Tue, Mar 10, 2015 at 8:40 AM, Peter Jones <pjones@...hat.com> wrote:
>
>> >> So, for the sysfs interface, let's not allow loading from /lib. Let's
>> >> not require a userland tool. Let's just do,
>> >>
>> >>   # echo /path/to/my/awesome/capsule.bin > /sys/../capsule
>> >
>> >>
>> >> and be done with it.
>> >>
>> >> Hmmm?
>> >
>> > I assume you're implying a) the capsule header with the guid is embedded
>> > in the .bin there already, and b) one contiguous write(2) with error
>> > reporting coming through something like vars.c's efi_status_to_err()?
>> >
>> > If so, yes, I prefer this API.
>> >
>>
>> Is using a char device really so bad?  I have a "simple_char" that
>> makes this really easy that's pending review.
>
> As long as there's straightforward propagation of the EFI_STATUS return
> from UpdateCapsule() back, sysfs file vs char device makes very little
> difference to me.  Either way it's open(), write(), close().  Using the
> runtime firmware upload interface designed for wifi and scsi devices is
> the part I don't really like.
>

I'm not 100% happy with write(2) (which is all we have in sysfs) for
two reasons:

1. If we write a file name, eww.  That's more complicated, requires
temporary files, has annoying mount namespace issues, etc.

2. If we write the full contents, we need to do it in a single call to
write.  That means that we can't use cat, which mostly defeats the
purpose.  In fact, using cat could be actively harmful.


--Andy
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