linux-kernel - Re: [PATCH v4 1/2] firmware_loader: introduce new API

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Message-ID: <CALCETrW_aXJ1iiXCa6aTE3r3J3EF_Njn5bb9=At_3ajCzPFSPg@mail.gmail.com>
Date:	Tue, 14 Apr 2015 11:56:26 -0400
From:	Andy Lutomirski <luto@...capital.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	Ming Lei <ming.lei@...onical.com>,
	Matt Fleming <matt@...sole-pimps.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>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	Peter Jones <pjones@...hat.com>,
	Roy Franz <roy.franz@...aro.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v4 1/2] firmware_loader: introduce new API - request_firmware_direct_full_path()

On Tue, Apr 14, 2015 at 10:08 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Apr 14, 2015 at 05:44:55PM +0800, Kweh, Hock Leong wrote:
>> From: "Kweh, Hock Leong" <hock.leong.kweh@...el.com>
>>
>> Introduce this new API for loading firmware from a specific location
>> instead of /lib/firmware/ by providing a full path to the firmware
>> file.
>
> Ick, why would we want this?
>

Because this mechanism should still work even if /lib is unwriteable
(e.g it's on squashfs or a read-only NFS root).

In this regard, UEFI capsules are very much unlike firmware_class
firmware.  firmware_class firmwise is kind of like device drivers; it
generally comes from the same vendor as your kernel image and
/lib/modules, and it can be updated by the same mechanism.  UEFI
capsules, on the other hand, are one-time things that should be loaded
at the explicit request of the admin.  There is no reason whatsoever
that they should exist on persistent storage, and, in fact, there's a
very good reason that they should not.  On little embedded devices,
which will apparently be the initial users of this code, keeping the
capsules around is a waste of valuable space.

This is why I think that the right approach would be to avoid using
firmware_class entirely for this.  IMO a simple_char device would be
the way to go (hint hint...) but other simple approaches are certainly
possible.

--Andy
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