linux-kernel - RE: [PATCH v4 2/2] efi: an sysfs interface for user to update efi firmware

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Date:	Mon, 20 Apr 2015 03:28:32 +0000
From:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>
CC:	Ming Lei <ming.lei@...onical.com>,
	"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 2/2] efi: an sysfs interface for user to update efi
 firmware

> -----Original Message-----
> From: Matt Fleming [mailto:matt@...eblueprint.co.uk]
> Sent: Friday, April 17, 2015 10:37 PM
> 
> On Fri, 17 Apr, at 03:49:24PM, Greg KH wrote:
> >
> > Not really, the kernel namespace is what matters at that point in time.
> >
> > And maybe it does matter, I haven't thought through all of the issues.
> > But passing a path from userspace, to the kernel, to have the kernel
> > turn around again and use that path is full of nasty consequences at
> > times due to namespaces, let's avoid all of that please.
> 
> Oh crap. The namespace issue is a good point and not something I'd
> thought of at all.
> 
> At this point, I think we've really run out of objections to Andy's
> suggestion of implementing this as a misc device, right?
> 
> The concern I had about userspace tooling can partly be addressed by
> including the source in tools/ in the kernel tree. So provided we do
> that, I'm happy enough to see this implemented as a misc device because
> the other options we've explored just haven't panned out.
> 
> Objections?
> 
> --
> Matt Fleming, Intel Open Source Technology Center

Hi Greg, Matt & Andy,

Wait .... wait a minute. I am lost. I think I have missed something.
Let me summarize the message I got from the email threads.
=========================================================
Greg:- Recommends to use "cat file.bin > /sys/.../capsule_loader" due to
there is concern on kernel namespace with this submitted design which using
the request firmware API.

Andy:- Prefer to have an interface that could return the error code and
suggested char device where the ioctl can meet the purpose.

Matt:- Prefer to use kernel interface only as embedded world may not want
to include userland tool.
==========================================================

I think I have missed somewhere why not using "cat file.bin > /sys/.../loader"
and now change to misc device. Is it because the ioctl could return a custom
error code (for example: platform not supported, capsule header error)
where the "cat file.bin > /sys/.../loader" interface cannot do? Hmm ......

Regarding the 'reboot require' status, is it critical to have a 1 to 1 status match
with the capsule upload binary? Is it okay to have one sysfs file note to tell the
overall status (for example: 10 capsule binaries uploaded but one require
reboot, so the status shows reboot require is yes)? I am not here trying to argue
anything. I am just trying to find out what kind of info is needed but the sysfs
could not provide. 

Please imagine if your whole Linux system (kernel + rootfs) has to fit into 6MB
space and you don't even have the gcc compiler included into the package.
I believe in this environment, kernel interface + shell command is the only
interaction that user could work with.

Btw, just to make sure I get it correctly, is misc device refer to the device
that created by misc_register() from drivers/char/misc.c and not asked to
put this kernel module under drivers/misc/* location, right?

And Matt mentioned including the source into tools/* in kernel tree. I have
a question: Is this tool can be compiled during kernel compilation and
eventually auto included into the rootfs package? Sorry, I am new to OS
creation and maybe this is stupid question.

Thanks & Regards,
Wilson

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