Message-ID: <20060830205739.GA26475@powerlinux.fr>
Date:	Wed, 30 Aug 2006 22:57:39 +0200
From:	Sven Luther <sven.luther@...adoo.fr>
To:	David Lang <dlang@...italinsight.com>
Cc:	Sven Luther <sven.luther@...adoo.fr>, Olaf Hering <olaf@...fle.de>,
	Michael Buesch <mb@...sch.de>, Greg KH <greg@...ah.com>,
	Oleg Verych <olecom@...wer.upol.cz>,
	James Bottomley <James.Bottomley@...eleye.com>,
	debian-kernel@...ts.debian.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MODULE_FIRMWARE for binary firmware(s)

On Wed, Aug 30, 2006 at 12:34:16PM -0700, David Lang wrote:
> On Wed, 30 Aug 2006, Sven Luther wrote:
> 
> >>>
> >>>Do you really need to bring up ipw2200 so early ? It is some kind of
> >>>wireless
> >>>device, right ?
> >>
> >>if modules are not in use the device is initialized when the kernel starts
> >>up. this is before any userspace starts.
> >
> >Well. but you could do the initialization at open time too, like the other
> >case that was mentioned here, no ?
> 
> no, at least not in the current kernel. as was mentioned earlier in this 
> thread the ipw2200 needs the firmware at initialization, but some others 
> don't need it until open. I don't know if it's even possible to re-write 
> the driver to do this.

Oh well, this doesn't explain why it is so, but i suppose you know what you
speak about.

> >>>As for initramfs, you can just cat it behind the kernel, and it should 
> >>>work
> >>>just fine, or at least this is how it was supposed to work.
> >>
> >>yes, if I want to set one up.
> >>
> >>other then this new requirement to have the ipw2200 driver as a module I
> >>have no reason to use one. normal userspace is good enough for me.
> >
> >Well, ok.
> >
> >The real question seems to be if we want to keep the firmware inside the
> >driver or not.
> >
> >If we want to remove it, then we put, not the module, but the firmware 
> >itself
> >with some basic userspace to load it on demand in the initramfs, and this 
> >is
> >reason enough to create an initramfs. The fact that the builtin device is
> >initialized before the initramfs is loaded seems like a bug to me, since 
> >the
> >idea of the initramfs (well, one of them at least), was to initialize it 
> >early
> >enough for this kind of things.
> 
> this isn't my understanding.

Indeed, in the initrd era, the ramdisk was initialized too late for this kind
of stuff, but it was one of the features of the initramfs ramdisks to
initialize it earlier, which made firmware loading possible.

> my understanding is that the kernel fully initializes all built-in drivers, 
> then loads userspace and starts running it.

Well, there is userspace and userspace.

> that userspace can be on a device that it knows how to read, or it can be 
> userspace on initramfs so that you can load additional modules to give you 
> access to the hardware that you want to run on.

Yep, but initramfs is initialized ways earlier than normal userspace.

> this is needed if your root drive is a SCSI drive and you have it's driver 
> compiled as a module for example.

Ok.

> this is needed if your root drive uses dm and you need to initialize the 
> array (one advantage of md, from the user standpoint, is that it doesn't 
> require this additional layer before use)

Ok.

> however this is not soon enough to supply the firmware for devices like 
> this.

Are you sure of this ? This is somewhat contrary to what i have heard, and it
sure would make sense to be able to access the initramfs ramdisk much earlier.

> >If on the other side, it is more important to not have an initramfs 
> >(because
> >of security issues, or bootloader constraints or what not), then sure, 
> >there
> >is not much choice than putting the firmware in the driver or in the kernel
> >directly.
> >
> >But again, the initramfs is just a memory space available at the end of the
> >kernel, and there is no hardware-related constraint to access it which are 
> >in
> >any way different from having the firmware linked in together with the 
> >kernel,
> >so it is only a matter of organisation of code, as well as taking a 
> >decision
> >on the above, and to act accordyingly.
> 
> if the firmware needed for any drivers compiled in was appended to the 
> kernel the same way that initramfs is, without requireing the other things 
> needed to make initrmfs useable I think that would be reasonable (bundling 
> them togeather as opposed to embedding the firmware in the kernel). it may 
> even be possible to have the firmware as files in a initramfs that contains 
> nothing else, and the kernel knows how to read the data directly (without 
> the hotplug firmware request userspace stuff)

Indeed, and it seems to me that exactly this kind of use was indeed considered
when the initramfs infrastructure was designed. Not sure about the latest bit
concerning hotplug though.

> >Does using an initramfs really have some negative side, security related ?
> >Would some kind of signed or encrypted initramfs be preferable there ?
> 
> adding an initramfs to a system that doesn't need it otherwise adds 
> complications to the configure and boot process.

Yeah, well, if it is just cated at the end of the kernel, it would be rather
minimal.

> requireing modules when they weren't required before adds complication, and 
> if/when the patch that's floating around to eliminate access to /dev/kmem 
> is ever accepted, there are security advantages of running a kernel that 
> doesn't have any support for run-time modifications (i.e. module loading).

Indeed.

> I realize that many people want to make initramfs mandatory (with things 
> like partition detection moved to userspace), but unless there is a 
> standard initramfs that is shipped and maintained with the kernel to 
> implement things like this (see the klibc discussion a few weeks ago) you 
> are adding complications without much of a benifit to the user.

Well, since debian moved to 2.6 kernels on powerpc, i have been using ramdisks,
and let me assure you that from a distribution point of view, it is way more
elegant and nice than the non-ramdisk solution.

Friendly,

Sven Luther
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