Re: udev breakages - was: Re: Need of an ".async_probe()" type of callback at driver's core - Was: Re: [PATCH] [media] drxk: change it to use request_firmware_nowait()

From: Ivan Kalvachev <ikalvachev@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>,
	Lennart Poettering <lennart@poettering.net>,
	Greg KH <gregkh@suse.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Kay Sievers <kay@redhat.com>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	Michael Krufky <mkrufky@linuxtv.org>
Subject: Re: udev breakages - was: Re: Need of an ".async_probe()" type of callback at driver's core - Was: Re: [PATCH] [media] drxk: change it to use request_firmware_nowait()
Date: Wed, 3 Oct 2012 00:03:46 +0300	[thread overview]
Message-ID: <CABA=pqdRwA5_AVysq_0ynuChQ++oQ0j2BWyPg4Qq=LjYa-7P2A@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyzXFNq7O+M9EmiRLJ=cDJziipf=BLM8GGAG70j_QTciQ@mail.gmail.com>

On 10/2/12, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Tue, Oct 2, 2012 at 6:03 AM, Mauro Carvalho Chehab
> <mchehab@redhat.com> wrote:
>>
>> I basically tried a few different approaches, including deferred probe(),
>> as you suggested, and request_firmware_async(), as Kay suggested.
>
> Stop this crazy. FIX UDEV ALREADY, DAMMIT.
>
> Who maintains udev these days? Is it Lennart/Kai, as part of systemd?
>
> Lennart/Kai, fix the udev regression already. Lennart was the one who
> brought up kernel ABI regressions at some conference, and if you now
> you have the *gall* to break udev in an incompatible manner that
> requires basically impossible kernel changes for the kernel to "fix"
> the udev interface, I don't know what to say.
>
> "Two-faced lying weasel" would be the most polite thing I could say.
> But it almost certainly will involve a lot of cursing.
>
>> However, for 3.7 or 3.8, I think that the better is to revert changeset
>> 177bc7dade38b5
>> and to stop with udev's insanity of requiring asynchronous firmware load
>> during
>> device driver initialization. If udev's developers are not willing to do
>> that,
>> we'll likely need to add something at the drivers core to trick udev for
>> it to
>> think that the modules got probed before the probe actually happens.
>
> The fact is, udev made new - and insane - rules that are simply
> *invalid*. Modern udev is broken, and needs to be fixed.
>
> I don't know where the problem started in udev, but the report I saw
> was that udev175 was fine, and udev182 was broken, and would deadlock
> if module_init() did a request_firmware(). That kind of nested
> behavior is absolutely *required* to work, in order to not cause
> idiotic problems for the kernel for no good reason.
>
> What kind of insane udev maintainership do we have? And can we fix it?
>
> Greg, I think you need to step up here too. You were the one who let
> udev go. If the new maintainers are causing problems, they need to be
> fixed some way.

I'm not kernel developer and probably my opinion would be a little
naive, but here it is.

Please, make the kernel load firmware from the filesystem on its own.

This should solve almost 99.9% of the problems related to firmware loading.

I don't mind if there is still userland component that could be used
to request a firmware from repository. You can even keep the udev
userland piping as a fallback if you want, but I think you can
simplify a lot of code if you phase it out. The firmware loading
should follow the same concept as modules loading.

I've heard that the udev userland piping of firmware is done to avoid
some licensing issues. But honestly, if you can not store the firmware
on the user's disk, no free operating system should support it at all.

This piping thing have been feature creep that have metastasized all
over the kernel while keeping a lot of obscure modules broken (in hard
to find way) and requiring increasingly complicated schemes to
workaround its flaws.

KiSS.

Best Regards
   Ivan Kalvachev