linux-kernel - Re: loading firmware while usermodehelper disabled.

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Message-ID: <20120103003126.52ad9077@pyramind.ukuu.org.uk>
Date:	Tue, 3 Jan 2012 00:31:26 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jack Stone <jwjstone@...tmail.fm>
Cc:	Matthew Garrett <mjg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	Chaoming Li <chaoming_li@...lsil.com.cn>,
	"John W. Linville" <linville@...driver.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>
Subject: Re: loading firmware while usermodehelper disabled.

> So we have a table of USB ids that list the devices that need firmware drivers. When the uvcvideo driver registers the firmware interface with a USB id that matches the list we load the firmware driver and pass it a "warm start" event so it can cache the firmware.
> 
> As long as we can identify the devices that *might* need firmware then we are ok.

You just broke the module loading guarantees that stop it all coming apart
in the first place. Probably not in many real world ways but not good.

If we warm booted from Windows into Linux and then suspended then on
resume we won't have the driver for the firmware loaded present - we
never saw the 'need firmware' id.

That moves us from a dependancy chain for firmware to one including
firmware and modules (imagine /lib/modules over iscsi for an iscsi
adapter needing firmware).

At the moment I don't think anyone has been dumb enough to do firmware
requiring storage and NFS root over firmware requiring USB devices is
pretty dumb. I don't however think it's a good hole to dig ?

Alan

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