linux-kernel - Re: can we move USB_DEVICEFS to non-embedded?

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Message-ID: <20090708154758.GB20979@suse.de>
Date:	Wed, 8 Jul 2009 08:47:58 -0700
From:	Greg KH <gregkh@...e.de>
To:	Peter Jones <pjones@...hat.com>
Cc:	Dave Airlie <airlied@...il.com>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Scott James Remnant <scott@...onical.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: can we move USB_DEVICEFS to non-embedded?

On Wed, Jul 08, 2009 at 11:05:38AM -0400, Peter Jones wrote:
> Greg KH wrote:
> > On Wed, Jul 08, 2009 at 10:12:08AM -0400, Peter Jones wrote:
> >> Greg KH wrote:
> >>> On Wed, Jul 08, 2009 at 09:55:04AM -0400, Peter Jones wrote:
> >>>> On 07/08/2009 09:52 AM, Peter Jones wrote:
> >>>>> On 07/08/2009 06:54 AM, Dave Airlie wrote:
> >>>>>
> >>>>>> I'm not quite sure if something in the F11 initrd needs usbfs for
> >>>>>> something (cc'ed Peter)
> >>>>> Not a thing.
> >>>> Actually, I take it back.  We do mount usbfs, and we examine
> >>>> /proc/bus/usb/devices as a heuristic to try and determine if
> >>>> all the devices have been enumerated.
> >>> How can you ever know if all devices are enumerated as you don't know
> >>> how many devices will be showing up?
> >> You don't, that's why I said it's a heuristic.  But basically, we have a 
> >> timeout, and if the device list doesn't change in that amount of time, we
> >> call it done.
> >>
> >> It's not the best technique ever, but it does work.
> > 
> > Works for what?  Why would you want to delay your boot process like
> > this?
> 
> Because otherwise when we actually get to mounting the root filesystem,
> the device *isn't yet present*.

So this is your solution to the "root fs on usb device" problem?  That's
odd that you chose this manner, as it still is not "correct" as has been
seen on different bug reports over the years on lkml.

> >>>> So that could be related to what you're seeing.
> >>> That file is now available in /sys/kernel/debug/usb/devices if you
> >>> really need it.
> >> Oh, okay.  I can change it to use that then.
> >>
> >>> But I would think that you do not.
> >> Well, we pretty much do until we switch to dracut.
> > 
> > What is dracut and why would it change this?
> 
> It's the replacement for mkinitrd, and it's using hotplug events for
> this stuff instead.

Ah, good, yes, that is the correct solution.

> > As no other distro does this kind of waiting, I'm a bit confused as to
> > the need for it.
> 
> Good to know you pay attention to what's going on in the Linux world.

Oh, I do, I just don't think you are noticing us making distros now
without any initrd, or very stripped down ones, in order to achieve fast
boot times.  Look at the moblin images from Intel, or the goblin images
from openSUSE to see that happening today.

So, back to the original problem here, is usbfs a requirement for Fedora
machines to boot properly?  Or has that now been fixed in your repo?

thanks,

greg k-h
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