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

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Date:	Wed, 08 Jul 2009 11:05:38 -0400
From:	Peter Jones <pjones@...hat.com>
To:	Greg KH <gregkh@...e.de>
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?

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 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.

> 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.

-- 
   Peter
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