linux-kernel - Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting root

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Message-ID: <20080425153552.GA20918@one-eyed-alien.net>
Date:	Fri, 25 Apr 2008 08:35:52 -0700
From:	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>
To:	Pekka J Enberg <penberg@...helsinki.fi>
Cc:	Greg KH <greg@...ah.com>, Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, dsd@...too.org,
	linux-usb@...r.kernel.org, vegardno@....uio.no,
	James.Bottomley@...senPartnership.com, linux-scsi@...r.kernel.org
Subject: Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting root

On Fri, Apr 25, 2008 at 11:19:02AM +0300, Pekka J Enberg wrote:
> Hi Matthew,
> 
> On Thu, 24 Apr 2008, Matthew Dharm wrote:
> > > > This also has all sorts of races between do_mounts 'waiting' and the actual
> > > > USB device enumeration.  It's entirely possible that the kernel loads via
> > > > BIOS, the USB drivers are loaded, that forces devices to disconnect/reset,
> > > > and they take a while to re-enumerate.  During that delay, the kernel gets
> > > > to do_mount; now, no devices show in this "waiting for scan" count.
> 
> On Fri, Apr 25, 2008 at 09:30:52AM +0300, Pekka J Enberg wrote:
> > > So how does that happen? ->storage_probe fails and driver core calls it 
> > > later at some point?
> 
> On Fri, 25 Apr 2008, Matthew Dharm wrote:
> > There's no guarantee that storage_probe is going to get called in a timely
> > manner.
> 
> How can we add such a guarantee? Don't we have this problem with any other 
> storage devices?

I doubt it.  It all depends on exactly when the USB controller initializes,
all relevant hubs get initialized, and the device finally discovered.

Matt

-- 
Matthew Dharm                              Home: mdharm-usb@...-eyed-alien.net 
Maintainer, Linux USB Mass Storage Driver

I don't have a left mouse button.  I only have one mouse and it's on my right.
					-- Customer
User Friendly, 2/13/1999

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