linux-kernel - Re: [linux-usb-devel] usb+sysfs: duplicate filename 'bInterfaceNumber'

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Message-ID: <20071016163348.GB24082@one-eyed-alien.net>
Date:	Tue, 16 Oct 2007 09:33:48 -0700
From:	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <greg@...ah.com>, Dave Young <hidave.darkstar@...il.com>,
	bbpetkov@...oo.de,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] usb+sysfs: duplicate filename 'bInterfaceNumber'

On Tue, Oct 16, 2007 at 10:55:54AM -0400, Alan Stern wrote:
> On Tue, 16 Oct 2007, Dave Young wrote:
> 
> > > I finally duplicated this on one of my machines here at boot time, with
> > > USB built into the kernel.  I'll work tomorrow on tracking this down
> > > further...
> > Hi,
> > I add some printk messages, dump_stack and some others, here is the
> > dmesg dump with debug info(lines begin with "hidave"):
> 
> Okay, good, the extra printk messages show exactly where the problem 
> lies.
> 
> In usb_set_configuration(), each new interfaces is registered and then
> usb_create_sysfs_intf_files() gets called for that interface.  This
> makes sense, because obviously we can't create sysfs files for an
> interface before it is registered.
> 
> The problem is that during registration drivers get probed, and drivers 
> sometimes call usb_set_interface() from their probe method.  This 
> routine also calls usb_create_sysfs_intf_files(), and the result is 
> that the sysfs files get created twice:
> 
> 	First by usb_set_interface, from the driver probe;
> 
> 	Then by usb_set_configuration, when registration is
> 	finished.
> 
> I can think of two possible ways around the problem.  One is to add a 
> bit to the usb_interface structure, recording whether the sysfs files 
> have been created.  The other is always to remove the files just before 
> trying to create them.

I haven't looked at this code at all, but neither approach feels right to
me.

How does this work at all?  Even if you load a driver later, wouldn't it
call usb_set_interface(), which would call usb_create_sysfs_intf_files()
and hit the same issue?

Heck, why do both call usb_create_sysfs_intf_file()?  I would guess if
you're *changing* the active configuration you would need to do that, but
why in usb_set_interface() at all?

Matt

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

I say, what are all those naked people doing?
					-- Big client to Stef
User Friendly, 12/14/1997

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