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

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Message-ID: <a8e1da0710171852s679b57bdp817c3a1d636c1b9d@mail.gmail.com>
Date:	Thu, 18 Oct 2007 09:52:03 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Alan Stern" <stern@...land.harvard.edu>
Cc:	"Matthew Dharm" <mdharm-kernel@...-eyed-alien.net>,
	"Greg KH" <greg@...ah.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 10/17/07, Alan Stern <stern@...land.harvard.edu> wrote:
> On Tue, 16 Oct 2007, Matthew Dharm wrote:
>
> > On Tue, Oct 16, 2007 at 02:04:43PM -0400, Alan Stern wrote:
> > > On Tue, 16 Oct 2007, Matthew Dharm wrote:
> > >
> > > > 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?
> > >
> > > usb_set_interface() is smart enough to remove the old interface files
> > > before creating new ones, since it expects them to exist already.
> > > Hence there's no problem in that scenario.
> > >
> > > But usb_set_configuration doesn't expect there to be any pre-existing
> > > interface files, because there isn't even an interface until the
> > > registration is performed.
> >
> > And I'm guessing that you can't call usb_create_sysfs_intf_files() until
> > registration is performed, right?
>
> Right.
>
> > > The most important reason has to do with the endpoint pseudo-devices.
> > > Different altsettings can have different endpoints, so those have to be
> > > removed and re-created whenever the altsetting changes.
> >
> > Right, altsettings.  I forgot about those.  I only ever think in terms of
> > multiple configurations.
> >
> > *grumble*
> >
> > If usb_set_interface() has to be smart enough to remove existing files
> > first already, then I guess it's reasonably symmetric to have
> > usb_set_configuration() have the same smarts.  Maybe they can share some
> > common code, even.
>
> It's not a big deal to remove the files first.  In fact, here's a patch
> to do it.  Dave, see if this doesn't fix your problem.  I don't like it
> much because it does an unnecessary remove/create cycle, but that's
> better than doing something wrong.

Although it's not the best fix, the problem is fixed, Thanks.

>
> It's slightly odd that the sysfs core logs an error when you try to
> create the same file twice but it doesn't when you try to remove a
> non-existent file (or try to remove an existing file twice).  Oh
> well...
>
> Alan Stern
>
>
>
> Index: usb-2.6/drivers/usb/core/message.c
> ===================================================================
> --- usb-2.6.orig/drivers/usb/core/message.c
> +++ usb-2.6/drivers/usb/core/message.c
> @@ -1643,7 +1643,13 @@ free_interfaces:
>                                 intf->dev.bus_id, ret);
>                         continue;
>                 }
> -               usb_create_sysfs_intf_files (intf);
> +
> +               /* The driver's probe method can call usb_set_interface(),
> +                * which would mean the interface's sysfs files are already
> +                * created.  Just in case, we'll remove them first.
> +                */
> +               usb_remove_sysfs_intf_files(intf);
> +               usb_create_sysfs_intf_files(intf);
>         }
>
>         usb_autosuspend_device(dev);
>
>
-
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