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

Greg KH
2007-10-25T18:32:23Z

On Thu, Oct 25, 2007 at 05:06:59PM +0800, Dave Young wrote:
> On 10/19/07, Greg KH <greg@kroah.com> wrote:
> >On Wed, Oct 17, 2007 at 10:48:52AM -0400, Alan Stern 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.
> >>
> >> 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...
> >
> >I used to have the 'remove a non-existant file' warning, but that just
> >triggered _way_ too many responses :)
> >
> >
> >> 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);
> >> }
> >
> >If this fixes the problem, care to resend it with a signed-off-by:?
> >
> >Yeah, it's not the nicest solution, but I can't think of any other one
> >either right now :(
> Hi, greg
>
> How about this patch (based on 2.6.24-rc1):
>
> diff -upr linux/drivers/usb/core/message.c linux.new/drivers/usb/core/message.c
> --- linux/drivers/usb/core/message.c 2007-10-25 16:41:32.000000000 +0800
> +++ linux.new/drivers/usb/core/message.c 2007-10-25 16:39:38.000000000 +0800
> @@ -1641,7 +1641,8 @@ free_interfaces:
> intf->dev.bus_id, ret);
> continue;
> }
> - usb_create_sysfs_intf_files (intf);
> + if(!usb_sysfs_intf_exist(intf))
> + usb_create_sysfs_intf_files (intf);
> }
>
> usb_autosuspend_device(dev);
> diff -upr linux/drivers/usb/core/sysfs.c linux.new/drivers/usb/core/sysfs.c
> --- linux/drivers/usb/core/sysfs.c 2007-10-25 16:40:16.000000000 +0800
> +++ linux.new/drivers/usb/core/sysfs.c 2007-10-25 16:39:32.000000000 +0800
> @@ -728,6 +728,13 @@ static inline void usb_remove_intf_ep_fi
> usb_remove_ep_files(&iface_desc->endpoint[i]);
> }
>
> +int usb_sysfs_intf_exist(struct usb_interface *intf)
> +{
> + struct device *dev = &intf->dev;
> +
> + return sysfs_dirent_exist(&dev->kobj, intf_attrs[0]->name);

The issue is that you can't just test for the first file. If you look
at the logic in the usb_create_sysfs_intf_file() code, we do create
different files based on the current interface. So this might not
always end up with the proper files in userspace, from what I can tell.

thanks,

greg k-h