Am Mittwoch, 15. März 2006 20:29 schrieb Alan Stern:
> On Wed, 15 Mar 2006, Paul Fulghum wrote:
>
> > On Wed, 2006-03-15 at 11:56 -0500, Alan Stern wrote:
> > > > Should driver core defer sysfs_remove_file until
> > > > last dev->kobj reference is dropped?
> > >
> > > No. The files should be deleted. James Bottomley refers to this as
> > > "removing from visibility". There's no point leaving the symlink visible
> > > once it can no longer be used.
> > >
> > > Instead, the code should be fixed so that the attempt to remove the
> > > already-deleted symlink by class_device_del() doesn't cause an oops.
> >
> > So dev->kobj->dentry should be set to NULL in
> > device_remove_file() and other code should be
> > fixed to check for dev->kobj->dentry == NULL ?
>
> I don't know. I'm not familiar with the details of how sysfs is supposed
> to work. Maybe the existence of the symlink should prevent the dentry
> from being freed during sysfs_remove_dir. Or maybe sysfs_remove_dir
> should modify the symlink data structure so that the other code would not
> even try to look at dev->kobj->dentry.
>
> (It wouldn't be a bad idea to set dev->kobj->dentry to NULL as soon as the
> dentry is deallocated anyway. Doing that would make bugs a little easier
> to spot.)
>
> You know, another possibility is that cdc_acm should call
> tty_unregister_device as soon as the USB device is disconnected. It would
> make sense; no point leaving a tty visible in sysfs if it's no longer
> accessible (except through already-opened file descriptors). However I
> don't know whether the tty subsystem is designed to work that way.
The whole point of having a kref in the device structure is delayed free,
isn't it?
Regards
Oliver
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