On Thu, 7 Jun 2012, Stefani Seibold wrote: > Am Donnerstag, den 07.06.2012, 10:28 -0400 schrieb Alan Stern: > > On Thu, 7 Jun 2012, Stefani Seibold wrote: > > > > > I tried to implement your idea to kick away the usb_device pointer, but > > > i think it is impossible. The skel_delete() function needs the > > > usb_device pointer for calling usb_put, which is called from > > > skel_disconnect() or skel_release(). > > > > Does skel_delete() really need to call usb_put_dev()? I suspect that > > the driver doesn't need to take a reference to either the device or the > > interface. > > > > I think it will be needed, since usb core will decrement the reference > when the device go away. But before it decrements the reference, it will unbind the driver. As long as usb-skeleton is careful not to access the device or the interface after the disconnect routine returns, it doesn't need to keep a reference. > Lock every access to the usb core if a tedious > thing and will waste a lot of code. With proper design, it's not necessary to lock every access. > The problem with hotpluging is not the plug, it is the unplug, which can > happen any time. > > BTW: An interface have no reference count. Sure it does. Look at the definitions of usb_get_intf() and usb_put_intf() in drivers/usb/core/usb.c. > > If skel_delete is changed then we don't need the usb_device pointer. > > > > I have no idea how to do this. Every USB driver i know stores the > usb_device pointer. > > Maybe you have an idea? No, I was wrong. It turns out we really do need to keep the udev pointer, because it gets used in calls to usb_fill_bulk_urb(). However there's nothing wrong with keeping pointers to both the device and the interface, if there's a good reason for doing so. (It also gets used in calls to usb_alloc_coherent(), but I would prefer to get rid of the coherent buffers. They are rarely useful and don't belong here.) Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
