> It would still be a good idea to give drivers an easy way to wait for an
> URB to be completely idle (i.e., completion handler not running and URB
> not currently linked) without making them do careful locking and
Absolutely. That's what people want when they do a synchronous unlink.
> synchronization themselves. To do so would require the core to be able to
> tell, after the completion handler returns, whether the URB has been
> resubmitted. Currently I don't think there is any way to do this.
It is doable with a flag. Set it in usb_submit_urb() and reset
it in usb_urb_giveback_urb(). As we have established usb_urb_giveback_urb()
cannot be reentered, so I see no race in checking that flag after the
completion handler.
The code have already proposed should in essence be up to it.
> > Hm, I am unsure.
> > Couldn't we eliminate most uses of usb_unlink_urb() from 2.6 anyway?
>
> A lot of them, probably yes. However there must be cases where drivers
> want to unlink an URB because of a timeout rather than disconnection.
> usb-storage does that, but it always uses async unlinking.
In the network drivers. But they also use asynchronous unlink iirc.
Regards
Oliver
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