Am Montag, den 12.04.2021, 11:06 -0400 schrieb Alan Stern: > On Mon, Apr 12, 2021 at 11:58:16AM +0200, Oliver Neukum wrote: > > That presumes that the URBs will finish in order. I don't think such > > an assumption can be made. > > I don't understand -- I can't detect any such presumption. OK, this shows that I am bad at explaining. > > As far as I can tell, the only reason for maintaining the URBs in any > particular order on the anchor list is so that usb_kill_anchored_urbs > and usb_poison_anchored_urbs can kill them in reverse order of > submission. THat's why the current code moves completed URBs to the end > of the list. No longer strictly true, as the API has a call to submit everything on an anchor, but I think it boils down to the same thing. > If you keep a pointer to the most recently submitted URB, killing them > easy enough to do. Start with that URB, then go backward through the > list (wrapping to the end when you reach the beginning of the list). Yes, but that supposes that the next on the list has not been resubmitted _before_ the one after it. If you do not keep the list ordered, but in the initial order, we can have the situation that A (happens most recently submitted) is followed by B and C, but C was submitted before B. > > The order in which the URBs complete doesn't matter, because trying to > unlink a completed URB won't cause any harm. As long as it stays completed. > The only assumption here > is that URBs get submitted in the list's order (possibly circularly) -- > this should always be true. I am afraid we cannot guarantee that. It might intuitively seem so, but nothing guarantees that all URBs are going to the same endpoint. Regards Oliver
