On Tue, 7 Oct 2014, Michal Nazarewicz wrote: > > On Tue, 7 Oct 2014, Felipe Balbi wrote: > >> Right, but if we allow this, I can already see folks abusing to > >> connect to the host early and only when necessary do some trickery to > >> e.g. start adbd (not saying Android will do this, just using it as an > >> easy example). > > I don't really see that happening. For the gadget to start all > descriptors need to be known. Functionfs will know the descriptors > only once the user space daemon provides them. Therefore, with the > current features (or even with addition of Robert's feature) there is no > way to let the gadget start without having the daemon running. > > On Tue, Oct 07 2014, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > We can still keep the pullup turned off until all the functions are > > ready. That's a part of normal behavior -- unlike what happens when a > > userspace component crashes or is killed. > > >> Then how do we differentiate a normal close() from a "oh-crap-I-died" > >> close() ? > > > We can't, so why worry about it? > > We actually might be able to distinguish those cases with another ioctl > which daemon must issue on the ep0 prior to closing it. I'm not saying > that we should implement that though. > > > If a file handle was closed for normal reasons then userspace probably > > in the middle of shutting down the gadget anyway. If not then the > > user will get what they deserve. > > > > If the file handle was closed for abnormal reasons, we can behave like > > crashed firmware. Which means, in the end, doing the same thing as in > > the normal-reason case -- i.e., do nothing. In particular, don't > > disconnect. > > > > If you want to allow for the possibility of orderly shutdown (and maybe > > even possible restart) of a userspace handler, the function library > > should first tell the kernel explicitly to disconnect. Then function > > components can be changed around completely, and when everything is > > ready, userspace can tell the kernel to connect again. > > I'm wondering if it would be possible to support user-space daemon > restarts with O_APPEND flag. This is probably looking too far to the > future though. Actually, we shouldn't need to consider the case where the descriptors change. That _always_ requires a disconnect, and the user can cause a disconnect simply by killing the daemon and starting it again. No separate restart capability is needed. 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
