Am Donnerstag, den 10.09.2020, 19:01 +0900 schrieb Tetsuo Handa: > On 2020/09/10 18:09, Oliver Neukum wrote: > > > Does it make sense to wait for response of someone else's usb_submit_urb() when > > > someone is calling close(), for there is no guarantee that failure notice received > > > via wdm_flush() via some file descriptor corresponds to usb_submit_urb() request from > > > wdm_write() call from that file descriptor? > > > > Well, user space may do multithreading. Whether it makes sense is > > another question. We just need to return results confirming to the > > standards. You noticed bugs. I think the next version will fix them. > > My question is how do you handle if App1 and App2 (not multithreading but > multiprocessing) shares the "desc" ? Unless Well, device locking is a function of user space. This is Unix. If you have two uncoordinated writers to a device, you cannot expect sensible results. You can expect that the driver does not hang, of course. > > > In patch "[RFC 3/5] CDC-WDM: making flush() interruptible", it is legal to return -EINTR > > > from close(). But I think that returning -EINTR from close() is not recommended because > > > it can confuse multithreaded application (retrying close() upon -EINTR is not safe). > > > > Well, but what is the alternative? Should we ignore signals? > > > > we return the error from write() request (i.e. give up trying to report errors from > close() event), we can't pass results to the intended recipients. That means * harming the single threaded for the sake of the few multithreaded * it would not work for O_NONBLOCK * if you use a device from multiple threads or tasks, locking is your problem Is there something we can do in flush()? Regards Oliver
