On Wed, 26 Aug 2020 at 15:44, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 8/25/20 9:01 PM, Josef wrote: > >> In order for the patch to be able to move ahead, we'd need to be able > >> to control this behavior. Right now we rely on the file being there if > >> we need to repoll, see: > >> > >> commit a6ba632d2c249a4390289727c07b8b55eb02a41d > >> Author: Jens Axboe <axboe@xxxxxxxxx> > >> Date: Fri Apr 3 11:10:14 2020 -0600 > >> > >> io_uring: retry poll if we got woken with non-matching mask > >> > >> If this never happened, we would not need the file at all and we could > >> make it the default behavior. But don't think that's solvable. > >> > >>> is there no other way around to close the file descriptor? Even if I > >>> remove the poll, it doesn't work > >> > >> If you remove the poll it should definitely work, as nobody is holding a > >> reference to it as you have nothing else in flight. Can you clarify what > >> you mean here? > >> > >> I don't think there's another way, outside of having a poll (io_uring > >> or poll(2), doesn't matter, the behavior is the same) being triggered in > >> error. That doesn't happen, as mentioned if you do epoll/poll on a file > >> and you close it, it won't trigger an event. > >> > >>> btw if understood correctly poll remove operation refers to all file > >>> descriptors which arming a poll in the ring buffer right? > >>> Is there a way to cancel a specific file descriptor poll? > >> > >> You can cancel specific requests by identifying them with their > >> ->user_data. You can cancel a poll either with POLL_REMOVE or > >> ASYNC_CANCEL, either one will find it. So as long as you have that, and > >> it's unique, it'll only cancel that one specific request. > > > > thanks it works, my bad, I was not aware that user_data is associated > > with the poll request user_data...just need to remove my server socket > > poll which binds to an address so I think this patch is not really > > necessary > > > > btw IORING_FEAT_FAST_POLL feature which arming poll for read events, > > how does it work when the file descriptor(not readable yet) wants to > > read(non blocking) something and I close(2) the file descriptor? I'm > > guessing io_uring doesn't hold any reference to it anymore right? > > Most file types will *not* notify you through poll if they get closed, > so it'll just sit there until canceled. This is the same with poll(2) or > epoll(2). io_uring will continue to hold a reference to the file, it > does that over request completion for any request that uses a file. okay, btw according to the man page IORING_OP_POLL_REMOVE it's unclear to me what value user_data contains in the cqe I'm guessing user_data is always 0 right? just tested it with liburing I got always 0(user_data) even if there is no polling request --- Josef Grieb
