> On Aug 26, 2020, at 12:26 PM, Josef <josef.grieb@xxxxxxxxx> wrote: > > 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 The user_data is *always* passed straight from the sqe, so it is set to whatever you put in there. That’s a key component of the protocol, allowing you to tie a completion event back to your submission. And also allows you to do a directed cancel event for a given pending request.
