On 4/30/20 10:14 PM, Jens Axboe wrote: > On 4/30/20 9:58 PM, Al Viro wrote: >> On Thu, Apr 30, 2020 at 10:24:46AM -0600, Jens Axboe wrote: >>> Pipe read/write only checks for the file O_NONBLOCK flag, but we should >>> also check for IOCB_NOWAIT for whether or not we should handle this read >>> or write in a non-blocking fashion. If we don't, then we will block on >>> data or space for iocbs that explicitly asked for non-blocking >>> operation. This messes up callers that explicitly ask for non-blocking >>> operations. >> >> Why does io_uring allow setting IOCB_NOWAIT without FMODE_NOWAIT, anyway? > > To do per-io non-blocking operations. It's not practical or convenient > to flip the file flag, nor does it work if you have multiple of them > going. If pipes honor the flag for the read/write iter handlers, then > we can handle them a lot more efficiently instead of requiring async > offload. Sorry, I think I misread you and the answer, while correct by itself, is not the answer to the question you are asking. You're saying we should not be using IOCB_NOWAIT if FMODE_NOWAIT isn't set, which is fair. I'll re-do the patch, we can probably just use FMODE_NOWAIT for the final check in io_uring instead. For pipes, we should include the setting of FMODE_NOWAIT for fifo_open() with the patch, at least. -- Jens Axboe
