On 3/5/24 1:43 PM, Bart Van Assche wrote: > On 3/4/24 12:21, Jens Axboe wrote: >> On 3/4/24 12:43 PM, Bart Van Assche wrote: >>> As far as I know no Linux user space interface for submitting I/O >>> supports cancellation of read or write requests other than the AIO >>> io_cancel() system call. >> >> Not true, see previous reply (on both points in this email). The kernel >> in general does not support cancelation of regular file/storage IO that >> has submitted. That includes aio. There are many reasons for this. >> >> For anything but that, you can most certainly cancel inflight IO with >> io_uring, be it to a socket, pipe, whatever. >> >> The problem here isn't that only aio supports cancelations, it's that >> the code to do so is a bad hack. > > What I meant is that the AIO code is the only code I know of that > supports cancelling I/O from user space after the I/O has been submitted > to the driver that will process the I/O request (e.g. a USB driver). Is Right, we never offered that in general in the kernel. Like I said, it's just a hack what is there for that. > my understanding correct that io_uring cancellation involves setting the > IO_WQ_WORK_CANCEL flag and also that that flag is ignored by > io_wq_submit_work() after io_assign_file() has been called? No, that's only for requests that go via io-wq, which is generally not the fast path and most workloads will never see that. For anything else, cancelation can very much happen at any time. > The AIO code > supports cancelling I/O after call_read_iter() or call_write_iter() has > been called. ...for the above hacky case, and that's it, not as a generic thing. -- Jens Axboe
