Re: [PATCH v4 1/2] fs/aio: Restrict kiocb_set_cancel_fn() to I/O submitted via libaio

[Bart Van Assche <bvanassche@acm.org>]

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
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? The AIO code
supports cancelling I/O after call_read_iter() or call_write_iter() has
been called.

Thanks,

Bart.