Re: recvmsg not honoring O_NONBLOCK

[Jens Axboe <axboe@kernel.dk>]

On 7/9/22 8:21 AM, Hrvoje Zeba wrote:
> Hi folks,
> 
> I was adapting msquic library to work with iouring and found an issue
> with recvmsg() where it ignores O_NONBLOCK flag set on the file
> descriptor. If MSG_DONTWAIT is set in flags, it behaves as expected.
> I've attached a simple test which currently just hangs on iouring's
> recvmsg(). I'm guessing sendmsg() behaves the same way but I have no
> idea how to fill the buffer to reliably test it.

I am guessing that you're waiting off waiting for the event. It's not
stalled on the issue, it'll arm poll and wait for an event. I won't go
into too much of a ran on O_NONBLOCK, but it's a giant mess, and where
possible, io_uring relies on per-request non-block flags as that is much
saner behavior.

-- 
Jens Axboe