Re: Zoned storage and BLK_STS_RESOURCE

[Jens Axboe <axboe@kernel.dk>]

> Of note about io_uring: if writes are submitted from multiple jobs to
> multiple queues, then you will see unaligned write errors, but the
> same test with libaio will work just fine. The reason is that io_uring
> fio engine IO submission only adds write requests to the io rings,
> which will then be submitted by the kernel ring handling later. But at
> that time, the ordering information is lost and if the rings are
> processed in the wrong order, you'll get unaligned errors.

Sorry, but this is woefully incorrect.

Submissions are always in order, I suspect the main difference here is
that some submissions would block, and that will certainly cause the
effective issue point to be reordered, as the initial issue will get
-EAGAIN. This isn't a problem on libaio as it simply blocks on
submission instead. Because the actual issue is the same, and the kernel
will absolutely see the submissions in order when io_uring_enter() is
called, just like it would when io_submit() is called.

If you stay within the queue limits of the device, then there should be
no reordering. Unless the kernel side prevents non-blocking issues for
some reason.

It's either that, or something being broken with REQ_NOWAIT handling for
zoned writes.

-- 
Jens Axboe