linux-kernel - Re: [PATCH 0/2] uring

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Message-ID: <d7496fbf-ccec-4b38-81da-8b5674993b15@gmail.com>
Date: Thu, 13 Feb 2025 16:11:08 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Caleb Sander Mateos <csander@...estorage.com>,
 Keith Busch <kbusch@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Riley Thomasson <riley@...estorage.com>,
 io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] uring_cmd SQE corruptions

On 2/12/25 23:46, Caleb Sander Mateos wrote:
> On Wed, Feb 12, 2025 at 3:21 PM Keith Busch <kbusch@...nel.org> wrote:
>>
>> On Wed, Feb 12, 2025 at 03:07:30PM -0800, Caleb Sander Mateos wrote:
>>>
>>> Yes, we completely agree. We are working on incorporating Keith's
>>> patchset now. It looks like there is still an open question about
>>> whether userspace will need to enforce ordering between the requests
>>> (either using linked operations or waiting for completions before
>>> submitting the subsequent operations).
>>
>> In its current form, my series depends on you *not* using linked
>> requests. I didn't think it would be a problem as it follows an existing
>> pattern from the IORING_OP_FILES_UPDATE operation. That has to complete
>> in its entirety before prepping any subsequent commands that reference
>> the index, and using links would get the wrong results.
> 
> As implementers of a ublk server, we would also prefer the current
> interface in your patch series! Having to explicitly order the
> requests would definitely make the interface more cumbersome and
> probably less performant. I was just saying that Ming and Pavel had
> raised some concerns about guaranteeing the order in which io_uring
> issues SQEs. IORING_OP_FILES_UPDATE is a good analogy. Do we have any
> examples of how applications use it? Are they waiting for a
> completion, linking it, or relying on io_uring to issue it
> synchronously?

With files you either handle it in user space by waiting for
completion or link them. The difference with buffers is that
linking wouldn't currently work for buffers, but we can change
that.

-- 
Pavel Begunkov