linux-kernel - Re: [PATCHSET v4 0/5] Add io

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Date:   Tue, 19 Sep 2023 08:57:30 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christian Brauner <brauner@...nel.org>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de, asml.silence@...il.com
Subject: Re: [PATCHSET v4 0/5] Add io_uring support for waitid

On 9/19/23 8:45 AM, Christian Brauner wrote:
> On Tue, Sep 12, 2023 at 11:06:39AM -0600, Jens Axboe wrote:
>> On 9/9/23 9:11 AM, Jens Axboe wrote:
>>> Hi,
>>>
>>> This adds support for IORING_OP_WAITID, which is an async variant of
>>> the waitid(2) syscall. Rather than have a parent need to block waiting
>>> on a child task state change, it can now simply get an async notication
>>> when the requested state change has occured.
>>>
>>> Patches 1..4 are purely prep patches, and should not have functional
>>> changes. They split out parts of do_wait() into __do_wait(), so that
>>> the prepare-to-wait and sleep parts are contained within do_wait().
>>>
>>> Patch 5 adds io_uring support.
>>>
>>> I wrote a few basic tests for this, which can be found in the
>>> 'waitid' branch of liburing:
>>>
>>> https://git.kernel.dk/cgit/liburing/log/?h=waitid
>>>
>>> Also spun a custom kernel for someone to test it, and no issues reported
>>> so far.
>>
>> Forget to mention that I also ran all the ltp testcases for any wait*
>> syscall test, and everything still passes just fine.
> 
> I think the struct that this ends up exposing to io_uring is pretty ugly
> and it would warrant a larger cleanup. I wouldn't be surprised if you
> get some people complain about this.
> 
> Other than that I don't have any complaints about the series.

io_uring only really needs child_wait and wo_pid on the wait_opts side,
for waitid_info it needs all of it. I'm assuming your worry is about the
former rather than the latter.

I think we could only make this smaller if we had a separate entry point
for io_uring, which would then make the code reuse a lot smaller. Right
now we just have __do_wait() abstracted out, and if we added a third
struct that has child_wait/wo_pid and exposed just that, we could not
share this infrastructure.

So as far as I can tell, there's no way to make the sharing less than it
is, at least not without adding cost of more code and less reuse.

Shrug?

-- 
Jens Axboe