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Date:   Sat, 15 Jul 2023 08:34:55 -0600
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Subject: Re: [PATCH 5/5] io_uring: add IORING_OP_WAITID support
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From:   Jens Axboe <axboe@kernel.dk>
To:     Arnd Bergmann <arnd@arndb.de>,
        Christian Brauner <brauner@kernel.org>
Cc:     io-uring@vger.kernel.org, linux-kernel@vger.kernel.org
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On 7/15/23 8:06?AM, Jens Axboe wrote:
> On 7/15/23 1:12?AM, Arnd Bergmann wrote:
>> On Fri, Jul 14, 2023, at 22:14, Jens Axboe wrote:
>>> On 7/14/23 12:33?PM, Arnd Bergmann wrote:
>>>> On Fri, Jul 14, 2023, at 17:47, Christian Brauner wrote:
>>>>> On Tue, Jul 11, 2023 at 04:18:13PM -0600, Jens Axboe wrote:
>>>>>>>> Does this require argument conversion for compat tasks?
>>>>>>>>
>>>>>>>> Even without the rusage argument, I think the siginfo
>>>>>>>> remains incompatible with 32-bit tasks, unfortunately.
>>>>>>>
>>>>>>> Hmm yes good point, if compat_siginfo and siginfo are different, then it
>>>>>>> does need handling for that. Would be a trivial addition, I'll make that
>>>>>>> change. Thanks Arnd!
>>>>>>
>>>>>> Should be fixed in the current version:
>>>>>>
>>>>>> https://git.kernel.dk/cgit/linux/commit/?h=io_uring-waitid&id=08f3dc9b7cedbd20c0f215f25c9a7814c6c601cc
>>>>>
>>>>> In kernel/signal.c in pidfd_send_signal() we have
>>>>> copy_siginfo_from_user_any() it seems that a similar version
>>>>> copy_siginfo_to_user_any() might be something to consider. We do have
>>>>> copy_siginfo_to_user32() and copy_siginfo_to_user(). But I may lack
>>>>> context why this wouldn't work here.
>>>>
>>>> We could add a copy_siginfo_to_user_any(), but I think open-coding
>>>> it is easier here, since the in_compat_syscall() check does not
>>>> work inside of the io_uring kernel thread, it has to be
>>>> "if (req->ctx->compat)" in order to match the wordsize of the task
>>>> that started the request.
>>>
>>> Yeah, unifying this stuff did cross my mind when adding another one.
>>> Which I think could still be done, you'd just need to pass in a 'compat'
>>> parameter similar to how it's done for iovec importing.
>>>
>>> But if it's ok with everybody I'd rather do that as a cleanup post this.
>>
>> Sure, keeping that separate seem best.
>>
>> Looking at what copy_siginfo_from_user_any() actually does, I don't
>> even think it's worth adapting copy_siginfo_to_user_any() for io_uring,
>> since it's already just a trivial wrapper, and adding another
>> argument would add more complexity overall than it saves.
> 
> Yeah, took a look too this morning, and not sure there's much to reduce
> here that would make it cleaner. I'm going to send out a v2 with this
> unchanged, holler if people disagree.

Looking over changes, none have been made so far. So I guess a v2 can
wait a bit. The branch was rebased to add Christian's acked-bys for some
of the patches, and since a branch it was based on (io_uring-futex) got
rebased to accommodate PeterZ's changes.

-- 
Jens Axboe