linux-kernel - Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for io_uring

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Message-ID: <0357e544-d534-06d2-dc61-1169fc172d20@kernel.dk>
Date:   Thu, 16 Jul 2020 15:20:53 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Stefano Garzarella <sgarzare@...hat.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kees Cook <keescook@...omium.org>,
        Aleksa Sarai <asarai@...e.de>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Jann Horn <jannh@...gle.com>, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for
 io_uring_register(2) opcodes

On 7/16/20 2:51 PM, Jens Axboe wrote:
> On 7/16/20 2:47 PM, Pavel Begunkov wrote:
>> On 16/07/2020 23:42, Jens Axboe wrote:
>>> On 7/16/20 2:16 PM, Pavel Begunkov wrote:
>>>> On 16/07/2020 15:48, Stefano Garzarella wrote:
>>>>> The enumeration allows us to keep track of the last
>>>>> io_uring_register(2) opcode available.
>>>>>
>>>>> Behaviour and opcodes names don't change.
>>>>>
>>>>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>>>>> ---
>>>>>  include/uapi/linux/io_uring.h | 27 ++++++++++++++++-----------
>>>>>  1 file changed, 16 insertions(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
>>>>> index 7843742b8b74..efc50bd0af34 100644
>>>>> --- a/include/uapi/linux/io_uring.h
>>>>> +++ b/include/uapi/linux/io_uring.h
>>>>> @@ -253,17 +253,22 @@ struct io_uring_params {
>>>>>  /*
>>>>>   * io_uring_register(2) opcodes and arguments
>>>>>   */
>>>>> -#define IORING_REGISTER_BUFFERS		0
>>>>> -#define IORING_UNREGISTER_BUFFERS	1
>>>>> -#define IORING_REGISTER_FILES		2
>>>>> -#define IORING_UNREGISTER_FILES		3
>>>>> -#define IORING_REGISTER_EVENTFD		4
>>>>> -#define IORING_UNREGISTER_EVENTFD	5
>>>>> -#define IORING_REGISTER_FILES_UPDATE	6
>>>>> -#define IORING_REGISTER_EVENTFD_ASYNC	7
>>>>> -#define IORING_REGISTER_PROBE		8
>>>>> -#define IORING_REGISTER_PERSONALITY	9
>>>>> -#define IORING_UNREGISTER_PERSONALITY	10
>>>>> +enum {
>>>>> +	IORING_REGISTER_BUFFERS,
>>>>> +	IORING_UNREGISTER_BUFFERS,
>>>>> +	IORING_REGISTER_FILES,
>>>>> +	IORING_UNREGISTER_FILES,
>>>>> +	IORING_REGISTER_EVENTFD,
>>>>> +	IORING_UNREGISTER_EVENTFD,
>>>>> +	IORING_REGISTER_FILES_UPDATE,
>>>>> +	IORING_REGISTER_EVENTFD_ASYNC,
>>>>> +	IORING_REGISTER_PROBE,
>>>>> +	IORING_REGISTER_PERSONALITY,
>>>>> +	IORING_UNREGISTER_PERSONALITY,
>>>>> +
>>>>> +	/* this goes last */
>>>>> +	IORING_REGISTER_LAST
>>>>> +};
>>>>
>>>> It breaks userspace API. E.g.
>>>>
>>>> #ifdef IORING_REGISTER_BUFFERS
>>>
>>> It can, yes, but we have done that in the past. In this one, for
>>
>> Ok, if nobody on the userspace side cares, then better to do that
>> sooner than later.

I actually don't think it's a huge issue. Normally if applications
do this, it's because they are using it and need it. Ala:

#ifndef IORING_REGISTER_SOMETHING
#define IORING_REGISTER_SOMETHING	fooval
#endif

and that'll still work just fine, even if an identical enum is there.

-- 
Jens Axboe