Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for io_uring_register(2) opcodes

Jens Axboe
2020-07-16T20:51:34Z

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@redhat.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.
>
>
>> example:
>>
>> commit 9e3aa61ae3e01ce1ce6361a41ef725e1f4d1d2bf (tag: io_uring-5.5-20191212)
>> Author: Jens Axboe <axboe@kernel.dk>
>> Date: Wed Dec 11 15:55:43 2019 -0700
>>
>> io_uring: ensure we return -EINVAL on unknown opcod
>>
>> But it would be safer/saner to do this like we have the done the IOSQE_
>> flags.
>
> IOSQE_ are a bitmask, but this would look peculiar
>
> enum {
> __IORING_REGISTER_BUFFERS,
> ...
> };
> define IORING_REGISTER_BUFFERS __IORING_REGISTER_BUFFERS

Yeah true of course, that won't really work for this case at all.

That said, I don't think it's a huge deal to turn it into an enum.

--
Jens Axboe