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

Pavel Begunkov
2020-07-16T20:48:53Z

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

--
Pavel Begunkov