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

[Pavel Begunkov <asml.silence@gmail.com>]

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