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

Jens Axboe
2020-07-16T20:42:12Z

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
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.

--
Jens Axboe