Re: [PATCH RFC] io_uring: extend io_uring_sqe flags bits

[Jens Axboe <axboe@kernel.dk>]

On 10/31/24 8:42 PM, Ming Lei wrote:
> On Fri, Nov 01, 2024 at 10:12:25AM +0800, Ming Lei wrote:
>> On Thu, Oct 31, 2024 at 03:22:18PM -0600, Jens Axboe wrote:
>>> In hindsight everything is clearer, but it probably should've been known
>>> that 8 bits of ->flags would run out sooner than later. Rather than
>>> gobble up the last bit for a random use case, add a bit that controls
>>> whether or not ->personality is used as a flags2 argument. If that is
>>> the case, then there's a new IOSQE2_PERSONALITY flag that tells io_uring
>>> which personality field to read.
>>>
>>> While this isn't the prettiest, it does allow extending with 15 extra
>>> flags, and retains being able to use personality with any kind of
>>> command. The exception is uring cmd, where personality2 will overlap
>>> with the space set aside for SQE128. If they really need that, then that
>>
>> The space is the 1st `short` for uring_cmd, instead of SQE128 only.
>>
>> Also it is overlapped with ->optval and ->addr3, so just wondering why not
>> use ->__pad2?
>>
>> Another ways is to use __pad2 for sqe2_flags for non-uring_cmd, and for
>> uring_cmd, use its top 16 as sqe2_flags, this way does work, but it is
>> just a bit ugly to use.
> 
> Also IOSQE2_PERSONALITY doesn't have to be per-SQE, and it can be one
> feature of IORING_FEAT_IOSQE2_PERSONALITY, that is why I thought it is
> fine to take the 7th bit as SQE_GROUP now.

Not sure I follow your thinking there, can you expand?

-- 
Jens Axboe