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

[Jens Axboe <axboe@kernel.dk>]

On 11/1/24 10:59 AM, Pavel Begunkov wrote:
> On 10/31/24 21:22, 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
>> would have to be done via a uring cmd flag.
> 
> Interesting, I was just experimenting using the personality bits for
> similar purposes I mentioned but in a different way, and I even thought
> if anything it could be used to extend sqe flags though I'm not a huge
> fan of that.

We're going to need more SQE flags at some point. At least with the
potential to extend it with a setup flag in the future, we can grab the
last one and have that other option down the line.

I don't mind grabbing personality. Obviously it'd be better to get free
space somewhere, but there's no free real estate...

-- 
Jens Axboe