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

[Ming Lei <ming.lei@redhat.com>]

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.

Thanks,
Ming