On 11/1/24 9:01 AM, Ming Lei wrote: > On Fri, Nov 01, 2024 at 08:42:42AM -0600, Jens Axboe wrote: >> On 11/1/24 8:34 AM, Ming Lei wrote: >>> On Fri, Nov 01, 2024 at 07:59:38AM -0600, Jens Axboe wrote: >>>> 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? >>> >>> It could be one io_uring setup flag, such as >>> IORING_SETUP_IOSQE2_PERSONALITY. >>> >>> If this flag is set, take __pad2 as sqe2_flags, otherwise use current >>> way, so it doesn't have to take bit7 of sqe_flags for this purpose. >> >> Would probably have to be a IORING_SETUP_IOSQE2_FLAGS or something in >> general. And while that could work, not a huge fan of that. I think we >> should retain that for when a v2 of the sqe is done, to coordinate which >> version to use. > > Fair enough. > > Now there are 16bits for new features, which may put v2 off long enough. Exactly, hopefully that'll push the need out quite a bit, so we have time to do something nice for v2. >>> Also in future, if uring_cmd needs personality, it still may reuse top >>> 16bit of uring_cmd_flags for that. >> >> Right, that's what I referred to in terms of uring_cmd just having its >> own way to set personality. > > Then this approach is safe to go, imo. Thanks I think so too, and it'll unblock the sqe grouping. So at least that paves the way for the first part of your patchset. I'll post a v2 of it shortly. -- Jens Axboe
