Jens Axboe <axboe@xxxxxxxxx> writes: > The application currently has no way of knowing if a given opcode is > supported or not without having to try and issue one and see if we get > -EINVAL or not. And even this approach is fraught with peril, as maybe > we're getting -EINVAL due to some fields being missing, or maybe it's > just not that easy to issue that particular command without doing some > other leg work in terms of setup first. > > This adds IORING_REGISTER_PROBE, which fills in a structure with info > on what it supported or not. This will work even with sparse opcode > fields, which may happen in the future or even today if someone > backports specific features to older kernels. This looks pretty good to me. You can call it with 0 args to get the total number of ops, then allocate an array with that number and re-issue the syscall. I also like that you've allowed for backporting subsets of functionality. I have one question below: > @@ -6632,6 +6674,12 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode, > break; > ret = io_eventfd_unregister(ctx); > break; > + case IORING_REGISTER_PROBE: > + ret = -EINVAL; > + if (!arg || nr_args > 256) > + break; > + ret = io_probe(ctx, arg, nr_args); > + break; Why 256? If it's just arbitrary, please add a comment. Otherwise looks good! Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
