Re: Sending CQE to a different ring

[Artyom Pavlov <newpavlov@gmail.com>]

>> It looks like we have 3 options:
>> 1) Copy sqe->len to cqe->result without any checks. Disadvantage:
>> user-provided value may collide with EBADFD and EOVERFLOW.
>> 2) Submit error CQE to the submitter ring.
>> 3) Submit error CQE to the receiver ring (cqe->result will contain
>> error code).
> 
> #1 should not be an issue, as cqe->result for those values is the
> original ring result code, not the target ring.
> 
> I'd say the application should just case it to u32 and intepret it like
> that, if it's worried about the signed nature of it?

Ah, indeed. I've missed that EBADFD and EOVERFLOW errors only can happen 
in the submitter ring, so the receiver ring can always interpret CQE 
with the IORING_CQE_F_MSG flag as a successfully received message from 
another ring.