On 11/4/20 7:50 AM, Jens Axboe wrote:
> On 11/4/20 4:21 AM, Stefan Metzmacher wrote:
>> Hi David,
>>
>>> New to io_uring but can't find this answer online, so reaching out.
>>>
>>> I was trying out io_uring with netperf - tcp stream sockets - and
>>> noticed a submission is called complete even with a partial send
>>> (io_send(), ret < sr->len). Saving the offset of what succeeded (plus
>>> some other adjustments) and retrying the sqe again solves the problem.
>>> But the issue seems fundamental so wondering if is intentional?
>>
>> I guess this is just the way it is currently.
>>
>> For Samba I'd also like to be sure to never get short write to a socket.
>>
>> There I'd like to keep the pipeline full by submitting as much sqe's as possible
>> (without waiting for completions on every single IORING_OP_SENDMSG/IORING_OP_SPLICE)
>> using IOSQE_IO_DRAIN or IOSQE_IO_LINK and maybe IOSQE_ASYNC or IORING_SETUP_SQPOLL.
>>
>> But for now I just used a single sqe with IOSQE_ASYNC at a time.
>>
>> Jens, do you see a way to overcome that limitation?
>>
>> As far as I understand the situation is completely fixed now and
>> it's no possible to get short reads and writes for file io anymore, is that correct?
> 
> Right, the regular file IO will not return short reads or writes, unless a
> blocking attempt returns 0 (or short). Which would be expected. The send/recvmsg
> side just returns what the socket read/write would return, similarly to if you
> did the normal system call variants of those calls.
> 
> It would not be impossible to make recvmsg/sendmsg handle this internally as
> well, we just need a good way to indicate the intent of "please satisfy the
> whole thing before return".
> 

Attached patch handles the full send request; sendmsg can be handled
similarly.

I take your comment to mean there should be an sq flag to opt-in to the
behavior change? Pointers to which flag set?