Re: io_uring_enter() with opcode IORING_OP_RECV ignores MSG_WAITALL in msg_flags

[Pavel Begunkov]

On 3/23/22 12:19, Jens Axboe wrote:
> On 3/23/22 4:31 AM, Constantine Gavrilov wrote:
> > I get partial receives on TCP socket, even though I specify
> > MSG_WAITALL with IORING_OP_RECV opcode. Looking at tcpdump in
> > wireshark, I see entire reassambled packet (+4k), so it is not a
> > disconnect. The MTU is smaller than 4k.
> >
> >  From the mailing list history, looks like this was discussed before
> > and it seems the fix was supposed to be in. Can someone clarify the
> > expected behavior?
> >
> > I do not think rsvmsg() has this issue.
>
> Do you have a test case? I added the io-uring list, that's the
> appropriate forum for this kind of discussion.

MSG_WAITALL (since Linux 2.2)
       This flag requests that the operation block until the full
       request is satisfied.  However, the call may still return
       less data than requested if a signal is caught

My guess would be that it's either due to signals (including
task_works actively used by io_uring) or because of some
interoperability problem with NOWAIT.

--
Pavel Begunkov