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

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

[Jens Axboe]

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.

-- 
Jens Axboe

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

io_uring_enter() with opcode IORING_OP_RECV ignores MSG_WAITALL in msg_flags

[Constantine Gavrilov]

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.

-- 
----------------------------------------
Constantine Gavrilov
Storage Architect
Master Inventor
Tel-Aviv IBM Storage Lab
1 Azrieli Center, Tel-Aviv
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