> On 28. Feb 2020, at 15:31, Xin Long <lucien.xin@xxxxxxxxx> wrote:
>
> On Fri, Feb 28, 2020 at 9:57 PM Leppanen, Jere (Nokia - FI/Espoo)
> <jere.leppanen@xxxxxxxxx> wrote:
>>
>> On Thu, 27 Feb 2020, Xin Long wrote:
>>
>>> On Tue, Feb 25, 2020 at 3:28 AM Leppanen, Jere (Nokia - FI/Espoo)
>>> <jere.leppanen@xxxxxxxxx> wrote:
>>>>
>>>> On Sat, 22 Feb 2020, Xin Long wrote:
>>>>
>>>>> On Thu, Feb 20, 2020 at 5:18 PM Leppanen, Jere (Nokia - FI/Espoo)
>>>>> <jere.leppanen@xxxxxxxxx> wrote:
>>>>>>
>>>>>> Hello All,
>>>>>>
>>>>>> According to the RFC, a peeled-off socket is a one-to-one socket. But
>>>>>> in lksctp a peeled-off socket it not TCP style, it's UDP_HIGH_BANDWIDTH
>>>>>> style. Because of this, shutdown() doesn't work, linger probably
>>>>>> doesn't work, and so on.
>>>>>>
>>>>>> For example, in sctp_shutdown():
>>>>>>
>>>>>> static void sctp_shutdown(struct sock *sk, int how)
>>>>>> {
>>>>>> struct net *net = sock_net(sk);
>>>>>> struct sctp_endpoint *ep;
>>>>>>
>>>>>> if (!sctp_style(sk, TCP))
>>>>>> return;
>>>>>>
>>>>>> Here we just bail out, because a peeled-off socket is not TCP style.
>>>>>>
>>>>>> Is this just a bug, or am I missing something? Asking mostly out of
>>>>>> personal curiosity.
>>>>> I would say, it's because .shutdown is tcp_prot thing and udp_prot doesn't
>>>>> have. sctp doesn't have to implement it for UDP style socket. But for TCP-
>>>>> style socket, sctp is trying to be compatible with TCP protocol user API.
>>>>> But even though, sctp's .shutdown is still not fully compatible with TCP
>>>>> protocol due to sctp's 3-way shakehands for finishing a connection.
>>>>
>>>> Thanks a bunch for replying, Xin Long. I'm not quite sure what you mean.
>>>> The actual association shutdown doesn't even come into play here, since
>>>> shutdown() doesn't do anything with peeled-off sockets.
>>> Hi, Leppanen,
>>> sorry for late.
>>>
>>> SCTP has two types of sockets: UDP and TCP styles.
>>> TCP style associations are not allowed to be peeled off.
>>> only UDP style associations can be peeled off.
>>>
>>> Then shutdown can only work for TCP style, this explains
>>> why peeled-off sk can use shutdown.
>>>
>>>
>>>>
>>>> If you mean that the current implementation of shutdown() might have
>>>> some problems with peeled-off sockets; well, that's true, but I suppose
>>>> that means that there's something to fix somewhere.
>>> I think it returns for peeled-off sockets (UDP style sockets) on purpose.
>>> it's like why you want to use shutdown on a UDP socket?
>>>
>>>>
>>>> It looks like the reason for the peculiar socket style of peeled-off
>>>> sockets is that they're created by copying from a one-to-many socket and
>>>> modified a little to resemble a one-to-one socket. But this leads to
>>>> problems in several places in the code. Is this just implementation that
>>>> was never finalized?
>>> Right, peeled-off will allow users to use a new sk to control that asoc.
>>> but again, it's a feature UDP style socket.
>>> any other problems have you seen?
>>
>> To clarify, by "peeled-off socket" I mean a socket returned by
>> sctp_peeloff(). sctp_peeloff() takes as an argument a
>> one-to-many socket, and returns a one-to-one socket.
>>
>> The RFC (https://tools.ietf.org/html/rfc6458#section-9.2)
>> clearly states about the socket returned by sctp_peeloff() that
>> "[...] the new socket is a one-to-one style socket."
> OK, I got you now.
> Linux creates a TCP/one-to-many style socket there actually.
> Interesting, BSD seems to do the same.
> I will double check and make a patch for this once confirmed.
I would expect that the socket returned by sctp_peeloff() is
a one-to-one style socket and behave like one. If BSD is not
like this, it is a bug and I would like to know.
Best regards
Michael
>
> Thanks.
