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."
