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.
Thanks.
