Re: Review of gnio, round 1
- From: Alexander Larsson <alexl redhat com>
- To: Dan Winship <danw gnome org>
- Cc: Ryan Lortie <desrt desrt ca>, gtk-devel-list <gtk-devel-list gnome org>, gicmo gnome org
- Subject: Re: Review of gnio, round 1
- Date: Mon, 27 Apr 2009 22:20:02 +0200
On Mon, 2009-04-27 at 11:55 -0400, Dan Winship wrote:
> Ryan Lortie wrote:
> > Not sure I agree. See shutdown() syscall. The fact that this call
> > exists means that the designers of [unix or tcp or whatever] went out of
> > their way because they disagreed with you.
> I can't think of any time I've used SHUT_RD or SHUT_WR rather than
> SHUT_RDWR though...
You can use SHUT_WR to get reliable socket shutdown, making sure the
remote side got all the data (without using SO_LINGER). See e.g.:
Although this kind of thing looks like something the highlevel code
should support not by exposing shutdown, but rather by having a function
that does all of this.
> >> Furthermore, its actually a problem in the ipv4 vs ipv6 magic case. The
> >> current tcplistener code first tries to do an ipv6 socket and only if
> >> that fails it tries an ipv4 socket. This makes sense on linux, were an
> >> ipv6 socket also can accept ipv4 connections. However, this is not true
> >> on many other unixes, where you need two sockets to handle both ipv4 and
> >> ipv6. So in this case the listener object actually gets in the way, as
> >> we'd need to create two listener objects to handle this (or make the
> >> listener have two sockets).
> > The 4-over-6 functionality (and even the setsockopt to disable it) is
> > specified in some RFC somewhere.
> Right, but it's disabled (at the kernel level) by default on most OSes
> (everything but Linux?) because apparently the behavior is
> underspecified. (Eg, see
> So to avoid separate Linux-vs-everyone-else codepaths, it's probably
> best to use IPV6_V6ONLY and manage v4 and v6 sockets separately everywhere.
As per http://people.redhat.com/drepper/userapi-ipv6.html this doesn't
work for linux, as it only allows one socket per port. Isn't portable
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