netdev - Re: [Bugme-new] [Bug 32832] New: shutdown(2) does not fully shut down socket any more

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Date:	Thu, 14 Apr 2011 10:34:29 +0800
From:	Simon Horman <horms@...ge.net.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, kees@...flux.net
Subject: Re: [Bugme-new] [Bug 32832] New: shutdown(2) does not fully shut
 down socket any more

On Wed, Apr 13, 2011 at 04:55:27AM +0200, Eric Dumazet wrote:
> Le mardi 12 avril 2011 à 16:17 -0700, David Miller a écrit :
> > From: Andrew Morton <akpm@...ux-foundation.org>
> > Date: Tue, 12 Apr 2011 16:15:56 -0700
> > 
> > > 
> > > (switched to email.  Please respond via emailed reply-to-all, not via the
> > > bugzilla web interface).
> > 
> > Stephen Hemminger forwarded this to the list last week, and Eric
> > Dumazet is actively working on a fix.
> 
> I worked on it this week end to discover FreeBSD 8.1 would not allow
> several CLOSE sockets bound to same port even with REUSEADDR.
> 
> So haproxy claim is a bit wrong (its trick doesnt work on FreeBSD), and
> used an undocumented linux feature.
> 
> I feel this case is a call for SO_REUSEPORT, eventually.
> 
> http://www.unixguide.net/network/socketfaq/4.11.shtml
> 
>   SO_REUSEADDR allows your server to bind to an address which is in a
>   TIME_WAIT state.  It does not allow more than one server to bind to
>   the same address.  It was mentioned that use of this flag can create a
>   security risk because another server can bind to a the same port, by
>   binding to a specific address as opposed to INADDR_ANY.  The
>   SO_REUSEPORT flag allows multiple processes to bind to the same
>   address provided all of them use the SO_REUSEPORT option.
> 
> 
> Since SO_REUSEPORT is not a 'stable fix', I suggest we revert the patch,
> and eventually work on SO_REUSEPORT on net-next-2.6
> 
> What do you think ?

Not entirely related, but FWIW I think that SO_REUSEPORT would
be rather useful for haproxy.

I've been working on allowing haproxy to be reconfigured without dropping
or reusing connections. I have done this by re-using open sockets. But it
would have been rather a lot easier to achieve using SO_REUSEPORT -
assuming that I understand SO_REUSEPORT correctly.

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