kern/179901: [netinet] [patch] Multicast SO_REUSEADDR handled incorrectly

[Mikolaj Golub]

The following reply was made to PR kern/179901; it has been noted by GNATS.

From: Mikolaj Golub <to.my.trociny at gmail.com>
To: Michael Gmelin <freebsd at grem.de>
Cc: Mikolaj Golub <trociny at FreeBSD.org>, bug-followup at FreeBSD.org
Subject: Re: kern/179901: [netinet] [patch] Multicast SO_REUSEADDR handled
 incorrectly
Date: Thu, 27 Jun 2013 23:00:16 +0300

 On Wed, Jun 26, 2013 at 03:03:40PM +0200, Michael Gmelin wrote:
 > Hi,
 > 
 > I adapted the test code, you can find it at
 > 
 > http://blog.grem.de/multicast.c
 > 
 > Test output is:
 > 
 > IPv4 Port 5555:
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv4 Port 5556:
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv4 Port 5557:
 >   Bind using SO_REUSEADDR x 2...OK   (expected)
 >   Bind using SO_REUSEADDR x 2...OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv4 Port 5558:
 >   Bind without socketopts.......OK   (expected)
 >   Bind using SO_REUSEADDR.......FAIL (expected): Address already in use
 >   Bind using SO_REUSEPORT.......FAIL (expected): Address already in use
 > IPv4 Port 5559:
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind without socketopts.......FAIL (expected): Address already in use
 > IPv4 Port 5560:
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind without socketopts.......FAIL (expected): Address already in use
 > IPv6 Port 5555:
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv6 Port 5556:
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv6 Port 5557:
 >   Bind using SO_REUSEADDR x 2...OK   (expected)
 >   Bind using SO_REUSEADDR x 2...OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind using SO_REUSEPORT.......FAIL (NOT expected): Address already in
 > use IPv6 Port 5558:
 >   Bind without socketopts.......OK   (expected)
 >   Bind using SO_REUSEADDR.......FAIL (expected): Address already in use
 >   Bind using SO_REUSEPORT.......FAIL (expected): Address already in use
 > IPv6 Port 5559:
 >   Bind using SO_REUSEADDR.......OK   (expected)
 >   Bind without socketopts.......FAIL (expected): Address already in use
 > IPv6 Port 5560:
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind using SO_REUSEPORT.......OK   (expected)
 >   Bind without socketopts.......FAIL (expected): Address already in use
 > 
 
 Thank you for testing!
 
 > So you maintained the old PORT/ADDR behavior, which I think is not such
 > a great idea. I would suggest to get another opinion on this, just
 > because it's broken now doesn't mean we have to perpetuate it - maybe we
 > should compare the behavior with other Unix(like) OSes like the other
 > BSDs and Linux to see how their implementations work - usually ported
 > software is not changed in that respect, so being compatible is
 > valuable.
 
 It is difficult to talk about portability in the case of SO_REUSEPORT.
 AFAIK, there is no SO_REUSEPORT in Linux and it is recommended to
 always use SO_REUSEADDR for multicast in portable code. It looks like
 in this case we will always have expected behavior with the proposed
 patch.
 
 > Besides my rant the code works as designed and seems to resemble the
 > behavior before r227207 correctly (I manually applied the patches to
 > 9.1-RELEASE).
 > 
 > Fun fact: The code in ip6_output.c could have never worked in the first
 > place, since it used IN_MULTICAST instead of IN6_IS_ADDR_MULTICAST:
 > 
 > if (IN_MULTICAST(ntohl(in6p->inp_laddr.s_addr)))
 > ...
 
 I don't insist on maintaining the old behaviour. But as actually we
 have 2 issues here (regression introduced by me in FreeBSD9 and
 historical behavior that looks wrong), with different priority, I
 would like to fix the issues separately. This way it will be easier to
 track the changes, e.g. when after a year it turns out that the second
 change has broken some other case.
 
 For now I am more concerned about having SO_REUSEADDR regression fixed
 in CURRENT and STABLE9 before 9.2. The patch is under review and I
 plan to commit it next week if it is ok.
 
 The second issue might require more discussion before commiting the
 change.
 
 -- 
 Mikolaj Golub