Re: [PATCH 10/11] contrib: Add program to document and test assumptions about SO_REUSEADDR

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Jul 05, 2024 at 10:33:43AM +0200, Stefano Brivio wrote:
> On Fri, 5 Jul 2024 10:06:12 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Thu, Jul 04, 2024 at 11:21:21PM +0200, Stefano Brivio wrote:
> > > On Thu,  4 Jul 2024 14:58:34 +1000
> > > David Gibson <david@gibson.dropbear.id.au> wrote:
> > >   
> > > > For the approach we intend to use for handling UDP flows, we have some
> > > > pretty specific requirements about how SO_REUSEADDR works with UDP sockets.
> > > > Specifically SO_REUSEADDR allows multiple sockets with overlapping bind()s,
> > > > and therefore there can be multiple sockets which are eligible to receive
> > > > the same datagram.  Which one will actually receive it is important to us.
> > > > 
> > > > Add a test program which verifies things work the way we expect, which
> > > > documents what those expectations are in the process.
> > > > 
> > > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > > > ---
> > > >  contrib/udp-behaviour/.gitignore           |   1 +
> > > >  contrib/udp-behaviour/Makefile             |  45 ++++
> > > >  contrib/udp-behaviour/common.c             |  66 ++++++
> > > >  contrib/udp-behaviour/common.h             |  47 ++++
> > > >  contrib/udp-behaviour/reuseaddr-priority.c | 240 +++++++++++++++++++++
> > > >  5 files changed, 399 insertions(+)  
> > > 
> > > I reviewed these (10/11 and 11/11) a bit lightly, but they look sane to
> > > me. I just wonder: wouldn't it be better to have
> > > contrib/linux/udp-behaviour instead, so that it's consistent with the
> > > other stuff unter contrib/ (project names, kind of)?  
> > 
> > Well.. if we ever port to something non-Linux, we'll need the same
> > socket behaviour there.  Indeed, that's one reason I think having
> > these test programs is valuable.  So I don't think 'linux/' is a great
> > pick.
> 
> Oh, oops, I thought SO_REUSEADDR were specific to Linux, that's why I
> was suggesting linux/, but it's actually supported by all the BSDs.

RIght.  I believe SO_REUSEPORT is Linux specific, but the weaker
SO_REUSEADDR is much older, and is all I need for the things I have
planned.

> > In some ways contrib/ isn't really the right place for this.  Maybe
> > it would be better under doc/?  But at the moment that's more user
> > facing than developer facing documentation.
> 
> I would still say it's documentation and it can happily fit under doc/.
> Distribution packages don't copy the whole doc/ (to /usr/share/doc/)
> anyway.

Ok, I'm going with doc/platform-requirements/ in the next spin.
> 
> Or test/kernel/? But it's not something we want to check regularly,
> it's really an example to help with development.
> 
> All in all, I don't have a strong preference, doc/ looks like a better
> fit to me, but contrib/ isn't problematic either.
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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