[libvirt] [PATCH] loopback is not always just lo

[Roman Bogorodskiy]

  Pino Toscano wrote:

> On Monday, 7 November 2016 13:10:06 CET Laine Stump wrote:
> > On 11/07/2016 04:15 AM, Daniel P. Berrange wrote:
> > > On Mon, Nov 07, 2016 at 01:52:05AM -0500, Laine Stump wrote:
> > >> On 11/06/2016 01:54 AM, Roman Bogorodskiy wrote:
> > >>>     Daniel P. Berrange wrote:
> > >>>
> > >>>> On Tue, Nov 01, 2016 at 06:15:59PM +0300, Pavel Timofeev wrote:
> > >>>>>    On BSD family OSes (Free/Net/Open/DragonFlyBSD, Mac OS) and
> > >>>>>    Solaris loopback interface is called 'lo0' instead of just 'lo'.
> > >>>>>
> > >>>>> ---
> > >>>>>    src/network/bridge_driver.c | 5 +++++
> > >>>>>    1 file changed, 5 insertions(+)
> > >>>>>
> > >>>>> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
> > >>>>> index a3ee3f3..9d94d65 100644
> > >>>>> --- a/src/network/bridge_driver.c
> > >>>>> +++ b/src/network/bridge_driver.c
> > >>>>> @@ -1002,7 +1002,12 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
> > >>>>>            virBufferAsprintf(&configbuf, "pid-file=%s\n", pidfile);
> > >>>>>        /* dnsmasq will *always* listen on localhost unless told otherwise */
> > >>>>> +#ifdef __linux__
> > >>>>>        virBufferAddLit(&configbuf, "except-interface=lo\n");
> > >>>>> +#else
> > >>>>> +    /* BSD family OSes and Solaris call loopback interface as lo0 */
> > >>>>> +    virBufferAddLit(&configbuf, "except-interface=lo0\n");
> > >>>>> +#endif
> > >>>>>        if (dnsmasqCapsGet(caps, DNSMASQ_CAPS_BIND_DYNAMIC)) {
> > >>>>>            /* using --bind-dynamic with only --interface (no
> > >>>> ACK will push shortly.
> > >>> This breaks all the networkxml2conftest tests, for example:
> > >>>
> > >>> $ VIR_TEST_DEBUG=1 VIR_TEST_RANGE=1 ./tests/networkxml2conftest
> > >>> TEST: networkxml2conftest
> > >>>    1) Network XML-2-Conf isolated-network                               ...
> > >>> In '/home/novel/code/libvirt/tests/networkxml2confdata/isolated-network.conf':
> > >>> Offset 303
> > >>> Expect [
> > >>> ]
> > >>> Actual [0
> > >>> ]
> > >>> $
> > >> On IRC the other day Roman mentioned the idea of just replacing "lo" with
> > >> "lo*" on all platforms. I checked the dnsmasq documentation and this simple
> > >> wildcarding is supported for the except-interface option, so I tried out
> > >> such a patch on my system and it seems to work properly. Maybe we should do
> > >> that instead of having yet another chunk of #ifdef __linux__ code (the test
> > >> case datafiles will still need to be changed, but at least they'll be
> > >> identical for all platforms).
> > > Any idea how far back wildcards work.  If they still work on the RHEL-6
> > > vintage dnsmasq, then I'd agree with you and it'll make the test case
> > > fix easier to avoid the conditional.
> > 
> > Time for the "Monday Sigh". Sigh.
> > 
> > I looked this up in dnsmasq's git repo, and it seems recognition of 
> > wildcards in interface names was added in
> > 
> >    commit 49333cbdbef3bf86198b31a42bffad002de305d5
> >    Author: Simon Kelley <simon at thekelleys.org.uk>
> >    Date:   Fri Mar 15 20:30:51 2013 +0000
> > 
> >        Allow trailing '*' wildcard in interface names.
> > 
> > That commit was first in dnsmasq 2.66, but RHEL6 is using dnsmasq 2.48.
> > 
> > The strange thing is that I tried running dnsmasq on RHEL6 with 
> > "--except-interface=lo*" and was able to run multiple instances. I guess 
> > my test was flawed. (NetworkManager doesn't support use of dnsmasq for 
> > DNS services, as Cole suggested as a test in:
> > 
> >    https://bugzilla.redhat.com/show_bug.cgi?id=886663#c2
> > 
> > But the source doesn't lie.)
> > 
> > So I guess we need to parameterize the tests somehow (this seems 
> > familiar, but I can't remember why).
> 
> Another option could be to create two except-interface items in the
> configuration, "lo" and "lo0", regardless the OS. It seems like
> dnsmasq supports multiple arguments for --interface and
> --except-interface for a decade (I went back to v2.32 cca 2006, feel
> free to double check). If the lo* solution proposed above was deemed
> safe, just matching two specific interface names instead of everything
> starting with "lo" should be even more safe.
> 
> What do you think? Should I go ahead and send the patch implementing
> my above proposal?

Yeah, I think this approach was discussed on IRC. I think it has
some advantages (it's simple and doesn't need #ifdefs) though it's not
the most elegant thing to list obviously unneeded interfaces.

OTOH, if there are no other feature that could benefit from parametrized
test files, it probably doesn't make much sense to complicate things...

Roman Bogorodskiy
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