[ovs-dev] [mcgroup 2/4] datapath: Hardcode vport multicast group ID on older kernels.

[Ben Pfaff]

I can't argue with that.  We could add a way to query it, I guess, if
really necessary.

On Thu, Sep 15, 2011 at 05:04:16PM -0700, Jesse Gross wrote:
> I meant moving the group of fallback IDs would break things.
> 
> On Thu, Sep 15, 2011 at 5:01 PM, Ben Pfaff <blp at nicira.com> wrote:
> > It wouldn't break the ABI to move either pool around, because those
> > aren't hardcoded in userspace, only in the kernel. ??A discontinuous
> > range would also work but wouldn't be necessary.
> >
> > On Thu, Sep 15, 2011 at 04:55:56PM -0700, Jesse Gross wrote:
> >> I guess the other thing is if we want to increase our pool of
> >> preallocated multicast groups, we have to either break the ABI or make
> >> the current pool discontinuous.
> >>
> >> On Thu, Sep 15, 2011 at 4:48 PM, Ben Pfaff <blp at nicira.com> wrote:
> >> > Personally I'd suggest 33 for this one and increment for each
> >> > succeeding family. ??No one's ever mentioned a problem with our use of
> >> > genetlink groups. ??Since RHEL5 is probably declining rather than
> >> > increasing in deployment, my guess is that no one ever will.
> >> >
> >> > On Thu, Sep 15, 2011 at 04:44:53PM -0700, Jesse Gross wrote:
> >> >> Not really, I don't have any particular opinion on the actual number.
> >> >> The only thing that I was concerned about is what it would look like
> >> >> if we want to do this with the multicast groups for other families.
> >> >>
> >> >> On Thu, Sep 15, 2011 at 4:40 PM, Ethan Jackson <ethan at nicira.com> wrote:
> >> >> > Based on my offline discussions with Jesse I arrived, rather
> >> >> > arbitrarily, at the number 214. ??I don't know enough about the kernel
> >> >> > to judge what a good number choice would be. ??Jesse seemed to think
> >> >> > larger was better. ??I'll use whatever the two of you think is best.
> >> >> >
> >> >> > Ethan
> >> >> >
> >> >> >
> >> >> > On Thu, Sep 15, 2011 at 16:31, Ben Pfaff <blp at nicira.com> wrote:
> >> >> >> On Thu, Sep 15, 2011 at 04:10:55PM -0700, Ethan Jackson wrote:
> >> >> >>> > Where does the number 214 come from?
> >> >> >>>
> >> >> >>> Experimentally I found that the number had to be fairly small. ??I
> >> >> >>> wanted it to be large enough to be unlikely conflict to values the
> >> >> >>> proper way. ??I also wanted a number which was arbitrary to avoid
> >> >> >>> conflicting with other people who may be improperly hardcoding values
> >> >> >>> like this.
> >> >> >>
> >> >> >> We already use genetlink groups 16 through 31 (see
> >> >> >> datapath/linux/compat/genetlink-openvswitch.c) and group 32 (see
> >> >> >> datapath/linux/compat/genetlink-brcompat.c). ??I don't think it makes
> >> >> >> sense to skip all the way to 214. ??Even in 2.6.37 I only see a total
> >> >> >> of 11 defined genetlink multicast groups, so I doubt that anyone's
> >> >> >> going to backport a bunch of them to RHEL 5.
> >> >> >>
> >> >> >
> >> >
> >