netdev - Re: [PATCH v3 1/3] iproute2: add support for setting device groups

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Date:	Wed, 2 Feb 2011 11:13:15 +0200
From:	Vlad Dogaru <ddvlad@...edu.org>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	netdev@...r.kernel.org, Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH v3 1/3] iproute2: add support for setting device groups

On Wed, Feb 02, 2011 at 09:56:28AM +0100, Patrick McHardy wrote:
> On 26.01.2011 17:41, Vlad Dogaru wrote:
> > Use the group keyword to specify what group the device should belong to.
> > Since the kernel uses numbers internally, mapping of group names to
> > numbers is defined in /etc/iproute2/group_map. Example usage:
> > 
> >   ip link set dev eth0 group default
> > 
> > @@ -297,6 +299,13 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
> >  			if (get_integer(&mtu, *argv, 0))
> >  				invarg("Invalid \"mtu\" value\n", *argv);
> >  			addattr_l(&req->n, sizeof(*req), IFLA_MTU, &mtu, 4);
> > +		} else if (strcmp(*argv, "group") == 0) {
> > +			NEXT_ARG();
> > +			if (group != -1)
> > +				duparg("group", *argv);
> > +			if (lookup_map_id(*argv, &group, GROUP_MAP))
> > +				invarg("Invalid \"group\" value\n", *argv);
> > +			addattr_l(&req->n, sizeof(*req), IFLA_GROUP, &group, 4);
> 
> I think it would be preferrable to use a function similar to
> rt_realm_n2a() that can also handle plain numerical values.

The a2n() functions are rather complex for this case: they employ
caching and store a table. I suppose this is because multiple calls to
them are possible in a single run and the correspondence has to be made
in both ways (a2n and n2a).

A network group is only converted to a number at most once for each ip
process spawned, so storing a table is not really helpful. What could,
however, help is using get_integer before lookup_map_id. Only if
get_integer fails would we lookup the symbolic group name.

Does that make sense?
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