From: Phil Sutter <phil@nwl.cc>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Thomas Haller <thaller@redhat.com>, netdev@vger.kernel.org
Subject: Re: [PATCH iproute2] ip-address: properly display zero IPv4 peer address
Date: Tue, 24 Nov 2015 12:44:17 +0100 [thread overview]
Message-ID: <20151124114417.GA23115@orbit.nwl.cc> (raw)
In-Reply-To: <20151123160450.73eec3ef@xeon-e3>
On Mon, Nov 23, 2015 at 04:04:50PM -0800, Stephen Hemminger wrote:
> On Thu, 22 Oct 2015 10:34:28 +0200
> Thomas Haller <thaller@redhat.com> wrote:
>
> > Kernel allows for zero IPv4 peer addresses (IFA_ADDRESS):
> >
> > ip address add 192.168.5.1 peer 0.0.0.0/24 dev dummy
> >
> > which is distinct from a usual address like:
> >
> > ip address add 192.168.5.1/24 dev dummy
> > ip address add 192.168.5.1 peer 192.168.5.1/24 dev dummy
> >
> > For IPv4, a missing IFA_ADDRESS attribute means that the peer
> > is 0.0.0.0. See inet_fill_ifaddr(), which does:
> >
> > if ((ifa->ifa_address &&
> > nla_put_in_addr(skb, IFA_ADDRESS, ifa->ifa_address)) ||
> >
> > Signed-off-by: Thomas Haller <thaller@redhat.com>
>
> I would prefer that this apply to both IPv4 and IPv6.
The case that patch handles does not happen in IPv6.
> If the kernel sends back an address, then display it.
It's rather "if the kernel *does not* send back an address ...".
When reviewing this patch, I tried to find an easier (and less ugly)
solution, but failed. Here's the result from testing all variants:
1) ip a a 192.168.1.1/24 dev test0
2) ip a a 192.168.2.1 peer 192.168.2.1/24 dev test0
3) ip a a 192.168.3.1 peer 0.0.0.0/24 dev test0
4) ip a a 192.168.4.1 peer 192.168.4.2 dev test0
5) ip a a feed:babe::1:1/112 dev test0
6) ip a a feed:babe::2:1 peer feed:babe::2:1/112 dev test0
7) ip a a feed:babe::3:1 peer ::/112 dev test0
8) ip a a feed:babe::4:1 peer feed:babe::4:2 dev test0
cmd ifa_local ifa_address
---------------------------------
1) 192.168.1.1 192.168.1.1
2) 192.168.2.1 192.168.2.1
3) 192.168.3.1 unset
4) 192.168.4.1 192.168.4.2
5) unset feed:babe::1:1
6) unset feed:babe::2:1
7) unset feed:babe::3:1
8) feed:babe::4:1 feed:babe::4:2
No idea how this looks for decnet and ipx. Looking only at IPv6 though,
the patch's check for !AF_INET before setting rta_tb[IFA_ADDRESS] =
rta_tb[IFA_LOCAL] could indeed be skipped.
On a side note, I'm pretty sure the later memcmp() could be skipped in
many cases, at least by comparing the pointer values of
rta_tb[IFA_ADDRESS] and rta_tb[IFA_LOCAL].
Cheers, Phil
next prev parent reply other threads:[~2015-11-24 11:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-22 8:34 [PATCH iproute2] ip-address: properly display zero IPv4 peer address Thomas Haller
2015-11-11 11:34 ` Phil Sutter
2015-11-24 0:04 ` Stephen Hemminger
2015-11-24 11:44 ` Phil Sutter [this message]
2015-11-24 12:14 ` Thomas Haller
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