From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Subject: Re: [PATCH net-next] ipv6: export IP6_RT_PRIO_* to userland
Date: Mon, 05 Nov 2012 20:24:42 +0100
Message-ID: <5098127A.2040405@6wind.com>
References: <1352129298-1104-1-git-send-email-nicolas.dichtel@6wind.com> <20121105.120017.1189906314924845791.davem@davemloft.net> <5097F5DF.7040507@6wind.com> <20121105.124305.1002288640313724910.davem@davemloft.net>
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To: David Miller <davem@davemloft.net>
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Le 05/11/2012 18:43, David Miller a =E9crit :
> From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> Date: Mon, 05 Nov 2012 18:22:39 +0100
>
>> Le 05/11/2012 18:00, David Miller a =E9crit :
>>> From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
>>> Date: Mon,  5 Nov 2012 16:28:18 +0100
>>>
>>>> The kernel uses some default metric when routes are managed. For
>>>> example, a
>>>> static route added with a metric set to 0 is inserted in the kerne=
l
>>>> with
>>>> metric 1024 (IP6_RT_PRIO_USER).
>>>> It is useful for routing daemons to know these values, to be able =
to
>>>> set routes
>>>> without interfering with what the kernel does.
>>>>
>>>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
>>>
>>> But these belong in the libc headers anyways.
>>>
>>> If we haven't provided them for so long, there's no real value of
>>> adding them now.
>>>
>> But how can a daemon know which default values are used? If it wants
>> to add a route with metric =3D default + x, it should first add it w=
ith
>> metric =3D 0, check the result and then change the metric.
>
> What do we do on the ipv4 side and how do daemons cope in that situat=
ion?
>
In IPv4, there is no such default metric. If you add a route with metri=
c X, it=20
remains X in the kernel, even if it's 0.