netdev - Re: [PATCH net-next] ipv6: do not merge differe type and protocol routes

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Date: Fri, 1 Sep 2023 11:58:54 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Ido Schimmel <idosch@...sch.org>,
	Thomas Haller <thaller@...hat.com>
Subject: Re: [PATCH net-next] ipv6: do not merge differe type and protocol
 routes

On Thu, Aug 31, 2023 at 01:58:48PM +0200, Nicolas Dichtel wrote:
> > The append should also works for a single route, not only for append nexthop, no?
> I don't think so. The 'append' should 'join', not add. Adding more cases where a
> route is added instead of appended doesn't make the API clearer.
> 
> With this patch, it will be possible to add a new route with the 'append'
> command when the 'add' command fails:
> $ ip -6 route add local 2003:1:2:3::/64 via 2001::2 dev eth1 table 200
> $ ip -6 route add unicast 2003:1:2:3::/64 via 2001::2 dev eth1 table 200
> RTNETLINK answers: File exists
> 
> $ ip -6 route add 2003:1:2:3::/64 via 2001::2 dev eth1 protocol bgp table 200
> $ ip -6 route add 2003:1:2:3::/64 via 2001::2 dev eth1 protocol kernel table 200
> RTNETLINK answers: File exists
> 
> This makes the API more confusing and complex. And I don't understand how it
> will be used later. There will be 2 routes on the system, but only one will be
> used, which one? This is confusing.

Just to makeit it clear, the new patch will not add two route with only
different type/protocol. Here is the result with my patch.

+ ip -6 route flush table 300
+ ip link add dummy1 up type dummy
+ ip link add dummy2 up type dummy
+ ip addr add 2001:db8:101::1/64 dev dummy1
+ ip addr add 2001:db8:101::2/64 dev dummy2
+ ip route add local 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 table 100
+ ip route append unicast 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 table 100
RTNETLINK answers: File exists

     ^^ here the append still failed

+ ip route append unicast 2001:db8:103::/64 via 2001:db8:101::10 dev dummy2 table 100
+ ip -6 route show table 100
local 2001:db8:103::/64 via 2001:db8:101::10 dev dummy1 metric 1024 pref medium
2001:db8:103::/64 via 2001:db8:101::10 dev dummy2 metric 1024 pref medium
+ ip route add 2001:db8:104::/64 via 2001:db8:101::10 dev dummy1 proto kernel table 200
+ ip route append 2001:db8:104::/64 via 2001:db8:101::10 dev dummy1 proto bgp table 200
RTNETLINK answers: File exists

     ^^ And here

+ ip route append 2001:db8:104::/64 via 2001:db8:101::10 dev dummy2 proto bgp table 200
+ ip -6 route show table 200
2001:db8:104::/64 via 2001:db8:101::10 dev dummy1 proto kernel metric 1024 pref medium
2001:db8:104::/64 via 2001:db8:101::10 dev dummy2 proto bgp metric 1024 pref medium

Thanks
Hangbin