netdev - Re: [PATCH RESEND v2 net-next 04/14] ipv6: Check GATEWAY in rtm_to_fib6_multipath

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Message-ID: <1c382acc-d823-47e9-902d-42606d64daf1@redhat.com>
Date: Wed, 16 Apr 2025 11:06:30 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>,
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuni1840@...il.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH RESEND v2 net-next 04/14] ipv6: Check GATEWAY in
 rtm_to_fib6_multipath_config().

On 4/14/25 8:14 PM, Kuniyuki Iwashima wrote:
> In ip6_route_multipath_add(), we call rt6_qualify_for_ecmp() for each
> entry.  If it returns false, the request fails.
> 
> rt6_qualify_for_ecmp() returns false if either of the conditions below
> is true:
> 
>   1. f6i->fib6_flags has RTF_ADDRCONF
>   2. f6i->nh is not NULL
>   3. f6i->fib6_nh->fib_nh_gw_family is AF_UNSPEC
> 
> 1 is unnecessary because rtm_to_fib6_config() never sets RTF_ADDRCONF
> to cfg->fc_flags.
> 
> 2. is equivalent with cfg->fc_nh_id.
> 
> 3. can be replaced by checking RTF_GATEWAY in the base and each multipath
> entry because AF_INET6 is set to f6i->fib6_nh->fib_nh_gw_family only when
> cfg.fc_is_fdb is true or RTF_GATEWAY is set, but the former is always
> false.
> 
> Let's perform the equivalent checks in rtm_to_fib6_multipath_config().

It's unclear to me the 'why'???

Thanks,

Paolo