netdev - Re: [PATCH iproute2] vxlan: show correct ttl inherit info

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Message-ID: <20180927092745.GV14666@orbyte.nwl.cc>
Date:   Thu, 27 Sep 2018 11:27:45 +0200
From:   Phil Sutter <phil@....cc>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     netdev@...r.kernel.org,
        Stephen Hemminger <stephen@...workplumber.org>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH iproute2] vxlan: show correct ttl inherit info

Hi Hangbin,

On Thu, Sep 27, 2018 at 03:28:36PM +0800, Hangbin Liu wrote:
> We should only show ttl inherit when IFLA_VXLAN_TTL_INHERIT supplied.
> Otherwise show the ttl number, or auto when it is 0.
> 
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  ip/iplink_vxlan.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/ip/iplink_vxlan.c b/ip/iplink_vxlan.c
> index 831f39a..7fc0e2b 100644
> --- a/ip/iplink_vxlan.c
> +++ b/ip/iplink_vxlan.c
> @@ -145,7 +145,7 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
>  			NEXT_ARG();
>  			check_duparg(&attrs, IFLA_VXLAN_TTL, "ttl", *argv);
>  			if (strcmp(*argv, "inherit") == 0) {
> -				addattr_l(n, 1024, IFLA_VXLAN_TTL_INHERIT, NULL, 0);
> +				addattr(n, 1024, IFLA_VXLAN_TTL_INHERIT);

So for VXLAN, the attribute is just added but with a zero value. Looking
at respective kernel code, this seems fine. Now I wonder why for Geneve,
you set the value to 1 and when displaying explicitly check whether the
attribute is there *and* non-zero. OK, looks like Geneve driver always
exports IFLA_GENEVE_TTL_INHERIT. Oddly, I can't find where VXLAN driver
in kernel does export the IFLA_VXLAN_TTL_INHERIT attribute. Am I missing
something?
Do you know why handling of the attributes in both drivers differ?

Cheers, Phil