netdev - Re: [PATCH iproute2-next] ip tunnel: add json output

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Date:   Fri, 2 Aug 2019 08:49:33 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Andrea Claudi <aclaudi@...hat.com>
Cc:     linux-netdev <netdev@...r.kernel.org>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH iproute2-next] ip tunnel: add json output

On Fri, 2 Aug 2019 13:14:15 +0200
Andrea Claudi <aclaudi@...hat.com> wrote:

> On Thu, Aug 1, 2019 at 5:16 PM Stephen Hemminger
> <stephen@...workplumber.org> wrote:
> >
> > On Thu,  1 Aug 2019 12:12:58 +0200
> > Andrea Claudi <aclaudi@...hat.com> wrote:
> >  
> > > Add json support on iptunnel and ip6tunnel.
> > > The plain text output format should remain the same.
> > >
> > > Signed-off-by: Andrea Claudi <aclaudi@...hat.com>
> > > ---
> > >  ip/ip6tunnel.c | 82 +++++++++++++++++++++++++++++++--------------
> > >  ip/iptunnel.c  | 90 +++++++++++++++++++++++++++++++++-----------------
> > >  ip/tunnel.c    | 42 +++++++++++++++++------
> > >  3 files changed, 148 insertions(+), 66 deletions(-)
> > >
> > > diff --git a/ip/ip6tunnel.c b/ip/ip6tunnel.c
> > > index d7684a673fdc4..f2b9710c1320f 100644
> > > --- a/ip/ip6tunnel.c
> > > +++ b/ip/ip6tunnel.c
> > > @@ -71,57 +71,90 @@ static void usage(void)
> > >  static void print_tunnel(const void *t)
> > >  {
> > >       const struct ip6_tnl_parm2 *p = t;
> > > -     char s1[1024];
> > > -     char s2[1024];
> > > +     SPRINT_BUF(b1);
> > >
> > >       /* Do not use format_host() for local addr,
> > >        * symbolic name will not be useful.
> > >        */
> > > -     printf("%s: %s/ipv6 remote %s local %s",
> > > -            p->name,
> > > -            tnl_strproto(p->proto),
> > > -            format_host_r(AF_INET6, 16, &p->raddr, s1, sizeof(s1)),
> > > -            rt_addr_n2a_r(AF_INET6, 16, &p->laddr, s2, sizeof(s2)));
> > > +     open_json_object(NULL);
> > > +     print_string(PRINT_ANY, "ifname", "%s: ", p->name);  
> >
> > Print this using color for interface name?  
> 
> Thanks for the suggestion, I can do the same also for remote and local
> addresses?
> 
> >
> >  
> > > +     snprintf(b1, sizeof(b1), "%s/ipv6", tnl_strproto(p->proto));
> > > +     print_string(PRINT_ANY, "mode", "%s ", b1);
> > > +     print_string(PRINT_ANY,
> > > +                  "remote",
> > > +                  "remote %s ",
> > > +                  format_host_r(AF_INET6, 16, &p->raddr, b1, sizeof(b1)));
> > > +     print_string(PRINT_ANY,
> > > +                  "local",
> > > +                  "local %s",
> > > +                  rt_addr_n2a_r(AF_INET6, 16, &p->laddr, b1, sizeof(b1)));
> > > +
> > >       if (p->link) {
> > >               const char *n = ll_index_to_name(p->link);
> > >
> > >               if (n)
> > > -                     printf(" dev %s", n);
> > > +                     print_string(PRINT_ANY, "link", " dev %s", n);
> > >       }
> > >
> > >       if (p->flags & IP6_TNL_F_IGN_ENCAP_LIMIT)
> > > -             printf(" encaplimit none");
> > > +             print_bool(PRINT_ANY,
> > > +                        "ip6_tnl_f_ign_encap_limit",
> > > +                        " encaplimit none",
> > > +                        true);  
> >
> > For flags like this, print_null is more typical JSON than a boolean
> > value. Null is better for presence flag. Bool is better if both true and
> > false are printed.  
> 
> Using print_null json JSON output becomes:
> 
>   {
>     "ifname": "gre2",
>     "mode": "gre/ipv6",
>     "remote": "fd::1",
>     "local": "::",
>     "ip6_tnl_f_ign_encap_limit": null,
>     "hoplimit": 64,
>     "tclass": "0x00",
>     "flowlabel": "0x00000",
>     "flowinfo": "0x00000000",
>     "flags": []
>   }
> 
> Which seems a bit confusing to me (what does the "null" value means?).
> Using print_null we also introduce an inconsistency with the JSON
> output of ip/link_gre6.c and ip/link_ip6tnl.c.
> I would prefer to use print_bool and print out
> ip6_tnl_f_ign_encap_limit both when true and false, patching both
> files above to do the same. WDYT?

JSON has several ways to represent the same type of flag value.
Since JSON always has key/value. Null is used to indicate something is present and
in that case the value is unnecessary, which is what the null field was meant for.