netdev - Re: [BUG] iproute2 - ip -d -j tuntap outputs malformed JSON

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Message-ID: <20251121161007.4c7ebae6@phoenix.local>
Date: Fri, 21 Nov 2025 16:10:07 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Zhengyi Fu <i@...y.me>
Cc: netdev@...r.kernel.org
Subject: Re: [BUG] iproute2 - ip -d -j tuntap outputs malformed JSON

On Fri, 21 Nov 2025 12:25:41 +0800
Zhengyi Fu <i@...y.me> wrote:

> Hi iproute2 maintainers,
> 
>     $ sudo ip -d -j tuntap
>     [{"ifname":"tun0","flags":["tun","persist"],"processes":["name":"ssh","pid":86812]}]
> 
> The “processes” value looks like it should be an array of objects, so
> the inner braces seem to be missing:
> 
>     [{"ifname":"tun0","flags":["tun","persist"],"processes":[{"name":"ssh","pid":86812}]}]
> 
> Could you confirm whether this is a formatting bug or if the output is
> intentionally flattened?
> 
> Thanks!
> 

It should be an array of objects. You can confirm by seeing the output
with multiple processes.

Does this fix it?

diff --git a/ip/iptuntap.c b/ip/iptuntap.c
index b7018a6f..6718ec6c 100644
--- a/ip/iptuntap.c
+++ b/ip/iptuntap.c
@@ -314,6 +314,7 @@ static void show_processes(const char *name)
                                   !strcmp(name, value)) {
                                SPRINT_BUF(pname);
 
+                               open_json_object(NULL);
                                if (get_task_name(pid, pname, sizeof(pname)))
                                        print_string(PRINT_ANY, "name",
                                                     "%s", "<NULL>");
@@ -322,6 +323,7 @@ static void show_processes(const char *name)
                                                     "%s", pname);
 
                                print_uint(PRINT_ANY, "pid", "(%d)", pid);
+                               close_json_object();
                        }
 
                        free(key);