netdev - Re: I find one aspect of the ip link show command confusing and I'd like you to fix it, please

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Message-ID: <20170424085407.2b9df529@xeon-e3>
Date:   Mon, 24 Apr 2017 08:54:07 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Jeff Silverman <jeffsilverm@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: I find one aspect of the ip link show command confusing and I'd
 like you to fix it, please

On Sun, 23 Apr 2017 15:36:32 -0700
Jeff Silverman <jeffsilverm@...il.com> wrote:

> People,
> 
> When my NIC is up, but not connected, I see:
> 
> root@...f-desktop:~# ip link show enp3s0
> 2: enp3s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state
> DOWN mode DEFAULT group default qlen 1000
>     link/ether 00:10:18:cc:9c:77 brd ff:ff:ff:ff:ff:ff
> root@...f-desktop:~# ip link show enp3s0
> 
> NO-CARRIER makes sense to me - if the wire is unplugged, then the NIC
> isn't seeing the humm at the beginning of each packet.  That's clear.
> Note that even though my link isn't plugged in,  ip still notes that
> it is up.  That's great.
> 
> 
> But if I down my NIC, there is no indication that it is DOWN other
> than you can't see the UP flag.  If somebody was new to linux, they
> would not see what's not there.
> 
> 2: enp3s0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN mode
> DEFAULT group default qlen 1000
>     link/ether 00:10:18:cc:9c:77 brd ff:ff:ff:ff:ff:ff
> 
> 
> What I would like you to do is modify the ip command so that if the
> NIC has been downed by something, then it explicitly says DOWN.
> 
> What would be really nice would be if you enumerated all of the flags
> that an interface can have, and note if the flag is set or cleared.
> But that's more than what I want with this message.
> 
> 
> Many thanks,
> 
> 
> Jeff
> 

If you have a suggestion send a patch. The utility has shown the same
output since the earliest versions. Therefore the default output format
can't change since people do things like write scripts to parse it.
A more verbose output is possible but would have to be enabled by
a flag.