netdev - Re: Is the manpage wrong for "ip address delete"?

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Message-ID: <20240713223112.4d5db4b6@hermes.local>
Date: Sat, 13 Jul 2024 22:31:12 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Donald Hunter <donald.hunter@...il.com>
Cc: Adam Nielsen <a.nielsen@...kadi.net>, netdev@...r.kernel.org
Subject: Re: Is the manpage wrong for "ip address delete"?

On Fri, 12 Jul 2024 11:33:45 +0100
Donald Hunter <donald.hunter@...il.com> wrote:

> Adam Nielsen <a.nielsen@...kadi.net> writes:
> 
> > Hi all,
> >
> > I'm trying to remove an IP address from an interface, without having to
> > specify it, but the behaviour doesn't seem to match the manpage.
> >
> > In the manpage for ip-address it states:
> >
> >     ip address delete - delete protocol address
> >        Arguments: coincide with the arguments of ip addr add.  The
> >        device name is a required  argument. The rest are optional.  If no
> >        arguments are given, the first address is deleted.
> >
> > I can't work out how to trigger the "if no arguments are given" part:
> >
> >   $ ip address delete dev eth0
> >   RTNETLINK answers: Operation not supported
> >
> >   $ ip address delete "" dev eth0
> >   Error: any valid prefix is expected rather than "".
> >
> >   $ ip address dev eth0 delete
> >   Command "dev" is unknown, try "ip address help".
> >
> > In the end I worked out that "ip address flush dev eth0" did what I
> > wanted, but I'm just wondering whether the manpage needs to be updated
> > to reflect the current behaviour?  
> 
> Yes, that paragraph of the manpage appears to be wrong. It does not
> match the manpage synopsis, nor the usage from "ip address help" which
> both say:
> 
>   ip address del IFADDR dev IFNAME [ mngtmpaddr ]
> 
> The description does match the kernel behaviour for a given address
> family, which you can see by using ynl:
> 
> $ ip a show dev veth0
> 2: veth0@...h1: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN group default qlen 1000
>     link/ether 6a:66:c7:67:bc:81 brd ff:ff:ff:ff:ff:ff
>     inet 6.6.6.6/24 scope global fred
>        valid_lft forever preferred_lft forever
>     inet 2.2.2.2/24 scope global veth0
>        valid_lft forever preferred_lft forever
>     inet 4.4.4.4/24 scope global veth0
>        valid_lft forever preferred_lft forever
> 
> $ sudo ./tools/net/ynl/cli.py \
>   --spec Documentation/netlink/specs/rt_addr.yaml \
>   --do deladdr --json '{"ifa-family": 2, "ifa-index": 2}'
> None
> 
> $ ip a show dev veth0
> 2: veth0@...h1: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN group default qlen 1000
>     link/ether 6a:66:c7:67:bc:81 brd ff:ff:ff:ff:ff:ff
>     inet 2.2.2.2/24 scope global veth0
>        valid_lft forever preferred_lft forever
>     inet 4.4.4.4/24 scope global veth0
>        valid_lft forever preferred_lft forever
> 
> I guess it makes sense for "ip address del" to be stricter since 'first
> address' is quite arbitrary behaviour.

I wonder if it used to work long ago in some early version (like 2.4) and
got broken and no one ever noticed