netdev - Re: [PATCH iproute2-next] ip: don't use program name to select command

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Date:   Wed, 13 Jan 2021 20:20:28 -0700
From:   David Ahern <dsahern@...il.com>
To:     Matteo Croce <mcroce@...ux.microsoft.com>, netdev@...r.kernel.org
Cc:     Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH iproute2-next] ip: don't use program name to select
 command

On 1/11/21 12:05 PM, Matteo Croce wrote:
> From: Matteo Croce <mcroce@...rosoft.com>
> 
> ip has an ancient behaviour of looking at its program name to determine
> the command to run. If the name is longer than 2 characters, the first two
> letters are stripped and the others are interpreted as the command name:
> 
>     $ ln -s /sbin/ip iproute
>     $ ln -s /sbin/ip ipa
>     $ ./iproute
>     default via 192.168.55.1 dev wlp0s20f3 proto dhcp metric 600
>     192.168.55.0/24 dev wlp0s20f3 proto kernel scope link src 192.168.55.26 metric 600
>     192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown
>     $ ./ipa show dev lo
>     1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
>         link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>         inet 127.0.0.1/8 scope host lo
>            valid_lft forever preferred_lft forever
> 
> This creates problems when the ip binary is renamed. For example, Yocto
> renames it to 'ip.iproute2' when also the busybox implementation is
> present, giving the following error:
> 
>     $ ip.iproute2
>     Object ".iproute2" is unknown, try "ip help".
> 
> Since noone is using it, remove this undocumented feature.
> 
> Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
> ---
>  ip/ip.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/ip/ip.c b/ip/ip.c
> index 40d2998a..9b772307 100644
> --- a/ip/ip.c
> +++ b/ip/ip.c
> @@ -311,9 +311,6 @@ int main(int argc, char **argv)
>  
>  	rtnl_set_strict_dump(&rth);
>  
> -	if (strlen(basename) > 2)
> -		return do_cmd(basename+2, argc, argv);
> -
>  	if (argc > 1)
>  		return do_cmd(argv[1], argc-1, argv+1);
>  
> 

This has been around for too long to just remove it. How about adding an
option to do_cmd that this appears to be guess based on basename? If the
guess is wrong, fallback to the next do_cmd.