Re: Option parsing: Allow the same option multiple times

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 15 Jun 2023 14:57:37 +0200
Paul Holzinger <pholzing@redhat.com> wrote:

> Hi all,
> 
> following up on a quick discussion with Stefano on IRC.
> 
> passt/pasta currently rejects most (not all) options when specified 
> multiple times, i.e. pasta -I eth0 -I eth1 ... fails. I think it makes 
> more sense to just use the last one instead.
> 
> My use case: In podman I added a new containers.conf option[1] which 
> allows users to set default pasta cli options. However users can also 
> add options on the podman cli with podman run --net=pasta:... For me it 
> would make the most sense to just append those to the config options and 
> then let pasta deal with it. This allows some form of overwrite 
> mechanism, i.e. by default I may have "-I" , "eth0" in containers.conf 
> but for one specific container I want to use a different interface name 
> and set --net=pasta:-I,eth1 on the cli. Then podman should just hand "-I 
> eth0 -I eth1" to pasta and then pasta picks the last one.
> 
> If we keep the current behavior it means I am forced to parse the 
> options in podman and dedup them which is hard to maintain as podman 
> would need to keep up with pasta upstream.

I had to do something similar in libpod/networking_pasta_linux.go,
which, if you change this, could also be simplified a bit.

> I am willing to send a patch to change this so please let me know if 
> anyone would object to that.

For the record, as I mentioned on IRC, I think it makes sense.

Maybe it's less "correct" as a behaviour, and it would make it a bit
harder for users to spot (unlikely) mistakes on the command line, but
making integrations simpler probably outweighs this.

I don't have a good idea for sentences like "This option can be
specified zero (for defaults) to two times (once for IPv4, once for IPv6)."
that are currently in the man page... maybe we could switch from
"This option can be specified" to "This option specifies one to two..."
and similar.

-- 
Stefano