On Mon, 19 Jun 2023 14:49:42 +1000
David Gibson <david(a)gibson.dropbear.id.au> wrote:

...
  On Fri, Jun 16, 2023 at 11:04:00PM +0200, Stefano
Brivio wrote:
  On Thu, 15 Jun 2023 14:57:37 +0200
 Paul Holzinger <pholzing(a)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. 
 
 So, I'm actually a bit hesitant about applying this treatment (allow
 multiple, last one wins) to -a specifically.  The reason being that we
 have draft plans to allow multiple addresses within the guest/ns.
 That might logically lead to allowing arbitrary numbers of -a options
 in future, where *all* the addresses apply.  If we'd previously
 allowed multiple options, but only the last one applies, that might be
 a breaking semantic change. 
Uh oh, right... and it might also apply to -g / --gateway eventually.

On the other hand: are two semantic changes (both of which not breaking
any reasonable or expected previous usage) in a relatively short period
of time so much worse than one (we plan to change -a handling anyway)?

I guess handling -a differently in Podman's options would still be
additional effort for Paul. In my opinion, as long as we keep man pages
updated, we should still prioritise making our lives (and the code!)
easier.

-- 
Stefano

On Tue, 20 Jun 2023 16:50:49 +0200
Paul Holzinger <pholzing(a)redhat.com> wrote:

...
  On 19/06/2023 08:18, Stefano Brivio wrote:
  On Mon, 19 Jun 2023 14:49:42 +1000
 David Gibson <david(a)gibson.dropbear.id.au> wrote:
  
  On Fri, Jun 16, 2023 at 11:04:00PM +0200, Stefano
Brivio wrote:  
  On Thu, 15 Jun 2023 14:57:37 +0200
 Paul Holzinger <pholzing(a)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.   
 So, I'm actually a bit hesitant about applying this treatment
(allow
 multiple, last one wins) to -a specifically.  The reason being that we
 have draft plans to allow multiple addresses within the guest/ns.
 That might logically lead to allowing arbitrary numbers of -a options
 in future, where *all* the addresses apply.  If we'd previously
 allowed multiple options, but only the last one applies, that might be
 a breaking semantic change.   
 Uh oh, right... and it might also apply to -g /
--gateway eventually.

 On the other hand: are two semantic changes (both of which not breaking
 any reasonable or expected previous usage) in a relatively short period
 of time so much worse than one (we plan to change -a handling anyway)?

 I guess handling -a differently in Podman's options would still be
 additional effort for Paul. In my opinion, as long as we keep man pages
 updated, we should still prioritise making our lives (and the code!)
 easier. 
 If you plan to make changes like that I agree that supporting it might 
 result in possible breaking changes for some users. 
Yes, but for how long...? I think we can really prefer a simple
solution (as long as man pages are updated) and accept that we'll
(slightly) change the behaviour twice.

It's not even the expected usage, it's about going through:

1. reporting errors with multiple options (logically invalid)

2. not reporting errors with multiple options (logically invalid, some
   useless)

3. not reporting errors with multiple options (logically valid, all
   useful)

if somebody is in case 2., their configuration (that we'll be "fixing"
all of a sudden) is kind of problematic anyway.

...
  However I like to point out that the current behavior
is inconsistent 
 and only works for some options which is the reason I thought this would 
 work in the first place, namely it works fine with `--ns-mac-addr` right 
 now. 
Right, also that.

...
  Another option for Podman would be to discard the
options from the conf 
 file when cli options are set so it is either or. Easy to do but I think 
 it is not so great for users as this means a user would need to type all 
 options again if they just want to change a single one. 
To me that looks much more confusing than any slight "breakage" we
might have as a result.

Nah, really, let's not overcomplicate this. I think the biggest problem
for users at the moment is that we all struggle to find the time to
implement "nice" things they would be eager to use.

I'd suggest to just go ahead with what you were proposing at the
beginning. I also talked with David on the weekly call yesterday and
he's fine with this.

-- 
Stefano