[Xen-devel] configuring vif options to be consumed by hotplug scripts (Was: Re: [PATCH 4/5] hotplug/linux: Add IPv6 support to the iptables logic)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

Pulling this out into a new subthread. CCing Ian as the other tools
maintainer.

On Tue, 2014-05-20 at 13:58 +0200, Sylvain Munaut wrote:
> >> By default, domains aren't allows to send Router Advertisement
> >> or DHCP responses, see the ipv6_allow_ra to enable them.
> >
> > How does one go about setting this?
> 
> Well ... I thought it would work just like  accel=  (which I'm using
> in prod but that's with 'xm' on 4.1).
> Turns out after a bit of googling that 'accel' might work just by luck
> because somehow at some point passing that option was added to 'xm' in
> 2007 ...
> 
> I just retried now with 'xl' under 4.4 and indeed that doesn't work :(
> 
> So if I want to pass custom parameters to the vif-script, I have to
> add it to libxl ?
> And if yes, is that acceptable ? What would be the best way : add each
> parameter independently, or add a single 'hotplug_extra' parameter
> that would need to be parsed in the hotplug scripts themselves ?

TBH I'm not sure.

Adding the individual options is probably The Right Way(tm), since it
provides a meaningful API for libxl and allows for error checking and
configuring defaults etc. In general adding the ability to pass down an
arbitrary string etc does not lead to a good API.

But, as you've seen, it does have the shortcoming that it does make it
somewhat harder to deploy new configuration items or to do deployment
specific special stuff by adding custom code to vif scripts etc. Often
in cases like this we like to provide the proper way (individual
options) as well as some sort of escape hatch to allow workarounds/local
cfg etc.

Perhaps the existing ability to specify script=my-local-foo is already a
sufficient hatch though? On the the hand if you have some local
configuration option which takes e.g. an integer creating
my-local-foo-1, my-local-foo-2 etc is pretty tedious. Perhaps we could
arrange for it to be possible to pass parameters to the script somehow?

Ian, what do you think? 

Cheers,
Ian.


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