Re: [Xen-devel] [PATCH V4 19/24] xl: introduce and use "xl-json" format

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

> > I suppose the question is would any other toolstack which
> > wanted to save a libxl_domain_config in this way want to use the same
> > userid or a different one?
> > 
> 
> I am not sure if any other toolstack will use the same format. libvirt
> has its own entry called "libvirt-xml". 

Does it seem implausible that some hypothetical toolstack would also
want to save the pickled content of libxl_domain_config?

(I'm not sure what libvirt uses libvirt-xml for, it seems mostly to be
just to detect if this is a libvirt managed domain).

> > By using a common one could we perhaps fix the issue of not being able
> > to poke at e.g. libvirt domain using xl? (specifically things like xl
> > list -v on a system with a mix of domains does odd things IIRC).
> > 
> 
> Not really, at least not without making libvirt use the same stored
> data, or not without xl being able to consume libvirt-xml.

What I meant to suggest was that if libxl took care of saving a
libxl_domain_config for each domain then it could work for any toolstack
which cared to opt into using it.

> > Perhaps storing (and all the updating) this thing is something which
> > libxl rather than xl should take care of? With a function
> > libxl_domain_fetch_config(ctx, domid, &libxl_domain_config)? 
> > 
> 
> As I stated in 00 I wasn't sure about this either. It's a design
> decision which needs more input.
> 
> One thing that makes me feel weird is that having libxl to manage domain
> state -- that means a library is managing domain state? My gut feeling
> is that it should be a "tool" not a "library" that manages domain
> states.

libxl manages the "state" in xenstore too I suppose, and libxl is
responsible for modifying the state so it isn't that weird to consider
that it might also be able to answer the question "what is the current
state". You've implemented that by saving the domain config as JSON, I
had previously thought that libxl could reconstitute the domain config
from the other state (I think your way is better, but in some sense this
could be considered an internal implementation detail of a libxl
interface).

Ian.



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