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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, May 07, 2014 at 12:30:30PM +0100, Ian Campbell wrote:
> > > 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.
> 

OK, it makes sense.

> > > 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).
> 

OK. Then I shall push the configuration synchronization down to libxl
level.

Wei.

> Ian.
> 

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