Re: [Xen-devel] [PATCH 5 of 9] libxl: add libxl_domain_preserve

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Mon, 2010-07-26 at 16:30 +0100, Ian Jackson wrote:
> Ian Campbell writes ("[Xen-devel] [PATCH 5 of 9] libxl: add 
> libxl_domain_preserve"):
> > This method is intended to preserve an existing domain (for debugging
> > purposes) in such a way that the domain can also be restarted.
> 
> This sounds interesting, but I'm not quite sure what the semantics are
> intended to be.  I guess it works on an existing running domain or a
> paused one.  Does it stop the domain's execution ?

It was intended to be used to implement the rename-restart action for
the on_reboot (and on_crash I guess) actions which I introduce in a
later patch.

I only added this option because xend has it -- I'd be just as happy to
only implement simple restart until someone who wants the behaviour
comes along. In the meantime preserve or coredump-restart are pretty
good substitutes for rename-restart. 

Anyhow the actual actual semantics of libxl_domain_preserve is that it
acts on a shutdown (but not destroyed) domain. The name and/or comments
could certainly better reflect this.

> The current code seems mainly to change the name and the uuid in
> xenstore - to a specified new uuid - which seems a strange thing to
> do.

It's (a subset of) what xend does ;-) (For reference its
XendDomainInfo._preserveForRestart from
tools/python/xen/xend/XendDomainInfo.py)

I suspect the reason is something to do with not nuking /vm/<uuid> for a
running domain when destroying a previously preserved instance of that
domain.

Ian.



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