Re: [Xen-devel] [PATCH] xl: Check for dependencies in xl

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

On Mon, 2011-01-24 at 17:26 +0000, Kamala Narasimhan wrote:
> > 
> > NAK
> > 
> > Actually I think this type of check should go after the xenstore open
> > has failed, just as an informational/hint type of thing IF it fails.
> > Rather than applying what is really a heuristic and making it CAUSE a
> > failure.
> > 
> Except xs_daemon_open called within libxl_ctx_init does not fail when
> xenstored is not running!  We get this non-obvious error message -
> "failed to free memory for the domain" at a later point.  This patch
> was an attempt to make the "xenstored not running" issue more
> obvious.  

Oh yes, I didn't pick up on that.

> So, without this check we might have to end up chasing xs_* calls that
> are bound to fail because of using the non null xs_handle returned by
> xs_daemon_open and apply this heuristic upon its failure to make the
> issue more obvious.  Given this info, do you still think we shouldn't
> perform this check?  It would certainly make troubleshooting easier.

I think the idea of having such heuristic checks is a good one. Error
messages can be a bit baffling.

> Alternately, we could investigate why xs_daemon_open is returning a
> non null handle when xenstored is not running.

Sounds like a good idea since, if that is the case, how can a caller
know whether it really got a xenstore connection or not? Maybe we can
just try and ls / and that will fail?

I would like to hear Ian Campbells opinion on this but he's away until
Wednesday I think.

Gianni


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