Re: [Xen-devel] [PATCH v1 03/10] libxl: store a copy of vanilla domain configuration when creating domain

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jul 25, 2014 at 04:01:06PM +0100, Ian Jackson wrote:
[...]
> > > > +    /* update network interface information */
> ...
> > > Does creating the config early, and then updating it, not mean that
> > > there will be a window during domain creation when configuration
> > > exists but lacks these updates ?
> > > 
> > > I think that might be a (theoretically application-visible) bug.
> > 
> > Yes, there's such windows.
> > 
> > Ian C suggested I add lock during creation, which I think should fix
> > this problem.
> 
> I don't think that's a particularly good idea.  Such a lock would
> presumably cover most of the domain creation work (hotplug scripts
> etc) which might take a long time.
> 
> During that time various operations would block unreasonably.
> 

That's a bit unfortunate. But what can we do to close that window?
I think no good will come out if I try to fiddle with domain state
during creation anyway, so locking like this may be acceptable?

> Also, I think you mustn't use an fcntl lock across ao operation
> callback chains.  fcntl locks do not exclude other threads in the same
> process.
> 

Then we need both mutex and file lock? Mutex to protect against threads
in the same process while file lock protect against other processes.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel