This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-tools] [PATCH] Xenstore mkdir/write implicitly create directori

On Mon, Aug 29, 2005 at 10:12:01AM +1000, Rusty Russell wrote:
> On Fri, 2005-08-26 at 11:28 +0100, Christian Limpach wrote:
> > On Fri, Aug 26, 2005 at 10:20:44AM +1000, Rusty Russell wrote:
> > > Well, we currently don't spuriously fail transactions, because we use
> > > locking to prevent overlapping transactions.  As I've argued repeatedly,
> > > this makes for a nicer programming model.
> > 
> > How do you handle transaction timeouts then?  After all, a guest can
> > get suspended for an arbitrary amount of time and at some point
> > xenstored will have to timeout the transaction and then what?
> This is why suspend takes the xenbus_lock; it just doesn't make sense
> otherwise (even without transactions, you could have issued half a
> command, then get migrated to another machine and another store, and
> you'd be screwed).

I didn't mean checkpointing suspend, but the guest getting descheduled
for an arbitrary amount of time, in the worst case the guest getting
user paused for a very long time.  Bad luck if it's during a transaction
and the store times out the transaction, what then?

> For xenbus, we can do it either way.  But for the tools, we really need
> xenstored to do it, because we need the data to appear in the socket.
> So I think I'll mod xenstored to do it, even though it's a little extra
> traffic (in theory, xenstored could optimize this away if the node has
> *never* existed, but doesn't seem worth it).

Sounds good, thanks!

> > > Domain introductions are the other persistence issue, but they are also
> > > fairly simple.  Indeed, they should be placed in the store...
> > 
> > Sounds good.  I think we also need xenstored to watch for the domain
> > exception virq and remove domains which are dying...
> OK, I wasn't sure if xenstored should do this, or have the tools do it.
> I'll look at the xenstored mods...



Xen-tools mailing list