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

[Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>]

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...

Great!

    christian


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