Re: [Xen-devel] [PATCH] disable virtfs compilation by default in upstream QEMU

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-06-12 at 11:30 +0100, Stefano Stabellini wrote:
> On Mon, 11 Jun 2012, Ian Jackson wrote:
> > Stefano Stabellini writes ("Re: [Xen-devel] [PATCH] disable virtfs 
> > compilation by default in upstream QEMU"):
> > > On Fri, 8 Jun 2012, Ian Jackson wrote:
> > > > So what is the default configuration ?
> > > 
> > > The default is on.
[...]
> virtfs is not enabled unless you pass specific arguments to QEMU,
> which we do not.

OK, so it doesn't really default to on as you said above. Rather the
feature is compiled in but disabled by default. This is much safer.

> Besides saying that an open source technology X is dangerous because it
> has been developed by a different community than ours, without giving
> any technical reasons for it, is just spreading FUD.
[...]

I do think we need to consider the impact of (perhaps unintentionally)
enabling things which may cause interactions which the relevant upstream
and/or we may not have anticipated. 

We especially need to consider this in the case where a new thing is
enabled by default -- which is no longer believed to be the case with
virtfs but imagine for example if virtfs were on by default then the
admin might need to take steps to lock down the directory which it
exported to the guest by default or something. That might come as a
surprise if the admin didn't actually ask for virtfs and has know idea
that it even exists.

Since virtfs is actually off by default I don't think we have much to
worry about.

> > And this is relevant because we're now using upstream qemu 1.0 by
> > default for some guests.
> 
> Only in PV guests, for which this discussion is not relevant.

Ian.


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