Re: [Xen-devel] Re: [PATCH 1/3] xen: pvhvm: allow user to request no emulated device unplug

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2010-08-19 at 11:50 +0100, Ian Campbell wrote:
> On Thu, 2010-08-19 at 11:37 +0100, Stefano Stabellini wrote:
> > On Thu, 19 Aug 2010, Ian Campbell wrote:
> > >   if (r && !(r == XEN_PLATFORM_ERR_MAGIC &&
> > > +                 (xen_emul_unplug != -1) &&
> > >                   (xen_emul_unplug & XEN_UNPLUG_IGNORE)))
> > 
> > I wouldn't add xen_emul_unplug != -1 because it should be clear that
> > xen_emul_unplug & XEN_UNPLUG_IGNORE always implies xen_emul_unplug != -1.
> 
> That's not correct since -1 is all 1s. So you can get a false positive
> for "xen_emul_unplug & XEN_UNPLUG_IGNORE" if xen_emul_unplug == -1.

IOW if we were to rewrite the test to use less boolean logic the patch
might look like:

        if (r) {
                if (r != XEN_PLATFORM_ERR_MAGIC)
                        return;
+               if (xen_emul_unplug == -1)
+                       return;
                if (!(xen_emul_unplug & XEN_UNPLUG_IGNORE))
                        return;
        }

Perhaps this refactoring is worthwhile in any case? It certainly makes
my head hurt less ;-)

Ian.



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