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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 19 Aug 2010, Ian Campbell wrote:
> 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 ;-)
> 
 
Yeah, it is probably worth it anyway :)


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