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

[Gianni Tedesco <gianni.tedesco@citrix.com>]

On Thu, 2010-08-19 at 17:10 +0100, Jeremy Fitzhardinge wrote:
> On 08/19/2010 03:54 AM, Stefano Stabellini wrote:
> > 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 :)
> 
> Treating a variable as an integer and a bitfield seems like a bad idea.

Should be fine? I'd just #define XEN_UNPLUG_ALL_THE_BITS ~0U for the
sake of cosmetics...