Re: [Xen-devel] [PATCH v4 4/6] x86/PV: allow PV guests to have an emulated PIT

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2016-01-22 at 03:48 -0700, Jan Beulich wrote:
> > > > On 21.01.16 at 17:51, <roger.pau@xxxxxxxxxx> wrote:
> > This fixes the fallout from the HVMlite series, that removed the
> > emulated
> > PIT from PV(H) guests. Also, this patch forces the hardware domain to
> > always have an emulated PIT, regardless of whether the toolstack
> > specified
> > one or not.
> > 
> > Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> albeit ...
> 
> > --- a/xen/arch/x86/domain.c
> > +++ b/xen/arch/x86/domain.c
> > @@ -542,8 +542,11 @@ int arch_domain_create(struct domain *d, unsigned
> > int 
> > domcr_flags,
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂd->domain_id, config->emulation_flags);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂreturn -EINVAL;
> > ÂÂÂÂÂÂÂÂÂ}
> > +ÂÂÂÂÂÂÂÂif ( is_hardware_domain(d) )
> > +ÂÂÂÂÂÂÂÂÂÂÂÂconfig->emulation_flags |= XEN_X86_EMU_PIT;
> > ÂÂÂÂÂÂÂÂÂif ( config->emulation_flags != 0 &&
> > -ÂÂÂÂÂÂÂÂÂÂÂÂÂ(!is_hvm_domain(d) || config->emulation_flags !=
> > XEN_X86_EMU_ALL) )
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂ(is_hvm_domain(d) ? (config->emulation_flags !=
> > XEN_X86_EMU_ALL) :
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ(config->emulation_flags !=
> > XEN_X86_EMU_PIT)) )
> > ÂÂÂÂÂÂÂÂÂ{
> 
> ... you having chosen the != route instead of the suggested &
> one, I guess I'll take the liberty to further simplify this while
> committing (as the ?: is now only needed on the right side of the
> != and I'm generally of the opinion that redundancy like this is
> hampering readability).

Readability would be even greater IMHO with the use of a
"required_emulation_flags" variable suitably initialised and then checked,
compared with the use of bitops etc.

> 
> Jan
> 
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