Re: [Xen-devel] [PATCH 11/16] x86/monitor: fix: treat -monitor- properly, as a subsys of the vm-event subsys

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

On 7/11/2016 7:38 PM, Tamas K Lengyel wrote:
> > > > diff --git a/xen/include/asm-arm/monitor.h
> > > > b/xen/include/asm-arm/monitor.h
> > > > index 9a9734a..7ef30f1 100644
> > > [snip]
> > I keep seeing '[snip]' lately but I don't know what it means.
> Placeholder for "I've cut some of your patch content here to shorten
> the message I'm sending".
>
> > > > diff --git a/xen/include/xen/monitor.h b/xen/include/xen/monitor.h
> > > > index 2171d04..605caf0 100644
> > > > --- a/xen/include/xen/monitor.h
> > > > +++ b/xen/include/xen/monitor.h
> > > > @@ -22,12 +22,15 @@
> > > >    #ifndef __XEN_MONITOR_H__
> > > >    #define __XEN_MONITOR_H__
> > > >
> > > > -#include <public/vm_event.h>
> > > > -
> > > > -struct domain;
> > > > -struct xen_domctl_monitor_op;
> > > > +#include <xen/sched.h>
> > > >
> > > >    int monitor_domctl(struct domain *d, struct xen_domctl_monitor_op *op);
> > > > +
> > > > +static inline bool_t monitor_domain_initialised(const struct domain *d)
> > > > +{
> > > > +    return d->monitor.initialised;
> > > This should be !!d->monitor.initialised.
> > It's the value of a bit, thus should be 0 or 1. Am I missing something?
> Using a bitfield is effectively doing a bitmask for the bit(s).
> However, returning the value after applying a bitmask is not
> necessarily 0/1 (ie. bool_t). For example I ran into problems with
> this in the past (see
> https://lists.xen.org/archives/html/xen-devel/2015-08/msg01948.html).
>
> Tamas
The example you provided actually returns a value &-ed with a flag 
(bitmask), of course it returns either 0 or the flag itself :-). AFAIK a 
single-bit item in a bitfield (note a -bitfield-, not e.g. an unsigned 
int &-ed with (1<<x)) will always be either 0 or 1.
Corneliu.

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