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Re: [Xen-devel] code question?

To: Jerone Young <jyoung5@xxxxxxxxxx>
Subject: Re: [Xen-devel] code question?
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Thu, 11 Aug 2005 11:18:12 -0500
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Jerone Young wrote:

Doing some janitorial (you cleaning the flooded toilets and such) work
today. I have come across this line of code that really I'm not sure
what the intent was..in xen/include/sched.h

#define hypercall_preempt_check() (unlikely(            \
       softirq_pending(smp_processor_id()) |           \
       (!!current->vcpu_info->evtchn_upcall_pending &  \
         !current->vcpu_info->evtchn_upcall_mask)      \

the part where we have !!current->vcpu_info_evtchen_upcall pending
should this be..should the "!! just be "!"?
The usual use of !!a is to do (a != 0) ? 1 : 0.

I'm not sure if there's a more readable way to do it.


Anthony Liguori

And if so shouldn't this just be changed to
#define hypercall_preempt_check() (unlikely( \
        softirq_pending(smp_processor_id()) |           \
        (!(current->vcpu_info->evtchn_upcall_pending & \
          current->vcpu_info->evtchn_upcall_mask)) \

In a lot of the code in Xen we are using the "!" operator with bitwise
operations..this is one of those examples.

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