Re: code question?

[Anthony Liguori <aliguori@us.ibm.com>]

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.

Regards,

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.
>
>
>
>  
>