Xen devel - Feb 2005 - Question about event channels and masking event channels

Hello,

There is something I do not undestand about the event handling
mechanism in xenolinux.
XenoLinux can listen for 1024 events (0 to 1023). The shared_info_t
structure records the pending and the masking of events using the
following bit vectors:
================================================u32 evtchn_pending[32]; 
u32 evtchn_pending_sel; 
u32 evtchn_mask[32]; 
================================================
Next, I am looking at the function mask_evtchn() in the file evtchn.h
================================================static inline void
mask_evtchn(int port)
{
    shared_info_t *s = HYPERVISOR_shared_info;
    synch_set_bit(port, &s->evtchn_mask[0]);
}
================================================
Why do we only focus on evtchn_mask[0] ?
I thought that Port would be a number between 0 to 1023 and masking
the correct bit would be done with something like that:
synch_set_bit(port%32, &s->evtchn_mask[port/32]);

Is it the case that one can only mask out the first 8 bits in evtchn_mask[0] ?

Thanks
Rick


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I''m guessing that sync_set_bit requires a bit number, and a pointer to
a
bit array of some type.

The &s->evtchn_mask[0] is effectively the same as s->evtchn_mask,
however it results in a different pointer type (only really important
for the compiler).

So synch_set_bit is passed a pointer to the array, so that it an perform
the appropriate operation (I''m guessing again) synchronised.

Scott.

Rick wrote:
>Hello,
>
>There is something I do not undestand about the event handling
>mechanism in xenolinux.
>XenoLinux can listen for 1024 events (0 to 1023). The shared_info_t
>structure records the pending and the masking of events using the
>following bit vectors:
>================================================>u32 evtchn_pending[32]; 
>u32 evtchn_pending_sel; 
>u32 evtchn_mask[32]; 
>================================================>
>Next, I am looking at the function mask_evtchn() in the file evtchn.h
>================================================>static inline void
mask_evtchn(int port)
>{
>    shared_info_t *s = HYPERVISOR_shared_info;
>    synch_set_bit(port, &s->evtchn_mask[0]);
>}
>================================================>
>Why do we only focus on evtchn_mask[0] ?
>I thought that Port would be a number between 0 to 1023 and masking
>the correct bit would be done with something like that:
>synch_set_bit(port%32, &s->evtchn_mask[port/32]);
>
>Is it the case that one can only mask out the first 8 bits in evtchn_mask[0]
?
>
>Thanks
>Rick
>
>
>-------------------------------------------------------
>SF email is sponsored by - The IT Product Guide
>Read honest & candid reviews on hundreds of IT Products from real users.
>Discover which products truly live up to the hype. Start reading now.
>http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.sourceforge.net
>https://lists.sourceforge.net/lists/listinfo/xen-devel
>
>  
>



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Discover which products truly live up to the hype. Start reading now.
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