Re: [Xen-devel] Question about event channels and masking event channels

[Scott Mohekey <smohekey@xxxxxxxxxxxxxxxx>]

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
>
>
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