This patch enables xen event channels. It creates the placeholder for the
kernel evtchns when we move to OSv as well.
The main problem with this patch, is that evtchn::pending can return more than
one evtchn, so this that I am doing here is technically wrong. We should probably
call keep_doing() in pending() itself, and have that to store the references to
futures equivalent to the possible event channels, that would then be made ready.
I am, however, having a bit of a hard time coding this, since it's still
unclear how, once the future is consumed, we would generate the next.
Please note: All of this is moot if we disable "split event channels", which
can be done by masking that feature in case it is even available. In that case,
only one event channel will be notified, and when ready, we process both tx and
rx. This is yet another reason why I haven't insisted so much in fixing this properly
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
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