Hypervisor interfaces need to be negotiated in order to use
some API calls reliably. So add a small set of interfaces
to request API versions and query current settings.
This allows us to fix some bugs in the hypervisor console:
1) If we can negotiate API group CORE of at least major 1
minor 1 we can use con_read and con_write which can improve
console performance quite a bit.
2) When we do a console write request, we should hold the
spinlock around the whole request, not a byte at a time.
What would happen is that it's easy for output from
different cpus to get mixed with each other.
3) Use consistent udelay() based polling, udelay(1) each
loop with a limit of 1000 polls to handle stuck hypervisor
console.
Signed-off-by: David S. Miller <davem@davemloft.net>
