On Wed, 26 Aug 2009, Avi Kivity wrote:
> On 08/26/2009 08:45 PM, Davide Libenzi wrote:
> > OK, if I get it correctly, there is one eventfd signaler (the device), and
> > one eventfd reader (the hypervisor), right?
> > Each hypervisor listens for multiple devices detecting state changes, and
> > associating the eventfd "line" to the IRQ number by some configuration
> > (ala PCI), right?
> >
>
> Yes. The PCI stuff happens in userspace, all the hypervisor sees is "this
> eventfd is IRQ 10". There may be multiple eventfds routed to one IRQ
> (corresponding to a shared IRQ line).
Ok, so why not using the eventfd counter as state?
On the device side:
void write_state(int sfd, int state) {
u64 cnt;
/* Clear the current state, sfd is in non-blocking mode */
read(sfd, &cnt, sizeof(cnt));
/* Writes new state */
cnt = 1 + !!state;
write(sfd, &cnt, sizeof(cnt));
}
On the hypervisor side:
int read_state(int sfd) {
u64 cnt;
read(sfd, &cnt, sizeof(cnt));
return state - 1;
}
- Davide
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