Gregory Haskins wrote:
This allows an eventfd to be registered as an irq source with a
guest. Any
signaling operation on the eventfd (via userspace or kernel) will inject
the registered GSI at the next available window.
+struct kvm_irqfd {
+ __u32 fd;
+ __u32 gsi;
+};
+
I think it's better to have ioctl create and return the fd. This way
we aren't tied to eventfd (though it makes a lot of sense to use it).
I dont mind either way, but I am not sure it buys us much as the one
driving the fd would need to understand if the interface is
eventfd-esque or something else anyway. Let me know if you still want
to see this changed.
Sure, the interface remains the same (write 8 bytes), but the
implementation can change. For example, we can implement it to work
from interrupt context, once we hack the locking appropriately.
+static void
+irqfd_inject(struct work_struct *work)
+{
+ struct _irqfd *irqfd = container_of(work, struct _irqfd, work);
+ struct kvm *kvm = irqfd->kvm;
+
+ mutex_lock(&kvm->lock);
+ kvm_set_irq(kvm, kvm->irqfd.src, irqfd->gsi, 1);
Need to lower the irq too (though irqfd only supports edge triggered
interrupts).
Should I just do back-to-back 1+0 inside the same lock?
Yes. Might be nice to add a kvm_toggle_irq(), but let's leave that
until later.
One day we'll have lockless injection and we'll want to drop this. I
guess if we create the fd ourselves we can make it work, but I don't
see how we can do this with eventfd.
Hmm...this is a good point. There probably is no way to use eventfd
"off the shelf" in a way that doesn't cause this callback to be in a
critical section. Should we just worry about switching away from
eventfd when this occurs, or should I implement a custom anon-fd now?
I'd just go with eventfd, and switch when it becomes relevant. As long
as the kernel allocates the fd, we're free to do as we like.
--
error compiling committee.c: too many arguments to function
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