FLIC (floating interrupt controller)
====================================

FLIC handles floating (non per-cpu) interrupts, i.e. I/O, service and some
machine check interruptions. All interrupts are stored in a per-vm list of
pending interrupts. FLIC performs operations on this list.

Only one FLIC instance may be instantiated.

FLIC provides support to
- add interrupts (KVM_DEV_FLIC_ENQUEUE)
- inspect currently pending interrupts (KVM_FLIC_GET_ALL_IRQS)
- purge all pending floating interrupts (KVM_DEV_FLIC_CLEAR_IRQS)

Groups:
  KVM_DEV_FLIC_ENQUEUE
    Passes a buffer and length into the kernel which are then injected into
    the list of pending interrupts.
    attr->addr contains the pointer to the buffer and attr->attr contains
    the length of the buffer.
    The format of the data structure kvm_s390_irq as it is copied from userspace
    is defined in usr/include/linux/kvm.h.

  KVM_DEV_FLIC_GET_ALL_IRQS
    Copies all floating interrupts into a buffer provided by userspace.
    When the buffer is too small it returns -ENOMEM, which is the indication
    for userspace to try again with a bigger buffer.
    All interrupts remain pending, i.e. are not deleted from the list of
    currently pending interrupts.
    attr->addr contains the userspace address of the buffer into which all
    interrupt data will be copied.
    attr->attr contains the size of the buffer in bytes.

  KVM_DEV_FLIC_CLEAR_IRQS
    Simply deletes all elements from the list of currently pending floating
    interrupts.  No interrupts are injected into the guest.