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SubjectRe: [PATCH v7 2/2] kvm: KVM_EOIFD, an eventfd for EOIs
On 07/24/2012 11:43 PM, Alex Williamson wrote:
> This new ioctl enables an eventfd to be triggered when an EOI is
> written for a specified irqchip pin. The first user of this will
> be external device assignment through VFIO, using a level irqfd
> for asserting a PCI INTx interrupt and this interface for de-assert
> and notification once the interrupt is serviced.
> Here we make use of the reference counting of the _irq_source
> object allowing us to share it with an irqfd and cleanup regardless
> of the release order.

The name is slightly misleading. eoifd doesn't trigger on EOI (which is
an APIC->IOAPIC interface) but rather when an interrupt controller
resamples an input line. This happens for the IOAPIC when an EOI is
received for a vector that is configured for level interrupts and not
masked, or similarly for a PIC (but this is not triggered by an APIC EOI).

It's not a huge difference, but let's document it.

> +4.77 KVM_EOIFD
> +
> +Capability: KVM_CAP_EOIFD
> +Architectures: x86
> +Type: vm ioctl
> +Parameters: struct kvm_eoifd (in)
> +Returns: 0 on success, < 0 on error
> +
> +KVM_EOIFD allows userspace to receive interrupt EOI notification
> +through an eventfd. kvm_eoifd.fd specifies the eventfd used for
> +notification. KVM_EOIFD_FLAG_DEASSIGN is used to de-assign an eoifd
> +once assigned. KVM_EOIFD also requires additional bits set in
> +kvm_eoifd.flags to bind to the proper interrupt line. The
> +KVM_EOIFD_FLAG_LEVEL_IRQFD indicates that kvm_eoifd.key is provided
> +and is a key from a level triggered interrupt (configured from
> +KVM_IRQFD using KVM_IRQFD_FLAG_LEVEL). The EOI notification is bound
> +to the same GSI and irqchip input as the irqfd. Both kvm_eoifd.key
> +and KVM_EOIFD_FLAG_LEVEL_IRQFD must be specified on assignment and
> +de-assignment of KVM_EOIFD. A level irqfd may only be bound to a
> +single eoifd. KVM_CAP_EOIFD_LEVEL_IRQFD indicates support of

Why do we need to couple eoifd and irqfd?

error compiling committee.c: too many arguments to function

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