Re: [Qemu-devel] [PATCH 0/2] irq: add get_gsi callback

[Paolo Bonzini]

On 23/04/2015 10:49, Eric Auger wrote:
> This series introduces a new callback function in IRQState, named
> get_gsi_cb. It is supposed to be populated by the interrupt controller
> and its role is to convert the interrupt controller pin number into
> the global system interrupt (gsi) number. The gsi is used when setting
> irqfd up.
> 
> With PCI there is a PCIINTxRoute bus lookup mechanism that enables to
> retrieve the gsi from the PCI host controller/bridge pin. The conversion
> is implemented by the PCI host controller. With platform devices, this
> conversion function is implemented by the interrupt controller.
> 
> Besides the callback member, a setter is introduced. First user is
> arm_gic_kvm. A public function wraps the callback, qemu_irq_get_gsi.
> 
> The first user of qemu_irq_get_gsi might be the VFIO platform device.
> This will come in the "KVM platform device passthrough" series.

I'm sorry, I cannot understand the point of this without seeing a user.

Why can't you just use a GHashTable?  This mustn't be a hot path, since
VFIO does all the signalling in the kernel via irqfds.

Paolo