linux-kernel - Re: [KVM-RFC PATCH 2/2] kvm: use POLLHUP to close an irqfd instead of an explicit ioctl

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Date:	Tue, 2 Jun 2009 10:16:01 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com, mst@...hat.com, paulmck@...ux.vnet.ibm.com
Subject: Re: [KVM-RFC PATCH 2/2] kvm: use POLLHUP to close an irqfd instead
 of an explicit ioctl

On Tue, 2 Jun 2009, Gregory Haskins wrote:

> @@ -64,12 +101,28 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
>  {
>  	struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
>  
> -	/*
> -	 * The wake_up is called with interrupts disabled.  Therefore we need
> -	 * to defer the IRQ injection until later since we need to acquire the
> -	 * kvm->lock to do so.
> -	 */
> -	schedule_work(&irqfd->work);
> +	switch ((unsigned long)key) {
> +	case POLLIN:
> +		/*
> +		 * The POLLIN wake_up is called with interrupts disabled.
> +		 * Therefore we need to defer the IRQ injection until later
> +		 * since we need to acquire the kvm->lock to do so.
> +		 */
> +		schedule_work(&irqfd->inject);
> +		break;
> +	case POLLHUP:
> +		/*
> +		 * The POLLHUP is called unlocked, so it theoretically should
> +		 * be safe to remove ourselves from the wqh
> +		 */
> +		remove_wait_queue(irqfd->wqh, &irqfd->wait);
> +		flush_work(&irqfd->inject);
> +		irqfd_disconnect(irqfd);
> +
> +		cleanup_srcu_struct(&irqfd->srcu);
> +		kfree(irqfd);
> +		break;
> +	}

Since "key" is an event *bitmap*, you better be treating it as such. Do 
not assume what eventfd delivers today (event bitmaps with only one bit 
set). So this better be like:

	if (key & POLLIN) {
		...
	}
	if (key & POLLHUP) {
		...
	}


- Davide


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