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, 02 Jun 2009 13:42:02 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Davide Libenzi <davidel@...ilserver.org>
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

Davide Libenzi wrote:
> 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
>
>
>   
Indeed.  Thanks for catching that!

-Greg


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