linux-kernel - Re: [KVM PATCH v7 2/3] kvm: add support for irqfd via eventfd-notification interface

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Message-ID: <4A0C18D3.6060905@gmail.com>
Date:	Thu, 14 May 2009 09:12:51 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	viro@...IV.linux.org.uk, linux-kernel@...r.kernel.org,
	davidel@...ilserver.org
Subject: Re: [KVM PATCH v7 2/3] kvm: add support for irqfd via	eventfd-notification
 interface

Avi Kivity wrote:
> Gregory Haskins wrote:
>>> Please fget() the new fd and compare the filps; fds aren't meaningful
>>> in the kernel.  You can also drop _irqfd::fd.
>>>     
>>
>> I like this as a second option...
>>
>>  
>>> It may also be useful to compare the gsi, this allows a
>>> "make-before-break" switchover:
>>>     
>>
>> ...but I like this best.  Good idea.
>>   
>
> I thought of comparing both.

Ah, ok.  I misunderstood.  We can do that.
>
>>> - guest reroutes irq to a different gsi
>>> - associate irqfd with new gsi
>>> - disassociate irqfd from old gsi
>>>
>>>    
>>>> +
>>>> +        irqfd_release(irqfd);
>>>> +        mutex_unlock(&kvm->lock);
>>>> +        return 0;
>>>>         
>>> Don't return, userspace may have multiple associations?
>>>     
>>
>> Parse error.  Can you elaborate?
>>
>>   
>
> You break out of the look when you match your irqfd.  But there may be
> multiple matches.
>
> Granted, it doesn't make much sense to hook the same fd to the same
> gsi multiple times (it may make sense to hook multiple fds to a single
> gsi, or maybe a single fd to multiple gsis), but it pays to have a
> consistent do-what-I-said-even-if-it-doesn't-make-sense interface.

Ack, will do.

-Greg



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