linux-kernel - Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus

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Message-ID: <4A48CF99.40002@redhat.com>
Date:	Mon, 29 Jun 2009 17:28:41 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	"Michael S. Tsirkin" <mst@...hat.com>,
	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	markmc@...hat.com
Subject: Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus

On 06/29/2009 05:06 PM, Marcelo Tosatti wrote:
> On Sun, Jun 28, 2009 at 10:34:25PM +0300, Michael S. Tsirkin wrote:
>    
>> This changes bus accesses to use high-level kvm_io_bus_read/kvm_io_bus_write
>> functions, which utilize read/write semaphore intead of mutex.  in_range now
>> becomes unused so it is removed from device ops in favor of read/write
>> callbacks performing range checks internally.
>>
>> This allows aliasing (mostly for in-kernel virtio), as well as better error
>> handling by making it possible to pass errors up to userspace. And it's enough
>> to look at the diffstat to see that it's a better API anyway.
>>      
>
> Can you please expand a little on this? Still don't get why making
> ->in_range part of ->read / ->write is a good thing. Aliasing?
>    

Yes, if you have several devices responding to the same port (but 
different values), in_range() by itself doesn't tell you much.  virtio 
msi support will tie a different iosignalfd to every queue, and queues 
are notified by writing different values to one pio port.

-- 
error compiling committee.c: too many arguments to function

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