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Message-ID: <4AB980E6.2070203@codemonkey.ws>
Date: Tue, 22 Sep 2009 20:59:02 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [PATCH] qemu: make virtio-blk PCI compliant
	by	default
References: <20090907181436.GA8538@redhat.com>	<4AA60A58.4090703@redhat.com>	<20090908075831.GA9875@redhat.com>	<200909212039.01126.rusty@rustcorp.com.au>	<4AB7A01A.3000206@redhat.com>
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To: john cooper <john.cooper@redhat.com>
Cc: qemu-devel@nongnu.org, jens.axboe@oracle.com, Rusty Russell <rusty@rustcorp.com.au>, Avi Kivity <avi@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

john cooper wrote:
> Avi Kivity wrote:
>   
>> On 09/22/2009 05:21 PM, john cooper wrote:
>>     
>>>> Can we just read this page as a virtqueue command instead of having it
>>>> mapped permanently?
>>>>      
>>>>         
>>> Probably although I hadn't looked specifically
>>> at doing so.   Mapping the data via an unused
>>> pci bar is pretty trivial and seemed minimally
>>> intrusive to the existing driver.
>>>    
>>>       
>> We'll run out of bars if we expend them like that.
>>     
>
> Agreed.  However my motivation here was to use a
> single additional bar specifically to compensate
> for the PCI spec imposed 256 byte size limitation
> of the config space mapping.  As we're defining the
> content/size of this area, future use to accommodate
> additional data should be unrestricted.
>   

Why expose the whole ATAPI page instead of just the serial number?

I think the proper solution is to move the config to a separate bar 
that's MMIO instead of PIO.  config access is never performance 
sensitive and an MMIO bar has less restrictions on size.

Regards,

Anthony Liguori