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Date: Mon, 15 Dec 2008 08:23:12 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Andrea Arcangeli <aarcange@redhat.com>, chrisw@redhat.com, kvm@vger.kernel.org, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>, Paul Brook <paul@codesourcery.com>

Anthony Liguori wrote:
>>
>> I Wouldn't be surprised if some machines had a large memory mapped IO 
>> space.  Most of it might not be actively used, but once you start 
>> considering 64-bit machines on 32-bit hosts these allocations would 
>> become problematic.
>>   
>
> At some level, any DMA API would fall apart here.  Certain IO 
> operations simply cannot be split (such as network send).  If you pass 
> don't pass a flag to the map function that says you can handle partial 
> results, you must cope with map() returning NULL (by dropping the 
> packet).
>

... and then you must cope with it.  In all non-network dma clients.  Or 
in the dma api.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.