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Date: Sun, 15 Mar 2009 15:43:13 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH 1/3] Add specialized block driver
	scsi	generic API
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To: qemu-devel@nongnu.org

On Sun, Mar 15, 2009 at 03:54:26PM +0200, Avi Kivity wrote:
> >Hower the way the new
> >API is designed somewhat gets in the way of my patch series to support
> >Gerd's native preadv/pwritev.
> >
> >  
> 
> Can you point out specific issues?

The patch series (now posted) makes all aio APIs use iovecs.  The
current non-iovec based SG API would require some nasty shims allocating
nested aiocbs.  Or we could just make the sg aio methods fake-ioveced
which is the solution I had before your split, always adding a
one-element iovec to the scsi-generic request structure.


> Using the block layer has the advantage of common setup, statistics, and 
> management.  I agree that the actual data movement is horribly out of 
> sync with the other format drivers.

Yeah, the setup is kinda interwinded with the block layer.  I wonder
whether the device-tree ideas will help sorting that out.

Note that I eventually want to support SG_IO on cdrom devices for
burning etc at which point we need to support scsi-generic even
if another driver is attached.  Note entirely sure how to handle
that yet.