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Date: Sun, 15 Mar 2009 08:20:00 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 2/6] change vectored block I/O API to plain
	iovecs
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To: qemu-devel@nongnu.org

Avi Kivity wrote:
> Christoph Hellwig wrote:
>> QEMUIOVector is a useful helper for the dma-helper.c internals but 
>> for a generic
>> block API it's more of hindrance.  Some top-level consumers like 
>> virtio-blk
>> already have the plain iovec and segment number at hand and can pass 
>> it down
>> directly, and for those that just have a single element and need to 
>> fake up
>> a vector the plain iovec also is a lot easier.
>>   
>
> virtio gets its iovecs through a hacky (and incorrect, try >=4G) 
> method.  IMO virtio should be fixed to use the dma api, at which point 
> it will start to use QEMUIOVector anyway,

 >= 4GB should work fine in virtio.  It basically replicates the DMA API 
today.  It doesn't handle MMIO memory though.

>> Last but not leas we want to push down vectored I/O to the lowest level,
>> and if posix-aio-compat.c wants to stay somewhat true to it's goal of
>> beeing like an ehanced posix AIO API it should stick to posix types.
>>   
>
> Internally yes, but why should bdrv_* not use QEMUIOVector?  That API 
> isn't very interested in posix.

Agreed.

Regards,

Anthony Liguori