Re: [Qemu-devel] [PATCH] honor IDE_DMA_BUF_SECTORS

[Avi Kivity <avi@redhat.com>]

Samuel Thibault wrote:
> Avi Kivity, le Thu 26 Mar 2009 14:58:55 +0200, a écrit :
>   
>> Samuel Thibault wrote:
>>     
>>> Avi Kivity, le Thu 26 Mar 2009 14:10:20 +0200, a écrit :
>>>  
>>>       
>>>> I realize your use case will probably not trigger this, but it does 
>>>> indicate you're limiting at the wrong layer.  It places the burden on 
>>>> all callers of block format drivers instead of centralizing it.
>>>>    
>>>>         
>>> Then it should be centralized in the block layer instead of placing the
>>> burden on all block format drivers ;)
>>>  
>>>       
>> If other drivers need to do that, certainly.
>>     
>
> In our case the other driver is specific to Xen.
>   

I'm confused.  I can only count one driver which has limited dma size.

>   
>>> One thing for instance that still have been overlooked although patches
>>> have been sent is block-raw-posix' read/write_pread_aligned() that
>>> consider partial read/writes as an error.  That's a bug.
>>>  
>>>       
>> Right.  Unrelated topic though?
>>     
>
> Nope.  It's exactly the issue: read/write() may not be able to perform
> the whole operation in just one go, and qemu should continue in that
> case.
>   

Oh, you're overloading block-raw-posix?  Isn't it more natural for you 
to implement block-raw-xen-pv-block-frontend?  You'd be able to use 
asynchronous requests instead of a thread pool (much like 
block-raw-linux-aio).


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