Re: [PATCH, RFC] virtio_blk: add cache flush command

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Am Tuesday 12 May 2009 15:54:14 schrieb Rusty Russell:
> On Mon, 11 May 2009 06:09:08 pm Christoph Hellwig wrote:
> > Do we need a new feature flag for this command or can we expect that
> > all previous barrier support was buggy enough anyway?
> 
> You mean reuse the VIRTIO_BLK_F_BARRIER for this as well?  Seems fine.
> 
> AFAIK only lguest offered that, and lguest has no ABI.  Best would be to 
> implement VIRTIO_BLK_T_FLUSH as well; it's supposed to be demo code, and it 
> should be easy).

It is also used by kuli (http://www.ibm.com/developerworks/linux/linux390/kuli.html)
and kuli used fdatasync. Since kuli is on offical webpages it takes a while
to update that code. When you reuse the VIRTIO_BLK_F_BARRIER flag, that would 
trigger some VIRTIO_BLK_T_FLUSH commands sent to the kuli host, right?
I think the if/else logic of kuli would interpret that as a read request....I 
am voting for a new feature flag :-)

Christian



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