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

[Christoph Hellwig <hch@lst.de>]

On Tue, May 12, 2009 at 04:18:36PM +0200, Christian Borntraeger wrote:
> 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 :-)

Ok, next version will have a new feature flag.  I actually have some
other bits I want to redesign so it might take a bit longer to get it
out.