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

Christian Borntraeger
2009-05-12T14:18:39Z

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