Re: [virtio] [PATCH] virtio-blk: restore VIRTIO_BLK_F_CONFIG_WCE (VIRTIO-144)

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jul 02, 2015 at 03:10:48PM +0200, Paolo Bonzini wrote:
> 
> 
> On 02/07/2015 13:21, James Bottomley wrote:
> > > +If the \field{VIRTIO_BLK_F_FLUSH} feature is not negotiated, the
> > > +device SHOULD ensure that all writes are committed to non-volatile
> > > +storage before reporting completion.  It MUST do so if it proposed
> > > +\field{VIRTIO_BLK_F_FLUSH}.  Failure to do so can cause data loss.
> >
> > Not SHOULD, MUST.  Please don't leave spec based doors open to bad
> > implementations.  An implementation that allows data corruption MUST NOT
> > have a spec interpretation that supports it.
> 
> What I'm trying to do is to make it possible for the guest to detect an
> implementation that is intentionally unsafe.  Such an implementation
> MUST NOT propose the VIRTIO_BLK_F_FLUSH feature, unlike the USB drives
> you mention.  I totally agree that WCE and FLUSH are not separable.
> 
> Paolo

Hmm. Very simple drivers don't negotiate any features.
Making such drivers lose data isn't a good idea I think.

-- 
MST