Re: [virtio] [PATCH v5] virtio-blk: restore VIRTIO_BLK_F_FLUSH and VIRTIO_BLK_F_CONFIG_WCE

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

On Tue, Aug 11, 2015 at 03:53:03PM +0200, Paolo Bonzini wrote:
> 
> 
> On 11/08/2015 15:23, Michael S. Tsirkin wrote:
> > OK to summarize, how about:
> > 
> > In free text:
> > 
> > The cache mode after reset can be either writeback or writethrough.
> > The actual mode can be determined by reading \field{writeback}.
> 
> ... after feature negotiation.  Otherwise okay.
> 
> > In conformance paragraph:
> > 
> > The driver MUST NOT read \field{writeback} before setting
> > the FEATURES_OK \field{status} bit.
> 
> Okay.
> 
> > 
> > And in legacy section:
> > 
> > Legacy drivers and drivers did not support the FEATURES_OK \field{status} bit,
> > and used the device before setting the DRIVER_OK bit.
> > Therefore:
> > 
> > When using the legacy interface, the driver MAY read \field{writeback}
> > before setting the FEATURES_OK \field{status} field.
> > When using the legacy interface, the transitional devices MAY assume
> > that driver features won't be changed after reading \field{writeback}.
> 
> There is already a legacy section, so we can just add this there:
> 
> \item the driver MAY read or write \field{writeback} before setting the
> DRIVER or DRIVER_OK \field{status} bit
> 
> Paolo


Yes but the device needs to know the features to set it, right?
That's why I proposed "the transitional devices MAY assume
that driver features won't be changed".