RE: [RFC v2] virtio-blk: add discard and write zeroes features to specification

["Liu, Changpeng" <changpeng.liu@intel.com>]

> -----Original Message-----
> From: Stefan Hajnoczi [mailto:stefanha@redhat.com]
> Sent: Monday, March 5, 2018 7:34 PM
> To: Liu, Changpeng <changpeng.liu@intel.com>
> Cc: virtio-dev@lists.oasis-open.org; cavery@redhat.com; pbonzini@redhat.com;
> Wodkowski, PawelX <pawelx.wodkowski@intel.com>; Harris, James R
> <james.r.harris@intel.com>
> Subject: Re: [RFC v2] virtio-blk: add discard and write zeroes features to
> specification
> 
> On Wed, Feb 28, 2018 at 02:54:28PM +0800, Changpeng Liu wrote:
> > @@ -4211,6 +4227,17 @@ according to the native endian of the guest rather
> than
> >    after reset can be either writeback or writethrough.  The actual
> >    mode can be determined by reading \field{writeback} after feature
> >    negotiation.
> > +
> > +\item If the VIRTIO_BLK_F_DISCARD feature is negotiated,
> > +    \field{max_discard_sectors} and \field{max_discard_seg} can be read
> > +    to determine the maximum discard sectors and maximum number of
> discard
> > +    segments for the block driver to use. \field{discard_sector_alignment}
> > +    can be used by OS when splitting a request based on alignment.
> > +
> > +\item if the VIRTIO_BLK_F_WRITE_ZEROES feature is negotiated,
> > +    \field{max_write_zeroes_sectors} and \field{max_write_zeroes_seg} can
> > +    be read to determine the maximum write zeroes sectors and maximum
> > +    number of write zeroes segments for the block driver to use.
> 
> Does "sectors" use the same 512-byte units as the capacity field?  The
> term "sectors" is slightly ambiguous in this spec so it would be helpful
> to describe it explicitly.
> 
> What are the units of discard_sector_alignment?
Ok, will add explicit unit description for those parameters in configuration space.
> 
> >  The \field{sector} number indicates the offset (multiplied by 512) where
> >  the read or write is to occur. This field is unused and set to 0
> >  for scsi packet commands and for flush commands.
> >
> > +The \field{sector} number indicates the offset (multiplied by 512) where
> > +the read or write is to occur. This field is unused and set to 0 for
> > +commands other than read or write.
> 
> This paragraph has been duplicated.
Thanks, will remove the duplicated paragraph.