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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? > 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.
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