Re: [Nbd] write_zeroes/trim on the whole disk

[Vladimir Sementsov-Ogievskiy <vsementsov@...2319...>]

On 24.09.2016 16:42, Vladimir Sementsov-Ogievskiy wrote:
> On 24.09.2016 15:06, Vladimir Sementsov-Ogievskiy wrote:
> > On 24.09.2016 00:21, Wouter Verhelst wrote:
> > > On Fri, Sep 23, 2016 at 02:00:06PM -0500, Eric Blake wrote:
> > > > My preference would be a new flag to the existing commands, with
> > > > explicit documentation that 0 offset and 0 length must be used with 
> > > > that
> > > > flag, when requesting a full-device wipe.
> > > Alternatively, what about a flag that says "if you use this flag, the
> > > size should be left-shifted by X bits before processing"? That allows
> > > you to do TRIM or WRITE_ZEROES on much larger chunks, without being
> > > limited to "whole disk" commands. We should probably make it an illegal
> > > flag for any command that actually sends data over the wire, though.
> >
> >
> > Note: if disk size is not aligned to X we will have to send request 
> > larger than the disk size to clear the whole disk.
>
> which is not beautiful.. And splitting the request into two: 
> (disk_size / X * X) and (disk_size % X) is not beautiful too. May be 
> flag, that says 'whole disk request' is more appropriate? Nothing 
> prevents adding then flag about X-shift.

Also, accordingly to documentation, NBD_CMD_TRIM is not appropriate for 
disk clearing:

  * `NBD_CMD_TRIM` (4)

      A hint to the server that the data defined by len and offset is no
      longer needed. A server MAY discard len bytes starting at offset, but
      is not required to.

      After issuing this command, a client MUST NOT make any assumptions
      about the contents of the export affected by this command, until
      overwriting it again with `NBD_CMD_WRITE`.

- it may do nothing.. So, what to do with this? add flag FORCE_TRIM for 
this command? Or add FORCE_HOLES flag to WRITE_ZEROES?


--
Best regards,
Vladimir