Re: ZBC_IN command translation

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 07, 2017 at 06:03:52PM +0900, Damien Le Moal wrote:
> Tejun, Hannes,
> 
> Currently, in libata-scsi.c, the function ata_scsi_zbc_in_xlat
> translating ZBC REPORT ZONES into the ZAC version returns an error if
> the scsi command buffer length is not aligned on 512. This is possible
> since the ZBC version allows report zones buffer as a multiple of 64B,
> while the ZAC version of the same command requires 512B size alignment
> of the command buffer.
> 
> However, SAT-4, in section 9.13.3 says:
> 
> "The SATL shall send the ATA REPORT ZONES EXT command with the ATA
> RETURN PAGE COUNT field set to INT((ALLOCATION LENGTH + 511)/512)."
> 
> So clearly, instead of returning an error, we need to bounce the scsi
> command buffer to a bigger 512B size aligned temporary buffer for the
> ZAC report zones. I do not see any code ready to use to do so easily,
> but I may be missing it. Is there something that can be used to do so or
> do I need to cook something ?

Just like for TRIM we should reject any ZBC_IN/OUT command that doesn't
come from the block layer, and then we can tightly control what input
we get.