Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16

James Bottomley
2014-07-16T14:53:47Z

On Wed, 2014-07-16 at 04:01 -0700, hch@infradead.org wrote:
> On Sun, Jul 13, 2014 at 08:58:34AM -0400, Martin K. Petersen wrote:
> > >>>>> "KY" == KY Srinivasan <kys@microsoft.com> writes:
> >
> > KY> Windows hosts do support UNMAP and set the field in the
> > KY> EVPD. However, since the host advertises SPC-2 compliance, Linux
> > KY> does not even query the VPD page.
> >
> > >> If we want to enable UNMAP in this case I'd prefer a blacklist entry
> > >> than trying UNMAP despite the device not advertising it.
> >
> > I agree with that. We could do something like the patch below.
> >
> > However, I do think it's a good idea that you guys are looking into
> > reporting SPC-3.
>
> KY mentioned that they have a prototype for that now.
>
> Btw, I looked over sd.c a bit more, and I think I understand why they
> get the WRITE SAME commands now:
>
> read_capacity_16 calls sd_config_discard(sdkp, SD_LBP_WS16) if the LPBME
> bit is set. At least older SBC drafts left it wide open if a target
> supports WRITE SAME with UNMAP or UNMAP in this case. So I think we'd
> still want a patch to use UNMAP instead of WRITE SAME for this case,
> which should also fix hyperv. Below is the quick hack version of that
> that just checks the host no_write_same flag, as the one on the device
> isn't set yet - I guess we need to refactor some of that logic.
>
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 87566b5..4480fdf 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2035,7 +2035,10 @@ static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
> if (buffer[14] & 0x40) /* LBPRZ */
> sdkp->lbprz = 1;
>
> - sd_config_discard(sdkp, SD_LBP_WS16);
> + if (sdp->host->no_write_same)
> + sd_config_discard(sdkp, SD_LBP_UNMAP);
> + else
> + sd_config_discard(sdkp, SD_LBP_WS16);

Right, I already said this was the problem: that was the reason for my
patch. However, there are a couple of other cases (including the /sys
entry) which is why I patched sd_config_discard instead.

James