linux-kernel - Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME

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Date:	Wed, 16 Jul 2014 04:01:11 -0700
From:	"hch@...radead.org" <hch@...radead.org>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	KY Srinivasan <kys@...rosoft.com>,
	"hch@...radead.org" <hch@...radead.org>,
	James Bottomley <jbottomley@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"ohering@...e.com" <ohering@...e.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16

On Sun, Jul 13, 2014 at 08:58:34AM -0400, Martin K. Petersen wrote:
> >>>>> "KY" == KY Srinivasan <kys@...rosoft.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);
 	}
 
 	sdkp->capacity = lba + 1;
--
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