[PATCH] scsi: sd: Implement blacklist option for WRITE SAME w/ UNMAP

["Martin K. Petersen" <martin.petersen@oracle.com>]

SBC-4 states:

  "A MAXIMUM UNMAP LBA COUNT field set to a non-zero value indicates the
   maximum number of LBAs that may be unmapped by an UNMAP command"

  "A MAXIMUM WRITE SAME LENGTH field set to a non-zero value indicates
   the maximum number of contiguous logical blocks that the device server
   allows to be unmapped or written in a single WRITE SAME command."

Despite the spec being clear on the topic, some devices incorrectly
expect WRITE SAME commands with the UNMAP bit set to be limited to the
value reported in MAXIMUM UNMAP LBA COUNT in the Block Limits VPD.

Implement a blacklist option that can be used to accommodate devices
with this behavior.

Reported-by: Bill Kuzeja <William.Kuzeja@stratus.com>
Reported-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 drivers/scsi/scsi_scan.c    |  3 +++
 drivers/scsi/sd.c           | 16 ++++++++++++----
 include/scsi/scsi_device.h  |  1 +
 include/scsi/scsi_devinfo.h |  1 +
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index e7818afeda2b..15590a063ad9 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -956,6 +956,9 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
 	if (*bflags & BLIST_NO_DIF)
 		sdev->no_dif = 1;
 
+	if (*bflags & BLIST_UNMAP_LIMIT_WS)
+		sdev->unmap_limit_for_ws = 1;
+
 	sdev->eh_timeout = SCSI_DEFAULT_EH_TIMEOUT;
 
 	if (*bflags & BLIST_TRY_VPD_PAGES)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b18ba3235900..347be7580181 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -715,13 +715,21 @@ static void sd_config_discard(struct scsi_disk *sdkp, unsigned int mode)
 		break;
 
 	case SD_LBP_WS16:
-		max_blocks = min_not_zero(sdkp->max_ws_blocks,
-					  (u32)SD_MAX_WS16_BLOCKS);
+		if (sdkp->device->unmap_limit_for_ws)
+			max_blocks = sdkp->max_unmap_blocks;
+		else
+			max_blocks = sdkp->max_ws_blocks;
+
+		max_blocks = min_not_zero(max_blocks, (u32)SD_MAX_WS16_BLOCKS);
 		break;
 
 	case SD_LBP_WS10:
-		max_blocks = min_not_zero(sdkp->max_ws_blocks,
-					  (u32)SD_MAX_WS10_BLOCKS);
+		if (sdkp->device->unmap_limit_for_ws)
+			max_blocks = sdkp->max_unmap_blocks;
+		else
+			max_blocks = sdkp->max_ws_blocks;
+
+		max_blocks = min_not_zero(max_blocks, (u32)SD_MAX_WS10_BLOCKS);
 		break;
 
 	case SD_LBP_ZERO:
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 82e93ee94708..67c5a9f223f7 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -192,6 +192,7 @@ struct scsi_device {
 	unsigned no_dif:1;	/* T10 PI (DIF) should be disabled */
 	unsigned broken_fua:1;		/* Don't set FUA bit */
 	unsigned lun_in_cdb:1;		/* Store LUN bits in CDB[1] */
+	unsigned unmap_limit_for_ws:1;	/* Use the UNMAP limit for WRITE SAME */
 
 	atomic_t disk_events_disable_depth; /* disable depth for disk events */
 
diff --git a/include/scsi/scsi_devinfo.h b/include/scsi/scsi_devinfo.h
index 9592570e092a..36b03013d629 100644
--- a/include/scsi/scsi_devinfo.h
+++ b/include/scsi/scsi_devinfo.h
@@ -29,5 +29,6 @@
 #define BLIST_TRY_VPD_PAGES	0x10000000 /* Attempt to read VPD pages */
 #define BLIST_NO_RSOC		0x20000000 /* don't try to issue RSOC */
 #define BLIST_MAX_1024		0x40000000 /* maximum 1024 sector cdb length */
+#define BLIST_UNMAP_LIMIT_WS	0x80000000 /* Use UNMAP limit for WRITE SAME */
 
 #endif
-- 
2.14.1