[SCSI] sd: Implement support for WRITE SAME

Implement support for WRITE SAME(10) and WRITE SAME(16) in the SCSI disk
driver.

 - We set the default maximum to 0xFFFF because there are several
   devices out there that only support two-byte block counts even with
   WRITE SAME(16). We only enable transfers bigger than 0xFFFF if the
   device explicitly reports MAXIMUM WRITE SAME LENGTH in the BLOCK
   LIMITS VPD.

 - max_write_same_blocks can be overriden per-device basis in sysfs.

 - The UNMAP discovery heuristics remain unchanged but the discard
   limits are tweaked to match the "real" WRITE SAME commands.

 - In the error handling logic we now distinguish between WRITE SAME
   with and without UNMAP set.

The discovery process heuristics are:

 - If the device reports a SCSI level of SPC-3 or greater we'll issue
   READ SUPPORTED OPERATION CODES to find out whether WRITE SAME(16) is
   supported. If that's the case we will use it.

 - If the device supports the block limits VPD and reports a MAXIMUM
   WRITE SAME LENGTH bigger than 0xFFFF we will use WRITE SAME(16).

 - Otherwise we will use WRITE SAME(10) unless the target LBA is beyond
   0xFFFFFFFF or the block count exceeds 0xFFFF.

 - no_write_same is set for ATA, FireWire and USB.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index da36a3a81a9..9032e910bca 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -900,11 +900,23 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 				action = ACTION_FAIL;
 				error = -EILSEQ;
 			/* INVALID COMMAND OPCODE or INVALID FIELD IN CDB */
-			} else if ((sshdr.asc == 0x20 || sshdr.asc == 0x24) &&
-				   (cmd->cmnd[0] == UNMAP ||
-				    cmd->cmnd[0] == WRITE_SAME_16 ||
-				    cmd->cmnd[0] == WRITE_SAME)) {
-				description = "Discard failure";
+			} else if (sshdr.asc == 0x20 || sshdr.asc == 0x24) {
+				switch (cmd->cmnd[0]) {
+				case UNMAP:
+					description = "Discard failure";
+					break;
+				case WRITE_SAME:
+				case WRITE_SAME_16:
+					if (cmd->cmnd[1] & 0x8)
+						description = "Discard failure";
+					else
+						description =
+							"Write same failure";
+					break;
+				default:
+					description = "Invalid command failure";
+					break;
+				}
 				action = ACTION_FAIL;
 				error = -EREMOTEIO;
 			} else