target: Enforce hw_max_sectors for SCF_SCSI_DATA_SG_IO_CDB

Instead of depending upon a max_sectors value that may be set via
configfs based upon original HW queue limitations, go ahead and convert to using
the hw_max_sectors reported by the backend device in order to determine when
to reject an I/O's who's sector count exceeds what is supported by the backend
with a single se_cmd descriptor.

It addresses a potential case where se_dev_attrib.max_sectors for IBLOCK
backends has already been set via queue_max_sectors() to something small
like max_sectors=32 (LVM, DRBD may do this), resulting typically sized
SCF_SCSI_DATA_SG_IO_CDB to be incorrectly rejected with invalid_cdb_field
in transport_generic_cmd_sequencer().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -2973,12 +2973,21 @@ static int transport_generic_cmd_sequencer(
 		cmd->data_length = size;
 	}
 
-	if (cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB &&
-	    (sectors > dev->se_sub_dev->se_dev_attrib.fabric_max_sectors ||
-	     sectors > dev->se_sub_dev->se_dev_attrib.max_sectors)) {
-		printk_ratelimited(KERN_ERR "SCSI OP %02xh with too big sectors %u\n",
-				   cdb[0], sectors);
-		goto out_invalid_cdb_field;
+	if (cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB) {
+		if (sectors > su_dev->se_dev_attrib.fabric_max_sectors) {
+			printk_ratelimited(KERN_ERR "SCSI OP %02xh with too"
+				" big sectors %u exceeds fabric_max_sectors:"
+				" %u\n", cdb[0], sectors,
+				su_dev->se_dev_attrib.fabric_max_sectors);
+			goto out_invalid_cdb_field;
+		}
+		if (sectors > su_dev->se_dev_attrib.hw_max_sectors) {
+			printk_ratelimited(KERN_ERR "SCSI OP %02xh with too"
+				" big sectors %u exceeds backend hw_max_sectors:"
+				" %u\n", cdb[0], sectors,
+				su_dev->se_dev_attrib.hw_max_sectors);
+			goto out_invalid_cdb_field;
+		}
 	}
 
 	/* reject any command that we don't have a handler for */