scsi: core: Log SCSI command age with errors

Couple of users had requested to print the SCSI command age along with
command failure errors. This is a small change, but allows users to get
more important information about the command that was failed, it would help
the users in debugging the command failures:

Link: https://lore.kernel.org/r/20190926052501.GA8352@machine1
Signed-off-by: Milan P. Gandhi <mgandhi@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_logging.c

@@ -390,6 +390,7 @@ void scsi_print_result(const struct scsi_cmnd *cmd, const char *msg,
 	const char *mlret_string = scsi_mlreturn_string(disposition);
 	const char *hb_string = scsi_hostbyte_string(cmd->result);
 	const char *db_string = scsi_driverbyte_string(cmd->result);
+	unsigned long cmd_age = (jiffies - cmd->jiffies_at_alloc) / HZ;
 
 	logbuf = scsi_log_reserve_buffer(&logbuf_len);
 	if (!logbuf)
@@ -431,10 +432,15 @@ void scsi_print_result(const struct scsi_cmnd *cmd, const char *msg,
 
 	if (db_string)
 		off += scnprintf(logbuf + off, logbuf_len - off,
-				 "driverbyte=%s", db_string);
+				 "driverbyte=%s ", db_string);
 	else
 		off += scnprintf(logbuf + off, logbuf_len - off,
-				 "driverbyte=0x%02x", driver_byte(cmd->result));
+				 "driverbyte=0x%02x ",
+				 driver_byte(cmd->result));
+
+	off += scnprintf(logbuf + off, logbuf_len - off,
+			 "cmd_age=%lus", cmd_age);
+
 out_printk:
 	dev_printk(KERN_INFO, &cmd->device->sdev_gendev, "%s", logbuf);
 	scsi_log_release_buffer(logbuf);