[block] Retry reopening indefinitely for multipath devices

For multipath SAN devices, verify that the device is capable of being
opened (i.e. that all URIs are parseable and that at least one path is
alive) and thereafter retry indefinitely to reopen the device as
needed.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/sanboot.c

 			/* Delay reopening attempts */
 			sleep_fixed ( SAN_REOPEN_DELAY_SECS );
 
+			/* Retry opening indefinitely for multipath devices */
+			if ( sandev->paths <= 1 )
+				retries++;
+
 			continue;
 		}
 
 		/* Initiate command */
-		if ( ( rc = command ( sandev, params ) ) != 0 )
+		if ( ( rc = command ( sandev, params ) ) != 0 ) {
+			retries++;
 			continue;
+		}
 
 		/* Start expiry timer */
 		start_timer_fixed ( &sandev->timer, SAN_COMMAND_TIMEOUT );
 			step();
 
 		/* Check command status */
-		if ( ( rc = sandev->command_rc ) != 0 )
+		if ( ( rc = sandev->command_rc ) != 0 ) {
+			retries++;
 			continue;
+		}
 
 		return 0;
 
-	} while ( ++retries <= san_retries );
+	} while ( retries <= san_retries );
 
 	/* Sanity check */
 	assert ( ! timer_running ( &sandev->timer ) );
 		return -EADDRINUSE;
 	}
 
+	/* Check that device is capable of being opened (i.e. that all
+	 * URIs are well-formed and that at least one path is
+	 * working).
+	 */
+	if ( ( rc = sandev_reopen ( sandev ) ) != 0 )
+		return rc;
+
 	/* Read device capacity */
 	if ( ( rc = sandev_command ( sandev, sandev_command_read_capacity,
 				     NULL ) ) != 0 )