isotp: support Linux 5.18 features

- update isotp.h include file
- update maximum PDU (buffer) size to 64kByte buffer
- support setting of N_As (frame_txtime) to zero

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

include/linux/can/isotp.h

@@ -137,20 +137,16 @@ struct can_isotp_ll_options {
 #define CAN_ISOTP_WAIT_TX_DONE	0x400	/* wait for tx completion */
 #define CAN_ISOTP_SF_BROADCAST	0x800	/* 1-to-N functional addressing */
 
-/* default values */
+/* protocol machine default values */
 
 #define CAN_ISOTP_DEFAULT_FLAGS		0
 #define CAN_ISOTP_DEFAULT_EXT_ADDRESS	0x00
 #define CAN_ISOTP_DEFAULT_PAD_CONTENT	0xCC /* prevent bit-stuffing */
-#define CAN_ISOTP_DEFAULT_FRAME_TXTIME	0
+#define CAN_ISOTP_DEFAULT_FRAME_TXTIME	50000 /* 50 micro seconds */
 #define CAN_ISOTP_DEFAULT_RECV_BS	0
 #define CAN_ISOTP_DEFAULT_RECV_STMIN	0x00
 #define CAN_ISOTP_DEFAULT_RECV_WFTMAX	0
 
-#define CAN_ISOTP_DEFAULT_LL_MTU	CAN_MTU
-#define CAN_ISOTP_DEFAULT_LL_TX_DL	CAN_MAX_DLEN
-#define CAN_ISOTP_DEFAULT_LL_TX_FLAGS	0
-
 /*
  * Remark on CAN_ISOTP_DEFAULT_RECV_* values:
  *
@@ -162,4 +158,24 @@ struct can_isotp_ll_options {
  * consistency and copied directly into the flow control (FC) frame.
  */
 
+/* link layer default values => make use of Classical CAN frames */
+
+#define CAN_ISOTP_DEFAULT_LL_MTU	CAN_MTU
+#define CAN_ISOTP_DEFAULT_LL_TX_DL	CAN_MAX_DLEN
+#define CAN_ISOTP_DEFAULT_LL_TX_FLAGS	0
+
+/*
+ * The CAN_ISOTP_DEFAULT_FRAME_TXTIME has become a non-zero value as
+ * it only makes sense for isotp implementation tests to run without
+ * a N_As value. As user space applications usually do not set the
+ * frame_txtime element of struct can_isotp_options the new in-kernel
+ * default is very likely overwritten with zero when the sockopt()
+ * CAN_ISOTP_OPTS is invoked.
+ * To make sure that a N_As value of zero is only set intentional the
+ * value '0' is now interpreted as 'do not change the current value'.
+ * When a frame_txtime of zero is required for testing purposes this
+ * CAN_ISOTP_FRAME_TXTIME_ZERO u32 value has to be set in frame_txtime.
+ */
+#define CAN_ISOTP_FRAME_TXTIME_ZERO	0xFFFFFFFF
+
 #endif /* !_UAPI_CAN_ISOTP_H */

isotprecv.c

@@ -57,7 +57,7 @@
 #include <linux/can/isotp.h>
 
 #define NO_CAN_ID 0xFFFFFFFFU
-#define BUFSIZE 5000 /* size > 4095 to check socket API internal checks */
+#define BUFSIZE 67000 /* size > 66000 to check socket API internal checks */
 
 void print_usage(char *prg)
 {

isotpsend.c

@@ -57,7 +57,8 @@
 #include <linux/can/isotp.h>
 
 #define NO_CAN_ID 0xFFFFFFFFU
-#define BUFSIZE 5000 /* size > 4095 to check socket API internal checks */
+#define BUFSIZE 67000 /* size > 66000 kernel buf to test socket API internal checks */
+#define ZERO_STRING "ZERO"
 
 void print_usage(char *prg)
 {
@@ -68,7 +69,7 @@ void print_usage(char *prg)
 	fprintf(stderr, "         -x <addr>[:<rxaddr>]  (extended addressing / opt. separate rxaddr)\n");
 	fprintf(stderr, "         -p [tx]:[rx]  (set and enable tx/rx padding bytes)\n");
 	fprintf(stderr, "         -P <mode>     (check rx padding for (l)ength (c)ontent (a)ll)\n");
-	fprintf(stderr, "         -t <time ns>  (frame transmit time (N_As) in nanosecs)\n");
+	fprintf(stderr, "         -t <time ns>  (frame transmit time (N_As) in nanosecs) (*)\n");
 	fprintf(stderr, "         -f <time ns>  (ignore FC and force local tx stmin value in nanosecs)\n");
 	fprintf(stderr, "         -D <len>      (send a fixed PDU with len bytes - no STDIN data)\n");
 	fprintf(stderr, "         -l <num>      (send num PDUs - use 'i' for infinite loop)\n");
@@ -78,6 +79,7 @@ void print_usage(char *prg)
 	fprintf(stderr, "         -L <mtu>:<tx_dl>:<tx_flags>  (link layer options for CAN FD)\n");
 	fprintf(stderr, "\nCAN IDs and addresses are given and expected in hexadecimal values.\n");
 	fprintf(stderr, "The pdu data is expected on STDIN in space separated ASCII hex values.\n");
+	fprintf(stderr, "(*) = Use '-t %s' to set N_As to zero for Linux version 5.18+\n", ZERO_STRING);
 	fprintf(stderr, "\n");
 }
 
@@ -166,6 +168,9 @@ int main(int argc, char **argv)
 		    break;
 
 	    case 't':
+		    if (!strncmp(optarg, ZERO_STRING, strlen(ZERO_STRING)))
+			    opts.frame_txtime = CAN_ISOTP_FRAME_TXTIME_ZERO;
+		    else
 			    opts.frame_txtime = strtoul(optarg, (char **)NULL, 10);
 		    break;