pktgen: Automate flag enumeration for unknown flag handling

When specifying an unknown flag, it will print all available flags.
Currently, these flags are provided as fixed strings, which requires
manual updates when flags change. Replacing it with automated flag
enumeration.
Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Signed-off-by: Benjamin Poirier <bpoirier@nvidia.com>
Link: https://lore.kernel.org/r/20230920125658.46978-1-liangchen.linux@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/pktgen.c

@@ -1318,9 +1318,10 @@ static ssize_t pktgen_if_write(struct file *file,
 		return count;
 	}
 	if (!strcmp(name, "flag")) {
+		bool disable = false;
 		__u32 flag;
 		char f[32];
-		bool disable = false;
+		char *end;
 
 		memset(f, 0, 32);
 		len = strn_len(&user_buffer[i], sizeof(f) - 1);
@@ -1332,28 +1333,33 @@ static ssize_t pktgen_if_write(struct file *file,
 		i += len;
 
 		flag = pktgen_read_flag(f, &disable);
-
 		if (flag) {
 			if (disable)
 				pkt_dev->flags &= ~flag;
 			else
 				pkt_dev->flags |= flag;
-		} else {
-			sprintf(pg_result,
-				"Flag -:%s:- unknown\nAvailable flags, (prepend ! to un-set flag):\n%s",
-				f,
-				"IPSRC_RND, IPDST_RND, UDPSRC_RND, UDPDST_RND, "
-				"MACSRC_RND, MACDST_RND, TXSIZE_RND, IPV6, "
-				"MPLS_RND, VID_RND, SVID_RND, FLOW_SEQ, "
-				"QUEUE_MAP_RND, QUEUE_MAP_CPU, UDPCSUM, "
-				"NO_TIMESTAMP, "
-#ifdef CONFIG_XFRM
-				"IPSEC, "
-#endif
-				"NODE_ALLOC\n");
+
+			sprintf(pg_result, "OK: flags=0x%x", pkt_dev->flags);
 			return count;
 		}
-		sprintf(pg_result, "OK: flags=0x%x", pkt_dev->flags);
+
+		/* Unknown flag */
+		end = pkt_dev->result + sizeof(pkt_dev->result);
+		pg_result += sprintf(pg_result,
+			"Flag -:%s:- unknown\n"
+			"Available flags, (prepend ! to un-set flag):\n", f);
+
+		for (int n = 0; n < NR_PKT_FLAGS && pg_result < end; n++) {
+			if (!IS_ENABLED(CONFIG_XFRM) && n == IPSEC_SHIFT)
+				continue;
+			pg_result += snprintf(pg_result, end - pg_result,
+					      "%s, ", pkt_flag_names[n]);
+		}
+		if (!WARN_ON_ONCE(pg_result >= end)) {
+			/* Remove the comma and whitespace at the end */
+			*(pg_result - 2) = '\0';
+		}
+
 		return count;
 	}
 	if (!strcmp(name, "dst_min") || !strcmp(name, "dst")) {