selftests/xsk: Read current MAX_SKB_FRAGS from sysctl knob

Currently, xskxceiver assumes that MAX_SKB_FRAGS value is always 17
which is not true - since the introduction of BIG TCP this can now take
any value between 17 to 45 via CONFIG_MAX_SKB_FRAGS.

Adjust the TOO_MANY_FRAGS test case to read the currently configured
MAX_SKB_FRAGS value by reading it from /proc/sys/net/core/max_skb_frags.
If running system does not provide that sysctl file then let us try
running the test with a default value.

Signed-off-by: Maciej Fijalkowski <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Magnus Karlsson <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: mfijalko

tools/testing/selftests/bpf/xskxceiver.c

@@ -324,6 +324,25 @@ static bool ifobj_zc_avail(struct ifobject *ifobject)
 	return zc_avail;
 }
 
+#define MAX_SKB_FRAGS_PATH "/proc/sys/net/core/max_skb_frags"
+static unsigned int get_max_skb_frags(void)
+{
+	unsigned int max_skb_frags = 0;
+	FILE *file;
+
+	file = fopen(MAX_SKB_FRAGS_PATH, "r");
+	if (!file) {
+		ksft_print_msg("Error opening %s\n", MAX_SKB_FRAGS_PATH);
+		return 0;
+	}
+
+	if (fscanf(file, "%u", &max_skb_frags) != 1)
+		ksft_print_msg("Error reading %s\n", MAX_SKB_FRAGS_PATH);
+
+	fclose(file);
+	return max_skb_frags;
+}
+
 static struct option long_options[] = {
 	{"interface", required_argument, 0, 'i'},
 	{"busy-poll", no_argument, 0, 'b'},
@@ -2244,13 +2263,24 @@ static int testapp_poll_rxq_tmout(struct test_spec *test)
 
 static int testapp_too_many_frags(struct test_spec *test)
 {
-	struct pkt pkts[2 * XSK_DESC__MAX_SKB_FRAGS + 2] = {};
+	struct pkt *pkts;
 	u32 max_frags, i;
+	int ret;
 
-	if (test->mode == TEST_MODE_ZC)
+	if (test->mode == TEST_MODE_ZC) {
 		max_frags = test->ifobj_tx->xdp_zc_max_segs;
-	else
-		max_frags = XSK_DESC__MAX_SKB_FRAGS;
+	} else {
+		max_frags = get_max_skb_frags();
+		if (!max_frags) {
+			ksft_print_msg("Couldn't retrieve MAX_SKB_FRAGS from system, using default (17) value\n");
+			max_frags = 17;
+		}
+		max_frags += 1;
+	}
+
+	pkts = calloc(2 * max_frags + 2, sizeof(struct pkt));
+	if (!pkts)
+		return TEST_FAILURE;
 
 	test->mtu = MAX_ETH_JUMBO_SIZE;
 
@@ -2280,7 +2310,10 @@ static int testapp_too_many_frags(struct test_spec *test)
 	pkts[2 * max_frags + 1].valid = true;
 
 	pkt_stream_generate_custom(test, pkts, 2 * max_frags + 2);
-	return testapp_validate_traffic(test);
+	ret = testapp_validate_traffic(test);
+
+	free(pkts);
+	return ret;
 }
 
 static int xsk_load_xdp_programs(struct ifobject *ifobj)

tools/testing/selftests/bpf/xskxceiver.h

@@ -55,7 +55,6 @@
 #define XSK_UMEM__LARGE_FRAME_SIZE (3 * 1024)
 #define XSK_UMEM__MAX_FRAME_SIZE (4 * 1024)
 #define XSK_DESC__INVALID_OPTION (0xffff)
-#define XSK_DESC__MAX_SKB_FRAGS 18
 #define HUGEPAGE_SIZE (2 * 1024 * 1024)
 #define PKT_DUMP_NB_TO_PRINT 16
 #define RUN_ALL_TESTS UINT_MAX