[PATCH net-next] selftests: txtimestamp: ignore the old skb from ERRQUEUE

[Jason Xing <kerneljasonxing@gmail.com>]

When I was playing with txtimestamp.c to see how kernel behaves,
I saw the following error outputs if I adjusted the loopback mtu to
1500 and then ran './txtimestamp -4 -L 127.0.0.1 -l 30000 -t 100000':

test SND
    USR: 1740877371 s 488712 us (seq=0, len=0)
    SND: 1740877371 s 489519 us (seq=29999, len=1106)  (USR +806 us)
    USR: 1740877371 s 581251 us (seq=0, len=0)
    SND: 1740877371 s 581970 us (seq=59999, len=8346)  (USR +719 us)
    USR: 1740877371 s 673855 us (seq=0, len=0)
    SND: 1740877371 s 674651 us (seq=89999, len=30000)  (USR +795 us)
    USR: 1740877371 s 765715 us (seq=0, len=0)
ERROR: key 89999, expected 119999
ERROR: -12665 us expected between 0 and 100000
    SND: 1740877371 s 753050 us (seq=89999, len=1106)  (USR +-12665 us)
    SND: 1740877371 s 800783 us (seq=119999, len=30000)  (USR +35068 us)
    USR-SND: count=5, avg=4945 us, min=-12665 us, max=35068 us

Actually, the kernel behaved correctly after I did the analysis. The
second skb carrying 1106 payload was generated due to tail loss probe,
leading to the wrong estimation of tskey in this C program.

This patch does:
- Neglect the old tskey skb received from ERRQUEUE.
- Add a new test to count how many valid skbs received to compare with
cfg_num_pkts.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
Willem, I'm not sure if it's worth reviewing this patch to handle this
testcase. After all it's only a selftest. Well, adding a new test might
be helpful. Please feel free to drop/ignore it if you don't like it.
---
 tools/testing/selftests/net/txtimestamp.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/txtimestamp.c b/tools/testing/selftests/net/txtimestamp.c
index dae91eb97d69..c63af798a521 100644
--- a/tools/testing/selftests/net/txtimestamp.c
+++ b/tools/testing/selftests/net/txtimestamp.c
@@ -86,6 +86,7 @@ static struct timespec ts_usr;
 
 static int saved_tskey = -1;
 static int saved_tskey_type = -1;
+static int saved_num_pkts;
 
 struct timing_event {
 	int64_t min;
@@ -131,17 +132,20 @@ static void add_timing_event(struct timing_event *te,
 	te->total += ts_delta;
 }
 
-static void validate_key(int tskey, int tstype)
+static bool validate_key(int tskey, int tstype)
 {
 	int stepsize;
 
+	if (tskey <= saved_tskey)
+		return false;
+
 	/* compare key for each subsequent request
 	 * must only test for one type, the first one requested
 	 */
 	if (saved_tskey == -1 || cfg_use_cmsg_opt_id)
 		saved_tskey_type = tstype;
 	else if (saved_tskey_type != tstype)
-		return;
+		return true;
 
 	stepsize = cfg_proto == SOCK_STREAM ? cfg_payload_len : 1;
 	stepsize = cfg_use_cmsg_opt_id ? 0 : stepsize;
@@ -152,6 +156,7 @@ static void validate_key(int tskey, int tstype)
 	}
 
 	saved_tskey = tskey;
+	return true;
 }
 
 static void validate_timestamp(struct timespec *cur, int min_delay)
@@ -219,7 +224,8 @@ static void print_timestamp(struct scm_timestamping *tss, int tstype,
 {
 	const char *tsname;
 
-	validate_key(tskey, tstype);
+	if (!validate_key(tskey, tstype))
+		return;
 
 	switch (tstype) {
 	case SCM_TSTAMP_SCHED:
@@ -242,6 +248,7 @@ static void print_timestamp(struct scm_timestamping *tss, int tstype,
 		tstype);
 	}
 	__print_timestamp(tsname, &tss->ts[0], tskey, payload_len);
+	saved_num_pkts++;
 }
 
 static void print_timing_event(char *name, struct timing_event *te)
@@ -582,6 +589,7 @@ static void do_test(int family, unsigned int report_opt)
 		       (char *) &sock_opt, sizeof(sock_opt)))
 		error(1, 0, "setsockopt timestamping");
 
+	saved_num_pkts = 0;
 	for (i = 0; i < cfg_num_pkts; i++) {
 		memset(&msg, 0, sizeof(msg));
 		memset(buf, 'a' + i, total_len);
@@ -673,6 +681,12 @@ static void do_test(int family, unsigned int report_opt)
 		while (!recv_errmsg(fd)) {}
 	}
 
+	if (cfg_num_pkts != saved_num_pkts) {
+		fprintf(stderr, "ERROR: num_pkts received %d, expected %d\n",
+				saved_num_pkts, cfg_num_pkts);
+		test_failed = true;
+	}
+
 	print_timing_event("USR-ENQ", &usr_enq);
 	print_timing_event("USR-SND", &usr_snd);
 	print_timing_event("USR-ACK", &usr_ack);
-- 
2.43.5