From: Geliang Tang <tanggeliang@kylinos.cn>

This patch fixes several issues in the error reporting of the MPTCP sockopt
selftest:

1. Add diff calculation: The error messages for counter mismatches now
   include the actual difference ('diff') between the expected and received
   values, making debugging significantly easier.

2. Fix variable usage: The error check for 'mptcpi_bytes_acked' incorrectly
   used 'ret2' (sent bytes) for both the expected value and the difference
   calculation. It now correctly uses 'ret' (received bytes), which is the
   expected value for bytes_acked.

3. Fix off-by-one in diff: The calculation for the 'mptcpi_rcv_delta' diff
   was 's.mptcpi_rcv_delta - ret', which is off-by-one. It has been corrected
   to 's.mptcpi_rcv_delta - (ret + 1)' to match the expected value in the
   condition above it.

Fixes: 5dcff89e1455 ("selftests: mptcp: explicitly tests aggregate counters")
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 .../testing/selftests/net/mptcp/mptcp_sockopt.c  | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
index b616af36c16f..56dfd02c5d01 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
@@ -667,22 +667,26 @@ static void process_one_client(int fd, int pipefd)
 
 	do_getsockopts(&s, fd, ret, ret2);
 	if (s.mptcpi_rcv_delta != (uint64_t)ret + 1)
-		xerror("mptcpi_rcv_delta %" PRIu64 ", expect %" PRIu64, s.mptcpi_rcv_delta, ret + 1, s.mptcpi_rcv_delta - ret);
+		xerror("mptcpi_rcv_delta %" PRIu64 ", expect %" PRIu64 ", diff %" PRId64,
+		       s.mptcpi_rcv_delta, ret + 1, s.mptcpi_rcv_delta - (ret + 1));
 
 	/* be nice when running on top of older kernel */
 	if (s.pkt_stats_avail) {
 		if (s.last_sample.mptcpi_bytes_sent != ret2)
-			xerror("mptcpi_bytes_sent %" PRIu64 ", expect %" PRIu64,
+			xerror("mptcpi_bytes_sent %" PRIu64 ", expect %" PRIu64
+			       ", diff %" PRId64,
 			       s.last_sample.mptcpi_bytes_sent, ret2,
 			       s.last_sample.mptcpi_bytes_sent - ret2);
 		if (s.last_sample.mptcpi_bytes_received != ret)
-			xerror("mptcpi_bytes_received %" PRIu64 ", expect %" PRIu64,
+			xerror("mptcpi_bytes_received %" PRIu64 ", expect %" PRIu64
+			       ", diff %" PRId64,
 			       s.last_sample.mptcpi_bytes_received, ret,
 			       s.last_sample.mptcpi_bytes_received - ret);
 		if (s.last_sample.mptcpi_bytes_acked != ret)
-			xerror("mptcpi_bytes_acked %" PRIu64 ", expect %" PRIu64,
-			       s.last_sample.mptcpi_bytes_acked, ret2,
-			       s.last_sample.mptcpi_bytes_acked - ret2);
+			xerror("mptcpi_bytes_acked %" PRIu64 ", expect %" PRIu64
+			       ", diff %" PRId64,
+			       s.last_sample.mptcpi_bytes_acked, ret,
+			       s.last_sample.mptcpi_bytes_acked - ret);
 	}
 
 	close(pipefd);
-- 
2.48.1

Hi Geliang,

On 03/09/2025 06:08, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> This patch fixes several issues in the error reporting of the MPTCP sockopt
> selftest:
> 
> 1. Add diff calculation: The error messages for counter mismatches now
>    include the actual difference ('diff') between the expected and received
>    values, making debugging significantly easier.

This could be interpreted as a new feature while it is a fix. What about:

  Fix diff not printed: The error messages for counter mismatches had
  the actual difference ('diff') as argument, but it was missing in the
  format string. Displaying it makes the debugging easier.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.