[PATCH mptcp-next v2] selftests: mptcp: print stats before socket closure

[PATCH mptcp-next v2] selftests: mptcp: print stats before socket closure

[Matthieu Baerts (NGI0)]

In case of poll timeout, it might be too late to print the stats after
the socket closure.

Now, in case of poll timeout, 'ss' and 'nstat' are invoked from
mptcp_connect to print the stats before exiting. This should help
debugging poll timeout issues.

Note: for this "workaround", system() is used for debugging purposes
only. The returned result can then be safely ignored, hence the (void)!
to avoid unused-result warnings.

Also, 'nstat *Tcp*' will print '#kernel' at the top, but that's OK, and
it seems better to avoid using a pipe here.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- use 'ip netns identify' to avoid a warning from AI reviews
- use 'nstat -s *Tcp*' instead of using grep
- add a note about (void)!
- Link to v1: https://patch.msgid.link/20260814-sft-mptcp-stats-b4-close-v1-1-2945a591be7e@kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_connect.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
index ea4cb6c1bd5e..e906abcd5409 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
@@ -210,6 +210,19 @@ static void xgetaddrinfo(const char *node, const char *service,
 	}
 }
 
+static void print_err_stats(void)
+{
+	char cmd[128];
+
+	snprintf(cmd, sizeof(cmd), "ss -Menitam -o '%cport = :%s' >&2",
+		 listen_mode ? 's' : 'd', cfg_port);
+
+	fprintf(stderr, "socket stats before socket closure:\n");
+	(void)!system(cmd);
+	(void)!system("NSTAT_HISTORY='/tmp/$(ip netns identify).nstat' "
+		      "nstat -s '*Tcp*' >&2");
+}
+
 static void set_rcvbuf(int fd, unsigned int size)
 {
 	int err;
@@ -656,6 +669,7 @@ static int copyfd_io_poll(int infd, int peerfd, int outfd,
 			fprintf(stderr, "%s: poll timed out (events: "
 				"POLLIN %u, POLLOUT %u)\n", __func__,
 				fds.events & POLLIN, fds.events & POLLOUT);
+			print_err_stats();
 			return 2;
 		}
 
@@ -1194,6 +1208,7 @@ int main_loop_s(int listensock)
 		return 1;
 	case 0:
 		fprintf(stderr, "%s: timed out\n", __func__);
+		print_err_stats();
 		close(listensock);
 		return 2;
 	}

---
base-commit: d536472a82d18356d323227213acb5603bb9050c
change-id: 20260814-sft-mptcp-stats-b4-close-20964ff6a6ba

Best regards,
--  
Matthieu Baerts (NGI0) <matttbe@kernel.org>

Re: [PATCH mptcp-next v2] selftests: mptcp: print stats before socket closure

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Shell command substitution inside single quotes prevents evaluation in system() call
--

--- Patch [1]: [PATCH mptcp-next v2] selftests: mptcp: print stats before socket closure ---
commit 3f1a40cd885883e270f0fd3544c47bf2dc166581
Author: Matthieu Baerts (NGI0) <matttbe@kernel.org>

selftests: mptcp: print stats before socket closure

In case of a poll timeout, this commit invokes 'ss' and 'nstat' via
system() to print debug stats before exiting mptcp_connect.

Link: https://patch.msgid.link/20260814-sft-mptcp-stats-b4-close-v1-1-2945a591be7e@kernel.org

> diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
> index ea4cb6c1bd5e2..e906abcd54096 100644
> --- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
> +++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
> @@ -210,6 +210,19 @@ static void xgetaddrinfo(const char *node, const char *service,
>  	}
>  }
>  
> +static void print_err_stats(void)
> +{
> +	char cmd[128];
> +
> +	snprintf(cmd, sizeof(cmd), "ss -Menitam -o '%cport = :%s' >&2",
> +		 listen_mode ? 's' : 'd', cfg_port);
> +
> +	fprintf(stderr, "socket stats before socket closure:\n");
> +	(void)!system(cmd);
> +	(void)!system("NSTAT_HISTORY='/tmp/$(ip netns identify).nstat' "
> +		      "nstat -s '*Tcp*' >&2");

[Severity: Medium]
Will this shell command substitution be evaluated properly?

Because the path is enclosed in single quotes, it appears NSTAT_HISTORY
will be set to the literal string '/tmp/$(ip netns identify).nstat' instead
of being evaluated by the shell.

If the shell does not evaluate the command substitution, could this cause
nstat to look for a non-existent history file and print absolute stats
instead of the expected differential stats?

> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260814-sft-mptcp-stats-b4-close-v2-1-b7a8ab3ddae8@kernel.org?part=1