This patch adds 'get_subflow_info' in 'mptcp_diag', which can check whether
a TCP connection is an MPTCP subflow based on the "INET_ULP_INFO_MPTCP"
with tcp_diag method.

Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 .../testing/selftests/net/mptcp/mptcp_diag.c  | 86 ++++++++++++++++++-
 1 file changed, 84 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c
index 2116b40bc927..28b1704d0c78 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_diag.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c
@@ -8,6 +8,7 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <linux/tcp.h>
+#include <arpa/inet.h>
 
 #include <unistd.h>
 #include <stdlib.h>
@@ -19,8 +20,13 @@
 #define IPPROTO_MPTCP 262
 #endif
 
+#define parse_rtattr_nested(tb, max, rta) \
+	(parse_rtattr_flags((tb), (max), RTA_DATA(rta), RTA_PAYLOAD(rta), \
+			    NLA_F_NESTED))
+
 struct params {
 	__u32 target_token;
+	char subflow_addr[1024];
 };
 
 struct mptcp_info {
@@ -50,6 +56,24 @@ struct mptcp_info {
 	__u32	mptcpi_last_ack_recv;
 };
 
+enum {
+	MPTCP_SUBFLOW_ATTR_UNSPEC,
+	MPTCP_SUBFLOW_ATTR_TOKEN_REM,
+	MPTCP_SUBFLOW_ATTR_TOKEN_LOC,
+	MPTCP_SUBFLOW_ATTR_RELWRITE_SEQ,
+	MPTCP_SUBFLOW_ATTR_MAP_SEQ,
+	MPTCP_SUBFLOW_ATTR_MAP_SFSEQ,
+	MPTCP_SUBFLOW_ATTR_SSN_OFFSET,
+	MPTCP_SUBFLOW_ATTR_MAP_DATALEN,
+	MPTCP_SUBFLOW_ATTR_FLAGS,
+	MPTCP_SUBFLOW_ATTR_ID_REM,
+	MPTCP_SUBFLOW_ATTR_ID_LOC,
+	MPTCP_SUBFLOW_ATTR_PAD,
+
+	__MPTCP_SUBFLOW_ATTR_MAX
+};
+#define MPTCP_SUBFLOW_ATTR_MAX (__MPTCP_SUBFLOW_ATTR_MAX - 1)
+
 static void die_perror(const char *msg)
 {
 	perror(msg);
@@ -58,7 +82,9 @@ static void die_perror(const char *msg)
 
 static void die_usage(int r)
 {
-	fprintf(stderr, "Usage: mptcp_diag -t\n");
+	fprintf(stderr, "Usage:\n"
+			"mptcp_diag -t <token>\n"
+			"mptcp_diag -s \"<saddr> <sport> <daddr> <dport>\"\n");
 	exit(r);
 }
 
@@ -182,6 +208,21 @@ static void parse_nlmsg(struct nlmsghdr *nlh, __u32 proto)
 		}
 		print_info_msg(info);
 	}
+	if (proto == IPPROTO_TCP && tb[INET_DIAG_ULP_INFO]) {
+		struct rtattr *ulpinfo[INET_ULP_INFO_MAX + 1] = { 0 };
+
+		parse_rtattr_nested(ulpinfo, INET_ULP_INFO_MAX,
+				    tb[INET_DIAG_ULP_INFO]);
+
+		if (ulpinfo[INET_ULP_INFO_MPTCP]) {
+			struct rtattr *sfinfo[MPTCP_SUBFLOW_ATTR_MAX + 1] = { 0 };
+
+			parse_rtattr_nested(sfinfo, MPTCP_SUBFLOW_ATTR_MAX,
+					    ulpinfo[INET_ULP_INFO_MPTCP]);
+		} else {
+			printf("It's a normal TCP!\n");
+		}
+	}
 }
 
 static void recv_nlmsg(int fd, __u32 proto)
@@ -244,6 +285,41 @@ static void get_mptcpinfo(__u32 token)
 	close(fd);
 }
 
+static void get_subflow_info(char *subflow_addr)
+{
+	struct inet_diag_req_v2 r = {
+		.sdiag_family           = AF_INET,
+		.sdiag_protocol         = IPPROTO_TCP,
+	};
+	int sport, dport;
+	char saddr[64];	// Take ipv6 into consideration
+	char daddr[64];
+	int ret;
+	int fd;
+
+	ret = sscanf(subflow_addr, "%s %d %s %d", saddr, &sport, daddr, &dport);
+	if (ret != 4)
+		die_perror("IP PORT Pairs has style problems!");
+
+	printf("%s:%d -> %s:%d\n", saddr, sport, daddr, dport);
+
+	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);
+	if (fd < 0)
+		die_perror("Netlink socket");
+
+	r.id.idiag_cookie[0] = INET_DIAG_NOCOOKIE;
+	r.id.idiag_cookie[1] = INET_DIAG_NOCOOKIE;
+	r.id.idiag_sport = htons(sport);
+	r.id.idiag_dport = htons(dport);
+	r.id.idiag_if = 0;
+
+	inet_pton(AF_INET, saddr, &r.id.idiag_src);
+	inet_pton(AF_INET, daddr, &r.id.idiag_dst);
+	r.idiag_ext |= (1 << (INET_DIAG_INFO - 1));
+	send_query(fd, &r, IPPROTO_TCP);
+	recv_nlmsg(fd, IPPROTO_TCP);
+}
+
 static void parse_opts(int argc, char **argv, struct params *p)
 {
 	int c;
@@ -251,7 +327,7 @@ static void parse_opts(int argc, char **argv, struct params *p)
 	if (argc < 2)
 		die_usage(1);
 
-	while ((c = getopt(argc, argv, "ht:")) != -1) {
+	while ((c = getopt(argc, argv, "ht:s:")) != -1) {
 		switch (c) {
 		case 'h':
 			die_usage(0);
@@ -259,6 +335,9 @@ static void parse_opts(int argc, char **argv, struct params *p)
 		case 't':
 			sscanf(optarg, "%x", &p->target_token);
 			break;
+		case 's':
+			snprintf(p->subflow_addr, strlen(optarg) + 1, "%s", optarg);
+			break;
 		default:
 			die_usage(1);
 			break;
@@ -275,6 +354,9 @@ int main(int argc, char *argv[])
 	if (p.target_token)
 		get_mptcpinfo(p.target_token);
 
+	if (strlen(p.subflow_addr) != 0)
+		get_subflow_info(p.subflow_addr);
+
 	return 0;
 }
 
-- 
2.25.1

Hello,

On 16/04/2025 10:59, Gang Yan wrote:
> This patch adds 'get_subflow_info' in 'mptcp_diag', which can check whether
> a TCP connection is an MPTCP subflow based on the "INET_ULP_INFO_MPTCP"
> with tcp_diag method.
> 
> Co-developed-by: Geliang Tang <geliang@kernel.org>
> Signed-off-by: Geliang Tang <geliang@kernel.org>
> Signed-off-by: Gang Yan <yangang@kylinos.cn>
> ---
>  .../testing/selftests/net/mptcp/mptcp_diag.c  | 86 ++++++++++++++++++-
>  1 file changed, 84 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c
> index 2116b40bc927..28b1704d0c78 100644
> --- a/tools/testing/selftests/net/mptcp/mptcp_diag.c
> +++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c
> @@ -8,6 +8,7 @@
>  #include <sys/socket.h>
>  #include <netinet/in.h>
>  #include <linux/tcp.h>
> +#include <arpa/inet.h>
>  
>  #include <unistd.h>
>  #include <stdlib.h>
> @@ -19,8 +20,13 @@
>  #define IPPROTO_MPTCP 262
>  #endif
>  
> +#define parse_rtattr_nested(tb, max, rta) \
> +	(parse_rtattr_flags((tb), (max), RTA_DATA(rta), RTA_PAYLOAD(rta), \
> +			    NLA_F_NESTED))
> +
>  struct params {
>  	__u32 target_token;
> +	char subflow_addr[1024];

detail: maybe add a 's': subflow_addrs.

>  };
>  
>  struct mptcp_info {

(...)

> @@ -244,6 +285,41 @@ static void get_mptcpinfo(__u32 token)
>  	close(fd);
>  }
>  
> +static void get_subflow_info(char *subflow_addr)
> +{
> +	struct inet_diag_req_v2 r = {
> +		.sdiag_family           = AF_INET,
> +		.sdiag_protocol         = IPPROTO_TCP,
> +	};
> +	int sport, dport;
> +	char saddr[64];	// Take ipv6 into consideration

Detail: the comments are usually with the "/* ... */" style. You can
also remove the comment and declare both [sd]addr on the same line I think.

> +	char daddr[64];
> +	int ret;
> +	int fd;
> +
> +	ret = sscanf(subflow_addr, "%s %d %s %d", saddr, &sport, daddr, &dport);
> +	if (ret != 4)
> +		die_perror("IP PORT Pairs has style problems!");
> +
> +	printf("%s:%d -> %s:%d\n", saddr, sport, daddr, dport);
> +
> +	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);
> +	if (fd < 0)
> +		die_perror("Netlink socket");
> +
> +	r.id.idiag_cookie[0] = INET_DIAG_NOCOOKIE;
> +	r.id.idiag_cookie[1] = INET_DIAG_NOCOOKIE;

Can you not set it above, when declaring 'r'? Same for 'idiag_ext'.

> +	r.id.idiag_sport = htons(sport);
> +	r.id.idiag_dport = htons(dport);
> +	r.id.idiag_if = 0;

Do you need to explicitly set it to 0? Is it not 0 by default?

> +
> +	inet_pton(AF_INET, saddr, &r.id.idiag_src);
> +	inet_pton(AF_INET, daddr, &r.id.idiag_dst);
> +	r.idiag_ext |= (1 << (INET_DIAG_INFO - 1));
> +	send_query(fd, &r, IPPROTO_TCP);
> +	recv_nlmsg(fd, IPPROTO_TCP);
> +}
> +
>  static void parse_opts(int argc, char **argv, struct params *p)
>  {
>  	int c;

(...)

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