[PATCH mptcp-next v14 09/12] selftests: mptcp: sockopt: use recvmsg instead of read

From: Geliang Tang <[email protected]>

Replace read() with recvmsg() in process_one_client() to enable control
message (CMSG) handling. The original read(fd, buf, sizeof(buf)) is split
into two recvmsg() calls: the first reads exactly one byte, and the second
reads the remaining bytes. This allows the code to access CMSG data for
each received segment, facilitating the upcoming TCP_INQ validation.

Introduce inq_msg_init() and inq_msg_reset() helpers to manage the
struct inq_msg control buffer and iovec, enabling reuse of the same
msghdr across multiple recvmsg() calls with different payload buffers.

Signed-off-by: Geliang Tang <[email protected]>
---
 .../selftests/net/mptcp/mptcp_sockopt.c       | 48 +++++++++++++++++--
 1 file changed, 43 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
index e404aecc7115..080f9d9e34d5 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
@@ -698,36 +698,74 @@ static void check_stat_equal(const char *name, uint64_t actual,
 	       name, actual, expected, (int64_t)(actual - expected));
 }
 
+struct inq_msg {
+	char buf[4096];
+	union {
+		struct cmsghdr cmsg;
+		char msg_buf[4096];
+	} control;
+	struct iovec iov;
+	struct msghdr hdr;
+};
+
+static void inq_msg_init(struct inq_msg *m, size_t iov_len)
+{
+	memset(m, 0, sizeof(*m));
+	m->iov.iov_base = m->buf;
+	m->iov.iov_len = iov_len;
+	m->hdr.msg_iov = &m->iov;
+	m->hdr.msg_iovlen = 1;
+	m->hdr.msg_control = m->control.msg_buf;
+	m->hdr.msg_controllen = sizeof(m->control.msg_buf);
+}
+
+static void inq_msg_reset(struct inq_msg *m, size_t iov_len, void *base)
+{
+	m->iov.iov_base = base;
+	m->iov.iov_len = iov_len;
+	m->hdr.msg_controllen = sizeof(m->control.msg_buf);
+}
+
 static void process_one_client(int fd, int unixfd)
 {
 	struct so_state s;
-	char buf[4096];
+	struct inq_msg m;
 	ssize_t ret;
 	size_t r, w;
 
+	inq_msg_init(&m, 1);
+
 	memset(&s, 0, sizeof(s));
 	do_getsockopts(&s, fd, 0, 0);
 
 	ret = write(unixfd, "xmit", 4);
 	assert(ret == 4);
 
-	ret = read(fd, buf, sizeof(buf));
+	/* read one byte */
+	ret = recvmsg(fd, &m.hdr, 0);
 	if (ret < 0)
-		die_perror("read");
+		die_perror("recvmsg");
 	r = ret;
 
+	inq_msg_reset(&m, sizeof(m.buf) - 1, m.buf + 1);
+	ret = recvmsg(fd, &m.hdr, 0);
+	if (ret < 0)
+		die_perror("recvmsg");
+	r += ret;
+
 	assert(s.mptcpi_rcv_delta <= (uint64_t)r);
 
 	if (s.tcpi_rcv_delta)
 		assert(s.tcpi_rcv_delta == (uint64_t)r);
 
-	ret = write(fd, buf, r);
+	ret = write(fd, m.buf, r);
 	if (ret < 0)
 		die_perror("write");
 	w = ret;
 
 	/* wait for hangup */
-	ret = read(fd, buf, 1);
+	inq_msg_reset(&m, 1, m.buf);
+	ret = recvmsg(fd, &m.hdr, 0);
 	if (ret != 0)
 		xerror("expected EOF, got %zd", ret);
 	r += ret;
-- 
2.53.0