[PATCH v6 08/12] net/tcp: simplify tcp header filling code

[Mikhail Kshevetskiy]

This patch:
 * remove useless code,
 * use a special function for pretty printing of tcp flags,
 * simplify the code

The behavior should not be changed.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy at iopsys.eu>
---
 net/tcp.c | 74 ++++++++++++++++++++++++++++++-------------------------
 1 file changed, 41 insertions(+), 33 deletions(-)

diff --git a/net/tcp.c b/net/tcp.c
index 37dda6f84f9..0778c153aca 100644
--- a/net/tcp.c
+++ b/net/tcp.c
@@ -535,10 +535,41 @@ void net_set_syn_options(struct tcp_stream *tcp, union tcp_build_pkt *b)
 	b->ip.end = TCP_O_END;
 }
 
+const char *tcpflags_to_str(char tcpflags, char *buf, int size)
+{
+	int i, len;
+	char *orig = buf;
+	const struct {
+		int		bit;
+		const char	*name;
+	} desc[] = {{TCP_RST, "RST"}, {TCP_SYN, "SYN"}, {TCP_PUSH, "PSH"},
+		    {TCP_FIN, "FIN"}, {TCP_ACK, "ACK"}, {0, NULL}};
+
+	*orig = '\0';
+	for (i = 0; desc[i].name; i++) {
+		if (!(tcpflags & desc[i].bit))
+			continue;
+
+		len = strlen(desc[i].name);
+		if (size <= len + 1)
+			break;
+		if (buf != orig) {
+			*buf++ = ',';
+			size--;
+		}
+
+		strcpy(buf, desc[i].name);
+		buf += len;
+		size -= len;
+	}
+	return orig;
+}
+
 int tcp_set_tcp_header(struct tcp_stream *tcp, uchar *pkt, int payload_len,
 		       u8 action, u32 tcp_seq_num, u32 tcp_ack_num)
 {
 	union tcp_build_pkt *b = (union tcp_build_pkt *)pkt;
+	char buf[24];
 	int pkt_hdr_len;
 	int pkt_len;
 	int tcp_len;
@@ -548,55 +579,32 @@ int tcp_set_tcp_header(struct tcp_stream *tcp, uchar *pkt, int payload_len,
 	 *         4 bits reserved options
 	 */
 	b->ip.hdr.tcp_flags = action;
-	pkt_hdr_len = IP_TCP_HDR_SIZE;
 	b->ip.hdr.tcp_hlen = SHIFT_TO_TCPHDRLEN_FIELD(LEN_B_TO_DW(TCP_HDR_SIZE));
 
 	switch (action) {
 	case TCP_SYN:
 		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:SYN (%pI4, %pI4, sq=%u, ak=%u)\n",
-			   &tcp->rhost, &net_ip,
-			   tcp_seq_num, tcp_ack_num);
+			   "TCP Hdr:%s (%pI4, %pI4, s=%u, a=%u)\n",
+			   tcpflags_to_str(action, buf, sizeof(buf)),
+			   &tcp->rhost, &net_ip, tcp_seq_num, tcp_ack_num);
 		net_set_syn_options(tcp, b);
 		pkt_hdr_len = IP_TCP_O_SIZE;
 		break;
-	case TCP_SYN | TCP_ACK:
-	case TCP_ACK:
-		pkt_hdr_len = IP_HDR_SIZE + net_set_ack_options(tcp, b);
-		b->ip.hdr.tcp_flags = action;
-		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:ACK (%pI4, %pI4, s=%u, a=%u, A=%x)\n",
-			   &tcp->rhost, &net_ip, tcp_seq_num, tcp_ack_num,
-			   action);
-		break;
-	case TCP_FIN:
-		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:FIN  (%pI4, %pI4, s=%u, a=%u)\n",
-			   &tcp->rhost, &net_ip, tcp_seq_num, tcp_ack_num);
-		payload_len = 0;
-		pkt_hdr_len = IP_TCP_HDR_SIZE;
-		break;
 	case TCP_RST | TCP_ACK:
 	case TCP_RST:
 		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:RST  (%pI4, %pI4, s=%u, a=%u)\n",
+			   "TCP Hdr:%s (%pI4, %pI4, s=%u, a=%u)\n",
+			   tcpflags_to_str(action, buf, sizeof(buf)),
 			   &tcp->rhost, &net_ip, tcp_seq_num, tcp_ack_num);
+		pkt_hdr_len = IP_TCP_HDR_SIZE;
 		break;
-	/* Notify connection closing */
-	case (TCP_FIN | TCP_ACK):
-	case (TCP_FIN | TCP_ACK | TCP_PUSH):
-		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:FIN ACK PSH(%pI4, %pI4, s=%u, a=%u, A=%x)\n",
-			   &tcp->rhost, &net_ip,
-			   tcp_seq_num, tcp_ack_num, action);
-		fallthrough;
 	default:
 		pkt_hdr_len = IP_HDR_SIZE + net_set_ack_options(tcp, b);
-		b->ip.hdr.tcp_flags = action | TCP_PUSH | TCP_ACK;
 		debug_cond(DEBUG_DEV_PKT,
-			   "TCP Hdr:dft  (%pI4, %pI4, s=%u, a=%u, A=%x)\n",
-			   &tcp->rhost, &net_ip,
-			   tcp_seq_num, tcp_ack_num, action);
+			   "TCP Hdr:%s (%pI4, %pI4, s=%u, a=%u)\n",
+			   tcpflags_to_str(action, buf, sizeof(buf)),
+			   &tcp->rhost, &net_ip, tcp_seq_num, tcp_ack_num);
+		break;
 	}
 
 	pkt_len	= pkt_hdr_len + payload_len;
-- 
2.45.2