lib:changes for making snmp socket non-blocking

sudhanshukumar22 · sudhanshukumar22 · commit 30f5e1c2eb28 · 2019-09-27T05:18:03.000-07:00
Description: The changes have been done to make the snmp socket non-blocking before calling snmp_read() Problem Description/Summary : vtysh hangs on first try to enter after a reboot with BGP dynamic peers Expected Behavior : VTYSH should not hang When we debug more into bgpd docker by doing gdb on its threads, we find the below thread of bgpd, which is causing the issue. Thread 1 (Thread 0x7f1e1ec46d40 (LWP 47)): (gdb) bt The fix has been taken from the following link. https://sourceforge.net/p/net-snmp/patches/1348/ Signed-off-by: Preetham Singh (preetham.singh@broadcom.com)
diff --git a/lib/agentx.c b/lib/agentx.c
@@ -55,13 +55,32 @@ static int agentx_timeout(struct thread *t)
 static int agentx_read(struct thread *t)
 {
 	fd_set fds;
+	int flags;
+	int nonblock = false;
 	struct listnode *ln = THREAD_ARG(t);
 	list_delete_node(events, ln);
 
+	/* fix for non blocking socket */
+	flags = fcntl(THREAD_FD(t), F_GETFL, 0);
+	if (-1 == flags) {
+		return -1;
+	}
+
+	if (flags & O_NONBLOCK) {
+		nonblock = true;
+	} else {
+		fcntl(THREAD_FD(t), F_SETFL, flags | O_NONBLOCK);
+	}
+
 	FD_ZERO(&fds);
 	FD_SET(THREAD_FD(t), &fds);
 	snmp_read(&fds);
 
+	/* Reset the flag */
+	if (!nonblock){
+		fcntl(THREAD_FD(t), F_SETFL, flags);
+	}
+
 	netsnmp_check_outstanding_agent_requests();
 	agentx_events_update();
 	return 0;
