Additions to the Serial UART API (#22953)

- Added an empty constructor, setPort, and validatePort functions for Serial API
- Changed GPS to not allocate Serial object dynamically
- Moved access check on serial port name into the Serial API
- Improved the Qurt platform validatePort Serial function to implement a more rigorous check. Added safety check
to the setPort Serial function to make sure it isn't called after the port has been already opened.

platforms/posix/include/SerialImpl.hpp

@@ -65,6 +65,8 @@ public:
 	ssize_t write(const void *buffer, size_t buffer_size);
 
 	const char *getPort() const;
+	static bool validatePort(const char *port);
+	bool setPort(const char *port);
 
 	uint32_t getBaudrate() const;
 	bool setBaudrate(uint32_t baudrate);

platforms/posix/src/px4/common/SerialImpl.cpp

@@ -51,9 +51,8 @@ SerialImpl::SerialImpl(const char *port, uint32_t baudrate, ByteSize bytesize, P
 	_stopbits(stopbits),
 	_flowcontrol(flowcontrol)
 {
-	if (port) {
-		strncpy(_port, port, sizeof(_port) - 1);
-		_port[sizeof(_port) - 1] = '\0';
+	if (validatePort(port)) {
+		setPort(port);
 
 	} else {
 		_port[0] = 0;
@@ -190,6 +189,11 @@ bool SerialImpl::open()
 		return true;
 	}
 
+	if (!validatePort(_port)) {
+		PX4_ERR("Invalid port %s", _port);
+		return false;
+	}
+
 	// Open the serial port
 	int serial_fd = ::open(_port, O_RDWR | O_NOCTTY);
 
@@ -317,6 +321,27 @@ const char *SerialImpl::getPort() const
 	return _port;
 }
 
+bool SerialImpl::validatePort(const char *port)
+{
+	return (port && (access(port, R_OK | W_OK) == 0));
+}
+
+bool SerialImpl::setPort(const char *port)
+{
+	if (_open) {
+		PX4_ERR("Cannot set port after port has already been opened");
+		return false;
+	}
+
+	if (validatePort(port)) {
+		strncpy(_port, port, sizeof(_port) - 1);
+		_port[sizeof(_port) - 1] = '\0';
+		return true;
+	}
+
+	return false;
+}
+
 uint32_t SerialImpl::getBaudrate() const
 {
 	return _baudrate;