[SerialImpl]: add function to return pollfd

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

@@ -289,6 +289,18 @@ bool SerialImpl::close()
 	return true;
 }
 
+bool SerialImpl::getPollFd(const px4_pollevent_t events, px4_pollfd_struct_t *pfd)
+{
+	if (!_open) {
+		PX4_ERR("Device not open!");
+		return false;
+	}
+
+	pfd->fd = _serial_fd;
+	pfd->events = events;
+	return true;
+}
+
 ssize_t SerialImpl::bytesAvailable()
 {
 	if (!_open) {

platforms/nuttx/src/px4/common/include/SerialImpl.hpp

@@ -36,6 +36,7 @@
 #include <stdint.h>
 #include <unistd.h>
 
+#include <px4_platform_common/posix.h>
 #include <px4_platform_common/SerialCommon.hpp>
 
 using device::SerialConfig::ByteSize;
@@ -59,6 +60,8 @@ public:
 
 	bool close();
 
+	bool getPollFd(const px4_pollevent_t events, px4_pollfd_struct_t *pfd);
+
 	ssize_t bytesAvailable();
 	ssize_t read(uint8_t *buffer, size_t buffer_size);
 	ssize_t readAtLeast(uint8_t *buffer, size_t buffer_size, size_t character_count = 1, uint32_t timeout_us = 0);