cdev: Fix deallocating devname in nuttx protected/kernel builds

The CDevs always live in kernel side. In kernel the devname
is allocated in kernel heap. Replace "free" with kmm_free on nuttx to
correct the deallocation; this automatically maps to "free" on flat build.

Define __KERNEL__ flag so that the proper nuttx headers are used for building.

TODO: It is fishy in the first place that the devname is allocated in inherited
classes but deleted in the CDev base class. Especially when the devname is
often passed as a constant string (which cannot even be freed) by many drivers.

The allocation and deallocation of devname should be done within the CDev base class
instead.

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

src/lib/cdev/CDev.cpp

@@ -43,6 +43,10 @@
 
 #include <px4_platform_common/posix.h>
 
+#if defined(__PX4_NUTTX)
+#include <nuttx/mm/mm.h>
+#endif
+
 namespace cdev
 {
 
@@ -386,7 +390,11 @@ int CDev::unregister_driver_and_memory()
 	}
 
 	if (_devname != nullptr) {
+#if defined(__PX4_NUTTX) && !defined(CONFIG_BUILD_FLAT)
+		kmm_free((void *)_devname);
+#else
 		free((void *)_devname);
+#endif
 		_devname = nullptr;
 
 	} else {

src/lib/cdev/CMakeLists.txt

@@ -49,7 +49,7 @@ px4_add_library(cdev
 	CDev.hpp
 	${SRCS_PLATFORM}
 )
-target_compile_options(cdev PRIVATE ${MAX_CUSTOM_OPT_LEVEL})
+target_compile_options(cdev PRIVATE ${MAX_CUSTOM_OPT_LEVEL} -D__KERNEL__)
 
 if(PX4_TESTING)
 	add_subdirectory(test)