Function load_external_function

src/backend/utils/fmgr/dfmgr.c:107–136

* Load the specified dynamic-link library file, and look for a function * named funcname in it. * * If the function is not found, we raise an error if signalNotFound is true, * else return NULL. Note that errors in loading the library * will provoke ereport() regardless of signalNotFound. * * If filehandle is not NULL, then *filehandle will be set to a handle * identifying the library fil

 * at less cost than repeating load_external_function.
 */
void *
load_external_function(const char *filename, const char *funcname,
					   bool signalNotFound, void **filehandle)
{
	char	   *fullname;
	void	   *lib_handle;
	void	   *retval;

	/* Expand the possibly-abbreviated filename to an exact path name */
	fullname = expand_dynamic_library_name(filename);

	/* Load the shared library, unless we already did */
	lib_handle = internal_load_library(fullname);

	/* Return handle if caller wants it */
	if (filehandle)
		*filehandle = lib_handle;

	/* Look up the function within the library. */
	retval = dlsym(lib_handle, funcname);

	if (retval == NULL && signalNotFound)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_FUNCTION),
				 errmsg("could not find function \"%s\" in file \"%s\"",
						funcname, fullname)));

	pfree(fullname);
	return retval;
}

/*
 * This function loads a shlib file without looking up any particular