Function XPLMFindPluginByPath 

pub unsafe extern "C" fn XPLMFindPluginByPath(
    inPath: *const c_char,
) -> XPLMPluginID

XPLMFindPluginByPath

This routine returns the plug-in ID of the plug-in whose file exists at the passed in absolute file system path. XPLM_NO_PLUGIN_ID is returned if the path does not point to a currently loaded plug-in.