ubus: fix uc_ubus_have_uloop for eloop+uloop combination

When uloop has been integrated with eloop (in hostapd/wpa_supplicant),
uloop_cancelling will return false, since uloop_run is not being called.
This leads to ubus.defer() calling uloop_run in a context where it can
prevent the other event loop from running.

Fix this by detecting event loop integration via uloop_fd_set_cb being set

Signed-off-by: Felix Fietkau <[email protected]>

CMakeLists.txt

@@ -159,16 +159,21 @@ if(UBUS_SUPPORT)
   set_target_properties(ubus_lib PROPERTIES OUTPUT_NAME ubus PREFIX "")
   target_link_options(ubus_lib PRIVATE ${UCODE_MODULE_LINK_OPTIONS})
   target_link_libraries(ubus_lib ${libubus} ${libblobmsg_json})
+  list(APPEND CMAKE_REQUIRED_LIBRARIES ${libubox})
   file(WRITE "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/test.c" "
     #include <libubus.h>
     int main() { return UBUS_STATUS_NO_MEMORY; }
   ")
   try_compile(HAVE_NEW_UBUS_STATUS_CODES
     ${CMAKE_BINARY_DIR}
     "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/test.c")
+  check_symbol_exists(uloop_fd_set_cb "libubox/uloop.h" FD_SET_CB_EXISTS)
   if(HAVE_NEW_UBUS_STATUS_CODES)
     add_definitions(-DHAVE_NEW_UBUS_STATUS_CODES)
   endif()
+  if(FD_SET_CB_EXISTS)
+    target_compile_definitions(ubus_lib PUBLIC HAVE_ULOOP_FD_SET_CB)
+  endif()
 endif()
 
 if(UCI_SUPPORT)

lib/ubus.c

@@ -665,6 +665,11 @@ uc_ubus_have_uloop(void)
 	bool prev = uloop_cancelled;
 	bool active;
 
+#ifdef HAVE_ULOOP_FD_SET_CB
+	if (uloop_fd_set_cb)
+		return true;
+#endif
+
 	uloop_cancelled = true;
 	active = uloop_cancelling();
 	uloop_cancelled = prev;