Patch reverts upstream commit: https://github.com/collectd/collectd/commit/6124da7a48f28f54fc09ebeb942d1037516fe6ab The commit changed the detection path due to FreeBSD issues, but apparently affects also Openwrt buildroot negatively. Original explanation: From 6124da7a48f28f54fc09ebeb942d1037516fe6ab Mon Sep 17 00:00:00 2001 Subject: [PATCH] Fix libmodbus detection on FreeBSD We look for modbus/modbus.h in /usr/local/include/modbus but we should look for modbus.h This is only an issue on FreeBSD since /usr/local/include is not in the default search path. Reversed patch to be applied: --- a/configure.ac +++ b/configure.ac @@ -2626,7 +2626,7 @@ then SAVE_CPPFLAGS="$CPPFLAGS" CPPFLAGS="$CPPFLAGS $with_libmodbus_cflags" - AC_CHECK_HEADERS(modbus.h, [], [with_libmodbus="no (modbus.h not found)"]) + AC_CHECK_HEADERS(modbus/modbus.h, [], [with_libmodbus="no (modbus/modbus.h not found)"]) CPPFLAGS="$SAVE_CPPFLAGS" fi --- a/src/modbus.c +++ b/src/modbus.c @@ -27,7 +27,7 @@ #include -#include +#include #ifndef LIBMODBUS_VERSION_CHECK /* Assume version 2.0.3 */