In some cases e.g. with clang on fedora 30 __open2 isn't even declared which results in the following build error: /home/pipo/libvirt/tests/virpcimock.c:939:1: error: no previous prototype for function '__open_2' [-Werror,-Wmissing-prototypes] __open_2(const char *path, int flags) Add a separate declaration to appease the compiler. Signed-off-by: Peter Krempa <pkrempa(a)redhat.com&gt; --- tests/virpcimock.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/tests/virpcimock.c b/tests/virpcimock.c index 829d61cd3f..cfe91ba3ff 100644 --- a/tests/virpcimock.c +++ b/tests/virpcimock.c @@ -935,6 +935,11 @@ open(const char *path, int flags, ...) } +/* in some cases this function may not be present in headers, so we need + * a declaration to silence the complier */ +int +__open_2(const char *path, int flags); + int __open_2(const char *path, int flags) { -- 2.21.0