selftests: openat2: Print also errno in failure messages

In E_func() macro, on error, print also errno in order to aid debugging.

Cc: Aleksa Sarai <[e-mail]>
Signed-off-by: Cristian Marussi <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/openat2/helpers.h

···
 					(similar to chroot(2)). */
 #endif /* RESOLVE_IN_ROOT */
 
-#define E_func(func, ...)						\
-	do {								\
-		if (func(__VA_ARGS__) < 0)				\
-			ksft_exit_fail_msg("%s:%d %s failed\n", \
-					   __FILE__, __LINE__, #func);\
+#define E_func(func, ...)						      \
+	do {								      \
+		errno = 0;						      \
+		if (func(__VA_ARGS__) < 0)				      \
+			ksft_exit_fail_msg("%s:%d %s failed - errno:%d\n",    \
+					   __FILE__, __LINE__, #func, errno); \
 	} while (0)
 
 #define E_asprintf(...)		E_func(asprintf,	__VA_ARGS__)