Workaround for _PATH_UTMP and _PATH_WTMP defines on musl libc

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/utmp-api.h

@@ -24,6 +24,24 @@
 #ifndef FINIT_UTMP_API_H_
 #define FINIT_UTMP_API_H_
 
+#include <utmp.h>
+
+/*
+ * musl libc default to /dev/null/utmp and /dev/null/wtmp, respectively.
+ * See https://www.openwall.com/lists/musl/2012/03/04/4 for reasoning.
+ *
+ * Also, there's no __MUSL__, so we cannot make a libc-specific check
+ * here to work around this, that's why everyone pays.
+ */
+#undef _PATH_UTMP
+#undef _PATH_WTMP
+#undef _PATH_BTMP
+
+#define _PATH_UTMP "/var/run/wtmp"
+#define _PATH_WTMP "/var/log/wtmp"
+#define _PATH_BTMP "/var/log/btmp"
+
+
 int utmp_set         (int type, int pid, char *line, char *id, char *user);
 int utmp_set_boot    (void);
 int utmp_set_halt    (void);