fixup! Rework maxfd/open_max to avoid unused variables

lib/maxfd.c

@@ -0,0 +1,26 @@
+#include "./maxfd.h"
+#include <errno.h>
+
+long open_max (void) {
+	long maxfd = 0L;
+	/* Try sysconf(_SC_OPEN_MAX) first, as it can be higher than OPEN_MAX.
+	 * If that fails and the macro isn't defined, we fall back to an educated
+	 * guess. There's no guarantee that our guess is adequate and the program
+	 * will die with SIGSEGV if it isn't and the upper boundary is breached. */
+
+#ifdef _SC_OPEN_MAX
+	errno = 0;
+	if ((maxfd = sysconf (_SC_OPEN_MAX)) < 0) {
+		if (errno == 0)
+			maxfd = DEFAULT_MAXFD;   /* it's indeterminate */
+		else
+			die (STATE_UNKNOWN, _("sysconf error for _SC_OPEN_MAX\n"));
+	}
+#elif defined(OPEN_MAX)
+	return OPEN_MAX
+#else	/* sysconf macro unavailable, so guess (may be wildly inaccurate) */
+	return DEFAULT_MAXFD;
+#endif
+
+	return(maxfd);
+}

lib/maxfd.h

@@ -0,0 +1,9 @@
+#ifndef _MAXFD_
+#define _MAXFD_
+
+#define DEFAULT_MAXFD  256   /* fallback value if no max open files value is set */
+#define MAXFD_LIMIT   8192   /* upper limit of open files */
+
+long open_max (void);
+
+#endif // _MAXFD_