parlib: Add option file parsing helper

This does the line-by-line work for reading a file: stripping the spaces
and comments.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

user/parlib/include/parlib/opts.h

diff --git a/user/parlib/include/parlib/opts.h b/user/parlib/include/parlib/opts.h
new file mode 100644
index 0000000..a4038c8
--- /dev/null
+++ b/user/parlib/include/parlib/opts.h
@@ -0,0 +1,12 @@
+/* Copyright (c) 2016 Google Inc
+ * Barret Rhoden <brho@cs.berkeley.edu>
+ * See LICENSE for details.
+ *
+ * Various option parsing utility functions. */
+
+#pragma once
+
+/* Parses an option file, calling parse() on individual lines.  We trim the
+ * lines of any leading or trailing spaces first, and ignore anything after #.
+ */
+int parse_opts_file(char *opts_file, void (*parse)(char *));

user/parlib/opts.c

diff --git a/user/parlib/opts.c b/user/parlib/opts.c
new file mode 100644
index 0000000..2c97a17
--- /dev/null
+++ b/user/parlib/opts.c
@@ -0,0 +1,63 @@
+/* Copyright (c) 2016 Google Inc
+ * Barret Rhoden <brho@cs.berkeley.edu>
+ * See LICENSE for details.
+ *
+ * Various option parsing utility functions. */
+
+#include <parlib/opts.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+/* Parses an option file, calling parse() on individual lines.  We trim the
+ * lines of any leading or trailing spaces first, and ignore anything after #.
+ */
+int parse_opts_file(char *opts_file, void (*parse)(char *))
+{
+	char *line = NULL;
+	size_t len = 0;
+	ssize_t read;
+	FILE *fp;
+	char *_line;
+
+	if (!opts_file)
+		return 0;
+	fp = fopen(opts_file, "r");
+	if (!fp)
+		return -1;
+	while ((read = getline(&line, &len, fp)) != -1) {
+		_line = line;
+		/* Drop comments */
+		for (int i = 0; i < read; i++) {
+			if (_line[i] == '#') {
+				_line[i] = 0;
+				read = i;
+				break;
+			}
+		}
+		if (!read)
+			continue;
+		/* Drop trailing spaces */
+		for (int i = read - 1; i >= 0; i--) {
+			if (isspace(_line[i]))
+				_line[i] = 0;
+			else
+				break;
+		}
+		while (isspace(_line[read - 1])) {
+			_line[read - 1] = 0;
+			read--;
+			if (!read)
+				continue;
+		}
+		/* Drop leading spaces */
+		while (isspace(_line[0]))
+			_line++;
+		parse(_line);
+	}
+	free(line);
+	fclose(fp);
+	return 0;
+}