try to make Utility.Mounts portable

This is an unholy mashup, but it just might work. It works on Linux,
that's all I've tested. :)

Utility/libmounts.c

@@ -0,0 +1,105 @@
+/* mounted filesystems, C mini-library
+ *
+ * Copyright (c) 1980, 1989, 1993, 1994
+ *      The Regents of the University of California.  All rights reserved.
+ * Copyright (c) 2001
+ *      David Rufino <daverufino@btinternet.com>
+ * Copyright 2012
+ *      Joey Hess <joey@kitenet.net>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "libmounts.h"
+
+#include <errno.h>
+#include <stdio.h>
+
+#ifdef GETMNTENT
+/* direct passthrough the getmntent */
+FILE *mounts_start (void) {
+	return setmntent("/etc/mtab", "r");
+}
+int mounts_end (FILE *fp) {
+	return endmntent(fp);
+}
+struct mntent *mounts_next (FILE *fp) {
+	return getmntent(fp);
+}
+#endif
+
+#ifdef GETMNTINFOCALL
+/* getmntent emulation using getmntinfo */
+FILE *mounts_start (void) {
+	return ((FILE *)0x1) /* dummy non-NULL FILE pointer, not used */
+}
+int mounts_end (FILE *fp) {
+	return 1;
+}
+
+static struct mntent _mntent;
+
+static struct mntent *statfs_to_mntent (struct MNTINFOSTRUCT *mntbuf) {
+	_mntent.mnt_fsname = mntbuf->f_mntfromname;
+	_mntent.mnt_dir = mntbuf->f_mntonname;
+	_mntent.mnt_type = mntbuf->f_fstypename;
+
+	_mntent.mnt_opts = '\0';
+	_mntent.mnt_freq = 0;
+	_mntent.mnt_passno = 0;
+
+	return (&_mntent);
+}
+
+static int pos = -1;
+static int mntsize = -1;
+
+struct mntent *mounts_next (FILE *fp) {
+	struct MNTINFOSTRUCT *mntbuf;
+
+	if (pos == -1 || mntsize == -1)
+		mntsize = GETMNTINFOCALL(&mntbuf, MNT_NOWAIT);
+	++pos;
+	if (pos == mntsize) {
+		pos = mntsize = -1;
+		return NULL;
+	}
+
+	return (statfs_to_mntent(&mntbuf[pos]));
+}
+#endif
+
+#ifdef UNKNOWN
+/* dummy, do-nothing version */
+FILE *mounts_start (void) {
+	return ((FILE *)0x1);
+}
+int mounts_end (FILE *fp) {
+	return 1;
+}
+struct mntent *mounts_next (FILE *fp) {
+	return NULL;
+}
+#endif