libmount: add support for mtab managment

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 965 insertions, 0 deletions

diff --git a/shlibs/mount/src/mtab.c b/shlibs/mount/src/mtab.c
new file mode 100644
index 000000000..81b01f2be
--- /dev/null
+++ b/shlibs/mount/src/mtab.c
@@ -0,0 +1,965 @@
+/*
+ * Copyright (C) 2010 Karel Zak <kzak@redhat.com>
+ *
+ * This file may be redistributed under the terms of the
+ * GNU Lesser General Public License.
+ */
+
+/**
+ * SECTION: mtab
+ * @title: mtab managment
+ * @short_description: userspace mount information management
+ *
+ * The libmount library allows to use more modes for mtab management:
+ *
+ * - /etc/mtab is regular file
+ *
+ *   then libmount manages the file in classical way (all mounts are
+ *   added to the file)
+ *
+ * - /etc/mtab is symlink
+ *
+ *   then libmount ignores mtab at all
+ *
+ * - /etc/mtab is symlink and /var/run/mount/ directory exists
+ *
+ *   then libmount stores userspace specific mount options to the
+ *   /var/run/mount/mountinfo file (the file format compatible to
+ *   /proc/self/mountinfo)
+ *
+ *
+ * The mtab is always updated in two steps. The first step is to prepare a new
+ * mtab entry -- mnt_mtab_prepare_update(), this step has to be done before
+ * mount(2) syscall. The second step is to update the mtab file --
+ * mnt_update_mtab(), this step should be done after mount(2) syscall.
+ *
+ * The mnt_update_mtab() behaviour is undefined if mnt_mtab_prepare_update() has
+ * not been used.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+#include "c.h"
+#include "mountP.h"
+#include "mangle.h"
+#include "pathnames.h"
+
+
+
+/*
+ * mtab update description
+ */
+struct _mnt_mtab {
+	int		action;		/* MNT_ACT_{MOUNT,UMOUNT} */
+	int		mountflags;	/* MS_* flags */
+	char		*filename;	/* usually /etc/mtab or /var/run/mount/mountinfo */
+	char		*old_target;	/* for MS_MOVE */
+	int		format;		/* MNT_FMT_{MTAB,MOUNTINFO} */
+	int		nolock;		/* don't alloca private mnt_lock */
+	mnt_fs		*fs;		/* entry */
+	mnt_lock	*lc;		/* lock or NULL */
+};
+
+/**
+ * mnt_new_mtab:
+ * @action: MNT_ACT_{MOUNT,UMOUNT}
+ *
+ * Returns: newly allocated mtab description
+ */
+mnt_mtab *mnt_new_mtab(int action)
+{
+	mnt_mtab *mt;
+
+	mt = calloc(1, sizeof(struct _mnt_mtab));
+	if (!mt)
+		return NULL;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: allocate\n", mt));
+
+	mt->action = action;
+	mt->fs = mnt_new_fs();
+	if (!mt->fs)
+		goto err;
+	return mt;
+err:
+	mnt_free_fs(mt->fs);
+	free(mt);
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab: failed to allocate handler\n"));
+
+	return NULL;
+}
+
+/**
+ * mnt_free_mtab:
+ * @mt: mtab
+ *
+ * Deallocates mnt_mtab handler.
+ */
+void mnt_free_mtab(mnt_mtab *mt)
+{
+	if (!mt)
+		return;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: deallacate\n", mt));
+
+	mnt_free_lock(mt->lc);
+	free(mt->filename);
+	free(mt);
+}
+
+/**
+ * mnt_mtab_set_filename:
+ * @mt: mtab
+ * @filename: path to mtab (default is /etc/mtab or /var/run/mount/mountinfo)
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_filename(mnt_mtab *mt, const char *filename)
+{
+	char *p = NULL;
+	assert(mt);
+
+	if (!mt)
+		return -1;
+	if (filename) {
+		p = strdup(filename);
+		if (!p)
+			return -1;
+	}
+	free(mt->filename);
+	mt->filename = p;
+	return 0;
+}
+
+/**
+ * mnt_mtab_set_action:
+ * @mt: mtab
+ * @action: MNT_ACT_{MOUNT,UMOUNT}
+ *
+ * Overwrites the previously defined action by mnt_new_mtab().
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_action(mnt_mtab *mt, int action)
+{
+	assert(mt);
+	if (!mt)
+		return -1;
+	mt->action = action;
+	return 0;
+}
+
+/**
+ * mnt_mtab_set_format:
+ * @mt: mtab
+ * @format: MNT_FMT_{MTAB,MOUNTINFO}
+ *
+ * Sets mtab file format, default is MNT_FMT_MTAB for paths that end with
+ * "mtab" and MNT_FMT_MOUNTINFO for paths that end with "mountinfo".
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_format(mnt_mtab *mt, int format)
+{
+	assert(mt);
+	if (!mt)
+		return -1;
+	mt->format = format;
+	return 0;
+}
+
+/**
+ * mnt_mtab_set_optstr:
+ * @mt: mtab
+ * @optstr: mount options that will be used for mount(2)
+ *
+ * Note that mnt_mtab_prepare_update() will remove options that does not belong
+ * to mtab.
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_optstr(mnt_mtab *mt, const char *optstr)
+{
+	if (!mt)
+		return -1;
+	return mnt_fs_set_optstr(mt->fs, optstr);
+}
+
+/**
+ * mnt_mtab_set_mountflags:
+ * @mt: mtab
+ * @flags: MS_{REMOUNT,MOVE}
+ *
+ * Sets mount flags for mount/umount action. The flags are also
+ * extracted from mount options by mnt_mtab_prepare_update().
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_mountflags(mnt_mtab *mt, int flags)
+{
+	assert(mt);
+	if (!mt)
+		return -1;
+	mt->mountflags = flags;
+	return 0;
+}
+
+/**
+ * mnt_mtab_get_lock:
+ * @mt: mtab
+ *
+ * This function should not be called before mnt_mtab_prepare_update(). The lock
+ * is initialized when mtab update is required only.
+ *
+ * Note that after mnt_mtab_disable_lock(mt, TRUE) or after mnt_free_mtab()
+ * the lock will be automaticaly deallocated.
+ *
+ * Returns: libmount lock handler or NULL if locking is disabled.
+ */
+mnt_lock *mnt_mtab_get_lock(mnt_mtab *mt)
+{
+	return mt ? mt->lc : NULL;
+}
+
+/**
+ * mnt_mtab_disable_lock:
+ * @mt: mtab
+ * @disable: TRUE/FALSE
+ *
+ * Enable or disable mtab locking, the locking is enabled by default.
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_disable_lock(mnt_mtab *mt, int disable)
+{
+	if (!mt)
+		return -1;
+	if (disable) {
+		mnt_free_lock(mt->lc);
+		mt->lc = NULL;
+	}
+	mt->nolock = disable;
+	return 0;
+}
+
+/**
+ * mnt_mtab_set_source:
+ * @mt: mtab
+ * @source: device or directory name
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_source(mnt_mtab *mt, const char *source)
+{
+	return mt ? mnt_fs_set_source(mt->fs, source) : -1;
+}
+
+/**
+ * mnt_mtab_set_target:
+ * @mt: mtab
+ * @target: mountpoint
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_target(mnt_mtab *mt, const char *target)
+{
+	return mt ? mnt_fs_set_target(mt->fs, target) : -1;
+}
+
+/**
+ * mnt_mtab_set_old_target:
+ * @mt: mtab
+ * @target: old mountpoint
+ *
+ * Sets the original target for the MS_MOVE operation.
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_old_target(mnt_mtab *mt, const char *target)
+{
+	if (!mt)
+		return -1;
+	mt->old_target = strdup(target);
+	if (!mt->old_target)
+		return -1;
+	return 0;
+}
+
+/**
+ * mnt_mtab_set_fstype:
+ * @mt: mtab
+ * @fstype: filesystem type (e.g. "ext3")
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_mtab_set_fstype(mnt_mtab *mt, const char *fstype)
+{
+	if (!mt)
+		return -1;
+	return mnt_fs_set_fstype(mt->fs, fstype);
+}
+
+
+/*
+ * The format is same as /proc/self/mountinfo, but it contains userspace
+ * mount options and some unncessary fields are ignored.
+ */
+static int fprintf_mountinfo_fs(FILE *f, mnt_fs *fs)
+{
+	char *root = NULL, *target = NULL, *optstr = NULL,
+	     *fstype = NULL, *source = NULL;
+	int rc = -1;
+	dev_t devno;
+
+	assert(fs);
+	assert(f);
+
+	if (!fs || !f)
+		return -1;
+	devno = mnt_fs_get_devno(fs);
+	source = mangle(mnt_fs_get_source(fs));
+	root = mangle(mnt_fs_get_root(fs));
+	target = mangle(mnt_fs_get_target(fs));
+	fstype = mangle(mnt_fs_get_fstype(fs));
+	optstr = mangle(mnt_fs_get_optstr(fs));
+
+	if (!root || !target || !optstr)
+		goto done;
+
+	rc = fprintf(f, "%i %i %u:%u %s %s %s - %s %s %s\n",
+			mnt_fs_get_id(fs),
+			mnt_fs_get_parent_id(fs),
+			major(devno), minor(devno),
+			root,
+			target,
+			optstr,
+			fstype ? fstype : "auto",
+			source ? source : "none",
+			"none");
+	rc = 0;
+done:
+	free(root);
+	free(target);
+	free(optstr);
+	free(fstype);
+	free(source);
+	return rc;
+}
+
+static int fprintf_mtab_fs(FILE *f, mnt_fs *fs)
+{
+	char *m1 = NULL, *m2 = NULL, *m3 = NULL, *m4 = NULL;
+	int rc = -1;
+
+	assert(fs);
+	assert(f);
+
+	if (!fs || !f)
+		return -1;
+
+	m1 = mangle(mnt_fs_get_source(fs));
+	m2 = mangle(mnt_fs_get_target(fs));
+	m3 = mangle(mnt_fs_get_fstype(fs));
+	m4 = mangle(mnt_fs_get_optstr(fs));
+
+	if (!m1 || !m2 || !m3 || !m4)
+		goto done;
+
+	rc = fprintf(f, "%s %s %s %s %d %d\n",
+				m1, m2, m3, m4,
+				mnt_fs_get_freq(fs),
+				mnt_fs_get_passno(fs));
+	rc = 0;
+done:
+	free(m1);
+	free(m2);
+	free(m3);
+	free(m4);
+
+	return rc;
+}
+
+static int update_file(const char *filename, int fmt, mnt_tab *tb)
+{
+	mnt_iter itr;
+	mnt_fs *fs;
+	FILE *f = NULL;
+	char tmpname[PATH_MAX];
+	struct stat st;
+	int fd;
+	int (*line_fn)(FILE *, mnt_fs *);
+
+	assert(tb);
+	if (!tb)
+		goto error;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %s: update from tab %p\n", filename, tb));
+
+	if (snprintf(tmpname, sizeof(tmpname), "%s.tmp", filename)
+						>= sizeof(tmpname))
+		goto error;
+
+	f = fopen(tmpname, "w");
+	if (!f)
+		goto error;
+
+	line_fn = fmt == MNT_FMT_MTAB ? fprintf_mtab_fs : fprintf_mountinfo_fs;
+
+	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
+	while(mnt_tab_next_fs(tb, &itr, &fs) == 0)
+		line_fn(f, fs);
+
+	fd = fileno(f);
+
+	if (fchmod(fd, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH) < 0)
+		goto error;
+
+	/* Copy uid/gid from the present file before renaming. */
+	if (stat(filename, &st) == 0) {
+		if (fchown(fd, st.st_uid, st.st_gid) < 0)
+			goto error;
+	}
+
+	fclose(f);
+	f = NULL;
+
+	if (rename(tmpname, filename) < 0)
+		goto error;
+
+	return 0;
+error:
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %s: update from tab %p failed\n", filename, tb));
+	if (f)
+		fclose(f);
+	return -1;
+}
+
+static int set_fs_root(mnt_mtab *mt, mnt_fs *fs)
+{
+	char *root = NULL, *mnt = NULL;
+	const char *fstype;
+	char *optstr;
+	mnt_tab *tb = NULL;
+
+	if (mt->mountflags & MS_REMOUNT)
+		return 0;
+
+	optstr = (char *) mnt_fs_get_optstr(fs);
+	fstype = mnt_fs_get_fstype(fs);
+
+	/*
+	 * bind-mount -- get fs-root and source device for the source filesystem
+	 */
+	if (mt->mountflags & MS_BIND) {
+		const char *src, *src_root;
+		mnt_fs *src_fs;
+
+		src = mnt_fs_get_srcpath(fs);
+		if (!src)
+			goto err;
+		mnt = mnt_get_mountpoint(src);
+		if (!mnt)
+			goto err;
+		root = mnt_get_fs_root(src, mnt);
+
+		tb = mnt_new_tab_from_file(_PATH_PROC_MOUNTINFO);
+		if (!tb)
+			goto dflt;
+		src_fs = mnt_tab_find_target(tb, mnt, MNT_ITER_BACKWARD);
+		if (!src_fs)
+			goto dflt;
+
+		/* set device name and fs */
+		src = mnt_fs_get_srcpath(src_fs);
+		mnt_fs_set_source(fs, src);
+
+		mnt_fs_set_fstype(fs, mnt_fs_get_fstype(src_fs));
+
+		/* on btrfs the subvolume is used as fs-root in
+		 * /proc/self/mountinfo, so we have get the original subvolume
+		 * name from src_fs and prepend the subvolume name to the
+		 * fs-root path
+		 */
+		src_root = mnt_fs_get_root(src_fs);
+		if (src_root && !startswith(root, src_root)) {
+			size_t sz = strlen(root) + strlen(src_root) + 1;
+			char *tmp = malloc(sz);
+
+			if (!tmp)
+				goto err;
+			snprintf(tmp, sz, "%s%s", src_root, root);
+			free(root);
+			root = tmp;
+		}
+	}
+
+	/*
+	 * btrfs-subvolume mount -- get subvolume name and use it as a root-fs path
+	 */
+	else if (fstype && !strcmp(fstype, "btrfs")) {
+		char *vol = NULL, *p;
+		size_t sz, volsz = 0;
+
+		if (mnt_optstr_get_option(optstr, "subvol", &vol, &volsz))
+			goto dflt;
+
+		sz = volsz;
+		if (*vol != '/')
+			sz++;
+		root = malloc(sz + 1);
+		if (!root)
+			goto err;
+		p = root;
+		if (*vol != '/')
+			*p++ = '/';
+		memcpy(p, vol, volsz);
+		*(root + sz) = '\0';
+	}
+
+dflt:
+	mnt_free_tab(tb);
+	if (!root)
+		root = strdup("/");
+	if (!root)
+		goto err;
+	fs->root = root;
+	free(mnt);
+	return 0;
+err:
+	free(root);
+	free(mnt);
+	return -1;
+}
+
+/**
+ * mnt_mtab_prepare_update:
+ * @mt: mtab
+ *
+ * Prepares internal data for mtab update:
+ * - set mtab filename if mnt_mtab_set_filename() was't called
+ * - set mtab file format if mnt_mtab_set_format() was't called
+ * - (bitwise) OR mountflags from mount options
+ * - for /var/run/mount/mountinfo:
+ *   * evaluate if mtab update is necessary
+ *   * set fs root and devname for bind mount and btrfs subvolumes
+ * - allocate mtab_lock if necessary
+ *
+ * This function has to be always called before mount(2). The mnt_update_mtab()
+ * should not be called is mnt_mtab_prepare_update() returns non-zero value.
+ *
+ * Returns: 0 on success, 1 if update is unncessary, -1 in case of error
+ */
+int mnt_mtab_prepare_update(mnt_mtab *mt)
+{
+	char *u = NULL;
+	const char *o = NULL;
+
+	assert(mt);
+
+	if (!mt)
+		return -1;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: prepare update (target %s, source %s, optstr %s)\n",
+		mt, mnt_fs_get_target(mt->fs), mnt_fs_get_source(mt->fs),
+		mnt_fs_get_optstr(mt->fs)));
+
+	if (!mt->filename) {
+		const char *p = mnt_get_writable_mtab_path();
+		if (!p) {
+			if (errno)
+			       goto err;	/* EACCES? */
+			goto nothing;		/* no mtab */
+		}
+		mt->filename = strdup(p);
+		if (!mt->filename)
+			goto err;
+	}
+	if (!mt->format)
+		mt->format = endswith(mt->filename, "mountinfo") ?
+					MNT_FMT_MOUNTINFO : MNT_FMT_MTAB;
+
+
+	/* TODO: cannonicalize source and target paths on mnt->fs */
+
+	o = mnt_fs_get_optstr(mt->fs);
+	if (o)
+		mt->mountflags |= mnt_optstr_get_mountflags(o);
+
+	/* umount */
+	if (mt->action == MNT_ACT_UMOUNT)
+		return 0;
+
+	/*
+	 * A) classic /etc/mtab
+	 */
+	if (mt->format != MNT_FMT_MOUNTINFO)
+		return 0;
+
+	/*
+	 * B) /var/run/mount/mountinfo
+	 */
+	if (mt->mountflags & MS_REMOUNT) {
+		/* remount */
+		if (mnt_split_optstr(o, &u, NULL, NULL, MNT_NOMTAB, 0))
+			goto err;
+		if (mnt_fs_set_optstr(mt->fs, u))
+			goto err;
+
+	} else {
+		if (!o)
+			goto nothing;	/* no options */
+		if (mnt_split_optstr(o, &u, NULL, NULL, MNT_NOMTAB, 0))
+			goto err;
+		if (!u)
+			goto nothing;	/* no userpsace options */
+		if (set_fs_root(mt, mt->fs))
+			goto err;
+		mnt_fs_set_optstr(mt->fs, u);
+	}
+
+	if (!mt->nolock && !mt->lc) {
+		mt->lc = mnt_new_lock(mt->filename, 0);
+		if (!mt->lc)
+			goto err;
+	}
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: prepare update: success\n", mt));
+	free(u);
+	return 0;
+err:
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: prepare update: failed\n", mt));
+	free(u);
+	return -1;
+nothing:
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: prepare update: unnecessary\n", mt));
+	free(u);
+	return 1;
+}
+
+static int add_entry(mnt_mtab *mt)
+{
+	FILE *f;
+	int rc = -1;
+
+	assert(mt);
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: add entry\n", mt));
+	if (mt->lc)
+		mnt_lock_file(mt->lc);
+	f = fopen(mt->filename, "a+");
+	if (f) {
+		if (mt->format == MNT_FMT_MOUNTINFO)
+			rc = fprintf_mountinfo_fs(f, mt->fs);
+		else
+			rc = fprintf_mtab_fs(f, mt->fs);
+		fclose(f);
+	}
+	if (mt->lc)
+		mnt_unlock_file(mt->lc);
+	return rc;
+}
+
+static int remove_entry(mnt_mtab *mt)
+{
+	const char *target;
+	mnt_tab *tb = NULL;
+	mnt_fs *fs = NULL;
+	int rc = -1;
+
+	assert(mt);
+	assert(mt->filename);
+
+	target = mnt_fs_get_target(mt->fs);
+	assert(target);
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: remove entry (target %s)\n", mt, target));
+
+	if (mt->lc)
+		mnt_lock_file(mt->lc);
+	tb = mnt_new_tab_from_file(mt->filename);
+	if (!tb)
+		goto done;
+	fs = mnt_tab_find_target(tb, target, MNT_ITER_BACKWARD);
+	if (!fs) {
+		rc = 0;	/* no error if the file does not contain the target */
+		goto done;
+	}
+	mnt_tab_remove_fs(tb, fs);
+
+	if (!update_file(mt->filename, mt->format, tb))
+		rc = 0;
+done:
+	if (mt->lc)
+		mnt_unlock_file(mt->lc);
+	mnt_free_tab(tb);
+	mnt_free_fs(fs);
+	return rc;
+}
+
+static int modify_target(mnt_mtab *mt)
+{
+	mnt_tab *tb = NULL;
+	mnt_fs *fs = NULL;
+	int rc = -1;
+
+	assert(mt);
+	assert(mt->old_target);
+	assert(mt->filename);
+	assert(mnt_fs_get_target(mt->fs));
+
+	if (!mt->old_target)
+		return -1;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: modify target (%s->%s)\n", mt,
+		mt->old_target, mnt_fs_get_target(mt->fs)));
+
+	if (mt->lc)
+		mnt_lock_file(mt->lc);
+	tb = mnt_new_tab_from_file(mt->filename);
+	if (!tb)
+		goto done;
+	fs = mnt_tab_find_target(tb, mt->old_target, MNT_ITER_BACKWARD);
+	if (!fs) {
+		rc = 0;	/* no error if the file does not contain the target */
+		goto done;
+	}
+
+	mnt_fs_set_target(fs, mnt_fs_get_target(mt->fs));
+
+	if (!update_file(mt->filename, mt->format, tb))
+		rc = 0;
+done:
+	if (mt->lc)
+		mnt_unlock_file(mt->lc);
+	mnt_free_tab(tb);
+	return rc;
+}
+
+static int modify_options(mnt_mtab *mt)
+{
+	mnt_tab *tb = NULL;
+	mnt_fs *fs = NULL, *rem_fs = NULL;
+	int rc = -1;
+	const char *target = mnt_fs_get_target(mt->fs);
+
+	assert(target);
+	assert(mt->filename);
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: modify options (target %s)\n", mt, target));
+
+	if (mt->lc)
+		mnt_lock_file(mt->lc);
+	tb = mnt_new_tab_from_file(mt->filename);
+	if (!tb)
+		goto done;
+	fs = mnt_tab_find_target(tb, target, MNT_ITER_BACKWARD);
+	if (!fs) {
+		rc = 0;	/* no error if the file does not contain the target */
+		goto done;
+	}
+	if (mt->format == MNT_FMT_MOUNTINFO && !mnt_fs_get_optstr(mt->fs)) {
+		mnt_tab_remove_fs(tb, fs);
+		rem_fs = fs;
+	} else
+		mnt_fs_set_optstr(fs, mnt_fs_get_optstr(mt->fs));
+
+	if (!update_file(mt->filename, mt->format, tb))
+		rc = 0;
+done:
+	if (mt->lc)
+		mnt_unlock_file(mt->lc);
+	mnt_free_tab(tb);
+	mnt_free_fs(rem_fs);
+	return rc;
+}
+
+/**
+ * mnt_update_mtab:
+ * @mt: mtab
+ *
+ * Updates the mtab file. The behavior of this function is undefined if
+ * mnt_mtab_prepare_update() has not been called.
+ *
+ * Returns: 0 on success, -1 in case of error.
+ */
+int mnt_update_mtab(mnt_mtab *mt)
+{
+	assert(mt);
+	assert(mt->filename);
+	assert(mt->format);
+
+	if (!mt)
+		return -1;
+
+	DBG(DEBUG_MTAB, fprintf(stderr,
+		"libmount: mtab %p: update (target %s)\n", mt,
+		mnt_fs_get_target(mt->fs)));
+	/*
+	 * umount
+	 */
+	if (mt->action == MNT_ACT_UMOUNT)
+		return remove_entry(mt);
+	/*
+	 * mount
+	 */
+	if (mt->action == MNT_ACT_MOUNT) {
+		if (mt->mountflags & MS_REMOUNT)
+			return modify_options(mt);
+
+		if (mt->mountflags & MS_MOVE)
+			return modify_target(mt);
+
+		return add_entry(mt);	/* mount */
+	}
+	return -1;
+}
+
+#ifdef TEST_PROGRAM
+
+#include <errno.h>
+
+mnt_lock *lock;
+
+static void lock_fallback(void)
+{
+	if (lock)
+		mnt_unlock_file(lock);
+}
+
+static int update(mnt_mtab *mt)
+{
+	int rc;
+
+	/*
+	 * Note that mount(2) syscal should be called *after*
+	 * mnt_mtab_prepare_update() and *before* mnt_update_mtab()
+	 */
+	rc = mnt_mtab_prepare_update(mt);
+	if (!rc) {
+		/* setup lock fallback */
+		lock = mnt_mtab_get_lock(mt);
+		atexit(lock_fallback);
+
+		return mnt_update_mtab(mt);
+	}
+	if (rc == 1) {
+		printf("mtab: update is not reuquired\n");
+		return 0;
+	}
+	fprintf(stderr, "mtab: failed to prepare update\n");
+	return -1;
+}
+
+int test_add(struct mtest *ts, int argc, char *argv[])
+{
+	mnt_mtab *mt;
+	int rc = -1;
+
+	if (argc < 5)
+		return -1;
+	mt = mnt_new_mtab(MNT_ACT_MOUNT);
+	if (!mt)
+		return -1;
+	mnt_mtab_set_source(mt, argv[1]);
+	mnt_mtab_set_target(mt, argv[2]);
+	mnt_mtab_set_fstype(mt, argv[3]);
+	mnt_mtab_set_optstr(mt, argv[4]);
+
+	rc = update(mt);
+
+	mnt_free_mtab(mt);
+	return rc;
+}
+
+int test_remove(struct mtest *ts, int argc, char *argv[])
+{
+	mnt_mtab *mt;
+	int rc = -1;
+
+	if (argc < 2)
+		return -1;
+	mt = mnt_new_mtab(MNT_ACT_UMOUNT);
+	if (!mt)
+		return -1;
+	mnt_mtab_set_target(mt, argv[1]);
+
+	rc = update(mt);
+
+	mnt_free_mtab(mt);
+	return rc;
+}
+
+int test_move(struct mtest *ts, int argc, char *argv[])
+{
+	mnt_mtab *mt;
+	int rc = -1;
+
+	if (argc < 3)
+		return -1;
+	mt = mnt_new_mtab(MNT_ACT_MOUNT);
+	if (!mt)
+		return -1;
+	mnt_mtab_set_mountflags(mt, MS_MOVE);
+	mnt_mtab_set_old_target(mt, argv[1]);
+	mnt_mtab_set_target(mt, argv[2]);
+
+	rc = update(mt);
+
+	mnt_free_mtab(mt);
+	return rc;
+}
+
+int test_remount(struct mtest *ts, int argc, char *argv[])
+{
+	mnt_mtab *mt;
+	int rc = -1;
+
+	if (argc < 3)
+		return -1;
+	mt = mnt_new_mtab(MNT_ACT_MOUNT);
+	if (!mt)
+		return -1;
+	mnt_mtab_set_mountflags(mt, MS_REMOUNT);
+	mnt_mtab_set_target(mt, argv[1]);
+	mnt_mtab_set_optstr(mt, argv[2]);
+
+	rc = update(mt);
+
+	mnt_free_mtab(mt);
+	return rc;
+}
+
+int main(int argc, char *argv[])
+{
+	struct mtest tss[] = {
+	{ "--add",    test_add,     "<src> <target> <type> <options>  add line to mtab" },
+	{ "--remove", test_remove,  "<target>                      MS_REMOUNT mtab change" },
+	{ "--move",   test_move,    "<old_target>  <target>        MS_MOVE mtab change" },
+	{ "--remount",test_remount, "<target>  <options>           MS_REMOUNT mtab change" },
+	{ NULL }
+	};
+
+	return mnt_run_test(tss, argc, argv);
+}
+
+#endif /* TEST_PROGRAM */