libmount: add umount(2) support

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

6 files changed, 709 insertions, 91 deletions

diff --git a/shlibs/mount/src/Makefile.am b/shlibs/mount/src/Makefile.am
index f1db1ad1b..820ab8bc0 100644
--- a/shlibs/mount/src/Makefile.am
+++ b/shlibs/mount/src/Makefile.am
@@ -12,7 +12,7 @@ usrlib_exec_LTLIBRARIES = libmount.la
 libmount_la_SOURCES =	mountP.h version.c utils.c test.c init.c cache.c \
 			optstr.c optmap.c iter.c lock.c \
 			fs.c tab.c tab_parse.c tab_update.c \
-			context.c context_mount.c \
+			context.c context_mount.c context_umount.c \
 			$(mountinc_HEADERS) \
 			$(top_srcdir)/lib/at.c \
 			$(top_srcdir)/include/list.h \
diff --git a/shlibs/mount/src/context.c b/shlibs/mount/src/context.c
index bf364a498..08d4e1e86 100644
--- a/shlibs/mount/src/context.c
+++ b/shlibs/mount/src/context.c
@@ -218,6 +218,21 @@ int mnt_context_enable_lazy(mnt_context *cxt, int enable)
 }
 
 /**
+ * mnt_context_enable_rdonly_umount:
+ * @cxt: mount context
+ * @enable: TRUE or FALSE
+ *
+ * Enable/disable read-only remount on failed umount(2)
+ * (see umount(8) man page, option -r).
+ *
+ * Returns: 0 on success, negative number in case of error.
+ */
+int mnt_context_enable_rdonly_umount(mnt_context *cxt, int enable)
+{
+	return set_flag(cxt, MNT_FL_RDONLY_UMOUNT, enable);
+}
+
+/**
  * mnt_context_disable_helpers:
  * @cxt: mount context
  * @disable: TRUE or FALSE
@@ -568,7 +583,7 @@ int mnt_context_get_mtab(mnt_context *cxt, mnt_tab **tb)
 		int rc;
 
 		cxt->mtab = mnt_new_tab();
-		if (!cxt->fstab)
+		if (!cxt->mtab)
 			return -ENOMEM;
 		rc = mnt_tab_parse_mtab(cxt->mtab);
 		if (rc)
@@ -980,6 +995,11 @@ int mnt_context_prepare_helper(mnt_context *cxt, const char *name,
 int mnt_context_prepare_update(mnt_context *cxt, int act)
 {
 	int rc;
+	const char *tgt = cxt->fs ? mnt_fs_get_target(cxt->fs) : NULL;
+
+	if (act == MNT_ACT_UMOUNT && tgt && !strcmp(tgt, "/"))
+		/* Don't try to touch mtab if umounting root FS */
+		cxt->flags |= MNT_FL_NOMTAB;
 
 	if ((cxt->flags & MNT_FL_NOMTAB) || cxt->helper)
 		return 0;
@@ -1131,3 +1151,146 @@ err:
 	DBG(CXT, mnt_debug_h(cxt, "failed to found entry in fstab/mtab"));
 	return rc;
 }
+
+
+#ifdef TEST_PROGRAM
+
+mnt_lock *lock;
+
+static void lock_fallback(void)
+{
+	if (lock) {
+		mnt_unlock_file(lock);
+		mnt_free_lock(lock);
+	}
+}
+
+int test_mount(struct mtest *ts, int argc, char *argv[])
+{
+	int idx = 1, rc = 0;
+	mnt_context *cxt;
+
+	if (argc < 2)
+		return -EINVAL;
+
+	cxt = mnt_new_context();
+	if (!cxt)
+		return -ENOMEM;
+
+	if (!strcmp(argv[idx], "-o")) {
+		mnt_context_set_optstr(cxt, argv[idx + 1]);
+		idx += 2;
+	}
+	if (!strcmp(argv[idx], "-t")) {
+		/* TODO: use mnt_context_set_fstype_pattern() */
+		mnt_context_set_fstype(cxt, argv[idx + 1]);
+		idx += 2;
+	}
+
+	if (argc == idx + 1)
+		/* mount <mountpont>|<device> */
+		mnt_context_set_target(cxt, argv[idx++]);
+
+	else if (argc == idx + 2) {
+		/* mount <device> <mountpoint> */
+		mnt_context_set_source(cxt, argv[idx++]);
+		mnt_context_set_target(cxt, argv[idx++]);
+	}
+
+	rc = mnt_context_prepare_mount(cxt);
+	if (rc)
+		printf("failed to prepare mount\n");
+	else {
+		lock = mnt_context_get_lock(cxt);
+		if (lock)
+			atexit(lock_fallback);
+
+		rc = mnt_context_do_mount(cxt);
+		if (rc)
+			printf("failed to mount\n");
+		else {
+			printf("successfully mounted");
+			rc = mnt_context_post_mount(cxt);
+			if (rc)
+				printf("mtab update failed\n");
+		}
+	}
+
+	mnt_free_context(cxt);
+	return rc;
+}
+
+int test_umount(struct mtest *ts, int argc, char *argv[])
+{
+	int idx = 1, rc = 0;
+	mnt_context *cxt;
+
+	if (argc < 2)
+		return -EINVAL;
+
+	cxt = mnt_new_context();
+	if (!cxt)
+		return -ENOMEM;
+
+	if (!strcmp(argv[idx], "-t")) {
+		mnt_context_set_fstype(cxt, argv[idx + 1]);
+		idx += 2;
+	}
+
+	if (!strcmp(argv[idx], "-f")) {
+		mnt_context_enable_force(cxt, TRUE);
+		idx++;
+	}
+
+	if (!strcmp(argv[idx], "-l")) {
+		mnt_context_enable_lazy(cxt, TRUE);
+		idx++;
+	}
+
+	if (!strcmp(argv[idx], "-r")) {
+		mnt_context_enable_rdonly_umount(cxt, TRUE);
+		idx++;
+	}
+
+	if (argc == idx + 1) {
+		/* mount <mountpont>|<device> */
+		mnt_context_set_target(cxt, argv[idx++]);
+	} else {
+		rc = -EINVAL;
+		goto err;
+	}
+
+	rc = mnt_context_prepare_umount(cxt);
+	if (rc)
+		printf("failed to prepare umount\n");
+	else {
+		lock = mnt_context_get_lock(cxt);
+		if (lock)
+			atexit(lock_fallback);
+
+		rc = mnt_context_do_umount(cxt);
+		if (rc)
+			printf("failed to umount\n");
+		else {
+			printf("successfully umounted");
+			rc = mnt_context_post_umount(cxt);
+			if (rc)
+				printf("mtab update failed\n");
+		}
+	}
+err:
+	mnt_free_context(cxt);
+	return rc;
+}
+
+int main(int argc, char *argv[])
+{
+	struct mtest tss[] = {
+	{ "--mount",  test_mount,  "[-o <opts>] [-t <type>] <spec>|<src> <target>" },
+	{ "--umount", test_umount, "[-t <type>] [-f][-l][-r] <src>|<target>" },
+	{ NULL }};
+
+	return mnt_run_test(tss, argc, argv);
+}
+
+#endif /* TEST_PROGRAM */
diff --git a/shlibs/mount/src/context_mount.c b/shlibs/mount/src/context_mount.c
index a09eee936..4bfdb267c 100644
--- a/shlibs/mount/src/context_mount.c
+++ b/shlibs/mount/src/context_mount.c
@@ -246,7 +246,7 @@ static int exec_helper(mnt_context *cxt)
 
 	rc = generate_helper_optstr(cxt, &o);
 	if (rc)
-		goto done;
+		return -EINVAL;
 
 	DBG_FLUSH;
 
@@ -313,8 +313,6 @@ static int exec_helper(mnt_context *cxt)
 		break;
 	}
 
-done:
-	free(o);
 	return rc;
 }
 
@@ -351,20 +349,22 @@ static int do_mount(mnt_context *cxt, const char *try_type)
 	if (!(flags & MS_MGC_MSK))
 		flags |= MS_MGC_VAL;
 
-	DBG(CXT, mnt_debug_h(cxt, "calling mount(2) "
+	DBG(CXT, mnt_debug_h(cxt, "%smount(2) "
 			"[source=%s, target=%s, type=%s, "
 			" mountflags=%08lx, mountdata=%s]",
+			(cxt->flags & MNT_FL_FAKE) ? "(FAKE) " : "",
 			src, target, type,
 			flags, cxt->mountdata ? "yes" : "<none>"));
 
-	if (mount(src, target, type, flags, cxt->mountdata)) {
-		cxt->syscall_errno = errno;
-		DBG(CXT, mnt_debug_h(cxt, "mount(2) failed [errno=%d]",
-						cxt->syscall_errno));
-		return -cxt->syscall_errno;
+	if (!(cxt->flags & MNT_FL_FAKE)) {
+		if (mount(src, target, type, flags, cxt->mountdata)) {
+			cxt->syscall_errno = errno;
+			DBG(CXT, mnt_debug_h(cxt, "mount(2) failed [errno=%d]",
+							cxt->syscall_errno));
+			return -cxt->syscall_errno;
+		}
+		DBG(CXT, mnt_debug_h(cxt, "mount(2) success"));
 	}
-
-	DBG(CXT, mnt_debug_h(cxt, "mount(2) success"));
 	return 0;
 }
 
@@ -502,81 +502,3 @@ int mnt_context_mount_strerror(mnt_context *cxt, char *buf, size_t bufsiz)
 	return 0;
 }
 
-#ifdef TEST_PROGRAM
-
-mnt_lock *lock;
-
-static void lock_fallback(void)
-{
-	if (lock) {
-		mnt_unlock_file(lock);
-		mnt_free_lock(lock);
-	}
-}
-
-int test_mount(struct mtest *ts, int argc, char *argv[])
-{
-	int idx = 1, rc = 0;
-	mnt_context *cxt;
-
-	if (argc < 2)
-		return -EINVAL;
-
-	cxt = mnt_new_context();
-	if (!cxt)
-		return -ENOMEM;
-
-	if (!strcmp(argv[idx], "-o")) {
-		mnt_context_set_optstr(cxt, argv[idx + 1]);
-		idx += 2;
-	}
-	if (!strcmp(argv[idx], "-t")) {
-		/* TODO: use mnt_context_set_fstype_pattern() */
-		mnt_context_set_fstype(cxt, argv[idx + 1]);
-		idx += 2;
-	}
-
-	if (argc == idx + 1)
-		/* mount <mountpont>|<device> */
-		mnt_context_set_target(cxt, argv[idx++]);
-
-	else if (argc == idx + 2) {
-		/* mount <device> <mountpoint> */
-		mnt_context_set_source(cxt, argv[idx++]);
-		mnt_context_set_target(cxt, argv[idx++]);
-	}
-
-	rc = mnt_context_prepare_mount(cxt);
-	if (rc)
-		printf("failed to prepare mount\n");
-	else {
-		lock = mnt_context_get_lock(cxt);
-		if (lock)
-			atexit(lock_fallback);
-
-		rc = mnt_context_do_mount(cxt);
-		if (rc)
-			printf("failed to mount\n");
-		else {
-			printf("successfully mounted");
-			rc = mnt_context_post_mount(cxt);
-			if (rc)
-				printf("mtab update failed\n");
-		}
-	}
-
-	mnt_free_context(cxt);
-	return rc;
-}
-
-int main(int argc, char *argv[])
-{
-	struct mtest tss[] = {
-	{ "--mount",    test_mount,        "[-o <opts>] [-t <type>] <spec> | <src> <target>" },
-	{ NULL }
-	};
-
-	return mnt_run_test(tss, argc, argv);
-}
-
-#endif /* TEST_PROGRAM */
diff --git a/shlibs/mount/src/context_umount.c b/shlibs/mount/src/context_umount.c
new file mode 100644
index 000000000..1222fe6f9
--- /dev/null
+++ b/shlibs/mount/src/context_umount.c
@@ -0,0 +1,529 @@
+/*
+ * Copyright (C) 2010 Karel Zak <kzak@redhat.com>
+ *
+ * This file may be redistributed under the terms of the
+ * GNU Lesser General Public License.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+#include <sys/wait.h>
+#include <sys/mount.h>
+
+#include "c.h"
+#include "pathnames.h"
+#include "strutils.h"
+#include "mountP.h"
+
+static int lookup_umount_fs(mnt_context *cxt)
+{
+	int rc;
+	const char *tgt;
+	mnt_tab *mtab;
+	mnt_fs *fs;
+
+	tgt = mnt_fs_get_target(cxt->fs);
+	if (!tgt) {
+		DBG(CXT, mnt_debug_h(cxt, "umount: undefined target"));
+		return -EINVAL;
+	}
+	rc = mnt_context_get_mtab(cxt, &mtab);
+	if (rc) {
+		DBG(CXT, mnt_debug_h(cxt, "umount: failed to read mtab"));
+		return rc;
+	}
+	fs = mnt_tab_find_target(mtab, tgt, MNT_ITER_BACKWARD);
+	if (!fs) {
+		/* maybe the option is source rather than target (mountpoint) */
+		fs = mnt_tab_find_source(mtab, tgt, MNT_ITER_BACKWARD);
+
+		if (fs) {
+			mnt_fs *fs1 = mnt_tab_find_target(mtab,
+							mnt_fs_get_target(fs),
+							MNT_ITER_BACKWARD);
+			if (!fs1) {
+				DBG(CXT, mnt_debug_h(cxt, "mtab is broken?!?!"));
+				return -EINVAL;
+			}
+			if (fs != fs1) {
+				/* Something was stacked over `file' on the
+				 * same mount point. */
+				DBG(CXT, mnt_debug_h(cxt,
+						"umount: %s: %s is mounted "
+						"over it on the same point",
+						tgt, mnt_fs_get_source(fs1)));
+				return -EINVAL;
+			}
+		}
+	}
+
+	if (!fs) {
+		DBG(CXT, mnt_debug_h(cxt, "cannot found %s in mtab", tgt));
+		return 0;
+	}
+
+	/* copy from mtab/fstab to our FS description
+	 */
+	rc = mnt_fs_set_source(cxt->fs, mnt_fs_get_source(fs));
+	if (!rc)
+		rc = mnt_fs_set_target(cxt->fs, mnt_fs_get_target(fs));
+
+	if (!rc && !mnt_fs_get_fstype(cxt->fs))
+		rc = mnt_fs_set_fstype(cxt->fs, mnt_fs_get_fstype(fs));
+	if (!rc)
+		rc = mnt_fs_set_optstr(cxt->fs, mnt_fs_get_optstr(fs));
+
+	cxt->flags |= MNT_FL_TAB_APPLIED;
+	return rc;
+}
+
+/* check if @devname is loopdev and if the device is associated
+ * with a source from @fstab_fs
+ *
+ * TODO : move this to loopdev.c
+ */
+static int mnt_loopdev_associated_fs(const char *devname, mnt_fs *fs)
+{
+	uintmax_t offset = 0;
+	const char *src;
+	char *val, *optstr;
+	size_t valsz;
+
+	/* check if it begins with /dev/loop */
+	if (strncmp(devname, _PATH_DEV_LOOP, sizeof(_PATH_DEV_LOOP)))
+		return 0;
+
+	src = mnt_fs_get_srcpath(fs);
+	if (!src)
+		return 0;
+
+	/* check for offset option in @fs */
+	optstr = (char *) mnt_fs_get_optstr(fs);
+	if (optstr && !mnt_optstr_get_option(optstr, "offset=", &val, &valsz)) {
+		int rc;
+
+		val = strndup(val, valsz);
+		if (!val)
+			return 0;
+		rc = strtosize(val, &offset);
+		free(val);
+		if (rc)
+			return 0;
+	}
+
+	/* TODO:
+	 * if (mnt_loopdev_associated_file(devname, src, offset))
+	 *	return 1;
+	 */
+	return 0;
+}
+
+/*
+ * Note that cxt->fs contains relevant mtab entry!
+ */
+static int evaluate_permissions(mnt_context *cxt)
+{
+	mnt_tab *fstab;
+	unsigned long u_flags;
+	const char *tgt, *src, *optstr;
+	int rc, ok = 0;
+	mnt_fs *fs;
+
+	if (!cxt || !cxt->fs)
+		return -EINVAL;
+
+	if (!mnt_context_is_restricted(cxt))
+		 return 0;		/* superuser mount */
+
+	if (!(cxt->flags & MNT_FL_TAB_APPLIED)) {
+		DBG(CXT, mnt_debug_h(cxt,
+				"cannot found %s in mtab and you are not root",
+				mnt_fs_get_target(cxt->fs)));
+		goto eperm;
+	}
+
+	mnt_context_get_userspace_mountflags(cxt, &u_flags);
+
+	if (!(cxt->flags & MNT_FL_NOHELPERS) && (u_flags & MNT_MS_UHELPER)) {
+		char *suffix = NULL;
+		char *o = (char *) mnt_fs_get_optstr(cxt->fs);
+		size_t valsz;
+
+		rc = mnt_optstr_get_option(o, "uhelper", &suffix, &valsz);
+		if (!rc) {
+			suffix = strndup(suffix, valsz);
+			if (!suffix)
+				return -ENOMEM;
+			rc = mnt_context_prepare_helper(cxt, "umount", suffix);
+		}
+		if (rc < 0)
+			return rc;
+		if (cxt->helper)
+			return 0;	/* we'll call /sbin/umount.<uhelper> */
+	}
+
+	/*
+	 * User mounts has to be in /etc/fstab
+	 */
+	rc = mnt_context_get_fstab(cxt, &fstab);
+	if (rc)
+		return rc;
+
+	tgt = mnt_fs_get_target(cxt->fs);
+	src = mnt_fs_get_source(cxt->fs);
+
+	/* If fstab contains the two lines
+	 *	/dev/sda1 /mnt/zip auto user,noauto  0 0
+	 *	/dev/sda4 /mnt/zip auto user,noauto  0 0
+	 * then "mount /dev/sda4" followed by "umount /mnt/zip" used to fail.
+	 * So, we must not look for file, but for the pair (dev,file) in fstab.
+	  */
+	fs = mnt_tab_find_pair(fstab, src, tgt, MNT_ITER_FORWARD);
+	if (!fs) {
+		/*
+		 * It's possible that there is /path/file.img in fstab and
+		 * /dev/loop0 in mtab -- then we have to check releation
+		 * between loopdev and the file.
+		 */
+		fs = mnt_tab_find_target(fstab, tgt, MNT_ITER_FORWARD);
+		if (fs) {
+			const char *dev = mnt_fs_get_srcpath(cxt->fs);		/* devname from mtab */
+
+			if (!dev || !mnt_loopdev_associated_fs(dev, fs))
+				fs = NULL;
+		}
+		if (!fs) {
+			DBG(CXT, mnt_debug_h(cxt,
+					"umount %s: mtab disagrees with fstab",
+					tgt));
+			goto eperm;
+		}
+	}
+
+	/*
+	 * User mounting and unmounting is allowed only if fstab contains one
+	 * of the options `user', `users' or `owner' or `group'.
+	 *
+	 * The option `users' allows arbitrary users to mount and unmount -
+	 * this may be a security risk.
+	 *
+	 * The options `user', `owner' and `group' only allow unmounting by the
+	 * user that mounted (visible in mtab).
+	 */
+	optstr = mnt_fs_get_optstr(fs);
+	if (!optstr)
+		goto eperm;
+
+	if (mnt_optstr_get_userspace_mountflags(optstr, &u_flags))
+		goto eperm;
+
+	if (u_flags & MNT_MS_USERS)
+		/* promiscuous setting in fstab */
+		return 0;
+	/*
+	 * Check user=<username> setting from mtab if there is user, owner or
+	 * group option in /etc/fstab
+	 */
+	if ((u_flags & MNT_MS_USER) || (u_flags & MNT_MS_OWNER) ||
+	    (u_flags & MNT_MS_GROUP)) {
+
+		char *curr_user = mnt_get_username(getuid());
+		char *mtab_user = NULL;
+		size_t sz;
+
+		if (!curr_user) {
+			DBG(CXT, mnt_debug_h(cxt, "umount %s: cannot "
+					"convert %d to username",
+					tgt, getuid()));
+			goto eperm;
+		}
+
+		/* get options from mtab */
+		optstr = mnt_fs_get_optstr(cxt->fs);
+		if (optstr && !mnt_optstr_get_option((char *) optstr,
+					"user", &mtab_user, &sz) && sz)
+			ok = !strncmp(curr_user, mtab_user, sz);
+	}
+
+	if (ok) {
+		DBG(CXT, mnt_debug_h(cxt, "umount %s is allowed", tgt));
+		return 0;
+	}
+eperm:
+	DBG(CXT, mnt_debug_h(cxt, "umount %s is not allowed for you", tgt));
+	return -EPERM;
+}
+
+static int exec_helper(mnt_context *cxt)
+{
+	int rc;
+
+	assert(cxt);
+	assert(cxt->fs);
+	assert(cxt->helper);
+
+	DBG_FLUSH;
+
+	switch (fork()) {
+	case 0:
+	{
+		const char *args[10], *type;
+		int i = 0;
+
+		if (setgid(getgid()) < 0)
+			exit(EXIT_FAILURE);
+
+		if (setuid(getuid()) < 0)
+			exit(EXIT_FAILURE);
+
+		type = mnt_fs_get_fstype(cxt->fs);
+
+		args[i++] = cxt->helper;			/* 1 */
+		args[i++] = mnt_fs_get_target(cxt->fs);		/* 2 */
+
+		if (cxt->flags & MNT_FL_NOMTAB)
+			args[i++] = "-n";			/* 3 */
+		if (cxt->flags & MNT_FL_LAZY)
+			args[i++] = "-l";			/* 4 */
+		if (cxt->flags & MNT_FL_FORCE)
+			args[i++] = "-f";			/* 5 */
+		if (cxt->flags & MNT_FL_VERBOSE)
+			args[i++] = "-v";			/* 6 */
+		if (cxt->flags & MNT_FL_RDONLY_UMOUNT)
+			args[i++] = "-r";			/* 7 */
+		if (type && !endswith(cxt->helper, type)) {
+			args[i++] = "-t";			/* 8 */
+			args[i++] = (char *) type;	/* 9 */
+		}
+
+		args[i] = NULL;					/* 10 */
+#ifdef CONFIG_LIBMOUNT_DEBUG
+		i = 0;
+		for (i = 0; args[i]; i++)
+			DBG(CXT, mnt_debug_h(cxt, "argv[%d] = \"%s\"",
+							i, args[i]));
+#endif
+		DBG_FLUSH;
+		execv(cxt->helper, (char * const *) args);
+		exit(EXIT_FAILURE);
+	}
+	default:
+	{
+		int st;
+		wait(&st);
+		cxt->helper_status = WIFEXITED(st) ? WEXITSTATUS(st) : -1;
+
+		DBG(CXT, mnt_debug_h(cxt, "%s executed [status=%d]",
+					cxt->helper, cxt->helper_status));
+		rc = 0;
+		break;
+	}
+
+	case -1:
+		rc = -errno;
+		DBG(CXT, mnt_debug_h(cxt, "fork() failed"));
+		break;
+	}
+
+	return rc;
+}
+
+static int do_umount(mnt_context *cxt)
+{
+	int rc = 0;
+	const char *src, *target;
+
+	assert(cxt);
+	assert(cxt->fs);
+
+	if (cxt->helper)
+		return exec_helper(cxt);
+
+	src = mnt_fs_get_srcpath(cxt->fs);
+	target = mnt_fs_get_target(cxt->fs);
+
+	if (!target)
+		return -EINVAL;
+
+	if (cxt->flags & MNT_FL_FAKE)
+		return 0;
+
+	if (cxt->flags & MNT_FL_LAZY)
+		rc = umount2(target, MNT_DETACH);
+
+	else if (cxt->flags & MNT_FL_FORCE) {
+		rc = umount2(target, MNT_FORCE);
+
+		if (rc < 0 && errno == ENOSYS)
+			rc = umount(target);
+	} else
+		rc = umount(target);
+
+	if (rc < 0)
+		cxt->syscall_errno = errno;
+
+	/*
+	 * try remount read-only
+	 */
+	if (rc < 0 && cxt->syscall_errno == EBUSY &&
+	    (cxt->flags & MNT_FL_RDONLY_UMOUNT) && src) {
+
+		cxt->mountflags |= MS_REMOUNT | MS_RDONLY;
+		cxt->flags &= ~MNT_FL_LOOPDEL;
+		DBG(CXT, mnt_debug_h(cxt, "umount(2) failed [errno=%d] -- "
+					"tring remount read-only",
+					cxt->syscall_errno));
+
+		rc = mount(src, target, NULL,
+			    MS_MGC_VAL | MS_REMOUNT | MS_RDONLY, NULL);
+		if (rc < 0) {
+			cxt->syscall_errno = errno;
+			DBG(CXT, mnt_debug_h(cxt, "read-only re-mount(2) failed "
+					"[errno=%d]",
+					cxt->syscall_errno));
+			return -cxt->syscall_errno;
+		}
+		cxt->syscall_errno = 0;
+		DBG(CXT, mnt_debug_h(cxt, "read-only re-mount(2) success"));
+		return 0;
+	}
+
+	if (rc < 0) {
+		DBG(CXT, mnt_debug_h(cxt, "umount(2) failed [errno=%d]",
+					cxt->syscall_errno));
+		return -cxt->syscall_errno;
+	}
+	DBG(CXT, mnt_debug_h(cxt, "umount(2) success"));
+	return 0;
+}
+
+/**
+ * mnt_context_prepare_umount:
+ * @cxt: mount context
+ *
+ * This function:
+ *	- read information from fstab/mtab (if necessary)
+ *	- check premissions
+ *	- prepare for mtab update (if necessary)
+ *
+ * It's strongly recommended to use this function before mnt_context_do_umount().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_prepare_umount(mnt_context *cxt)
+{
+	int rc = 0;
+
+	if (!cxt)
+		return -EINVAL;
+
+	if (!cxt->fs || (!mnt_fs_get_source(cxt->fs) &&
+			 !mnt_fs_get_target(cxt->fs)))
+		return -EINVAL;
+
+	free(cxt->helper);	/* be paranoid */
+	cxt->helper = NULL;
+
+	rc = lookup_umount_fs(cxt);
+	if (!rc)
+		rc = evaluate_permissions(cxt);
+	if (!rc && !cxt->helper)
+		rc = mnt_context_prepare_helper(cxt, "umount", NULL);
+/* TODO
+	if ((cxt->flags & MNT_FL_LOOPDEL) &&
+	    (!mnt_is_loopdev(src) || mnt_loopdev_is_autoclear(src)))
+		cxt->flags &= ~MNT_FL_LOOPDEL;
+*/
+	if (!rc)
+		rc = mnt_context_prepare_update(cxt, MNT_ACT_UMOUNT);
+	if (!rc) {
+		DBG(CXT, mnt_debug_h(cxt, "umount sucessfully prepared"));
+		return 0;
+	}
+
+	DBG(CXT, mnt_debug_h(cxt, "umount prepare failed"));
+	return rc;
+}
+
+/**
+ * mnt_context_do_umount:
+ * @cxt: mount context
+ *
+ * Umount filesystem by umount(2) or fork()+exec(/sbin/umount.<type>).
+ *
+ * See also mnt_context_disable_helpers().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_do_umount(mnt_context *cxt)
+{
+	if (!cxt || !cxt->fs || (cxt->fs->flags & MNT_FS_SWAP))
+		return -EINVAL;
+
+	return do_umount(cxt);
+}
+
+/**
+ * mnt_context_post_umount:
+ * @cxt: mount context
+ *
+ * Updates mtab and detroy loopdev etc. This function should be always called after
+ * mnt_context_do_umount().
+ *
+ * Returns: 0 on success, and negative number in case of error.
+ */
+int mnt_context_post_umount(mnt_context *cxt)
+{
+	int rc = 0;
+
+	if (!cxt)
+		return -EINVAL;
+	if (cxt->syscall_errno || cxt->helper)
+		return 0;
+/* TODO
+	if (cxt->flags & MNT_FL_LOOPDEL)
+		rc = mnt_loopdev_clean(mnt_fs_get_source(cxt->fs));
+*/
+	if (cxt->flags & MNT_FL_NOMTAB)
+		return rc;
+
+	if ((cxt->flags & MNT_FL_RDONLY_UMOUNT) &&
+	    (cxt->mountflags & (MS_RDONLY | MS_REMOUNT))) {
+		/*
+		 * refresh update to handle remount to read-only
+		 */
+		rc = mnt_context_prepare_update(cxt, MNT_ACT_MOUNT);
+		if (rc)
+			return rc;
+	}
+
+	/*
+	 * Update /etc/mtab or /var/run/mount/mountinfo
+	 */
+	if (cxt->update && !mnt_update_is_pointless(cxt->update)) {
+		rc = mnt_update_file(cxt->update);
+		if (!rc)
+			return rc;
+	}
+	return rc;
+}
+
+/**
+ * mnt_context_umount_strerror
+ * @cxt: mount context
+ * @buf: buffer
+ * @bufsiz: size of the buffer
+ *
+ * Returns: 0 or negative number in case of error.
+ */
+int mnt_context_umount_strerror(mnt_context *cxt, char *buf, size_t bufsiz)
+{
+	/* TODO: based on cxt->syscall_errno or cxt->helper_status */
+	return 0;
+}
diff --git a/shlibs/mount/src/mount.h.in b/shlibs/mount/src/mount.h.in
index 43f81080d..f4b4e6ad4 100644
--- a/shlibs/mount/src/mount.h.in
+++ b/shlibs/mount/src/mount.h.in
@@ -326,6 +326,7 @@ extern int mnt_context_disable_lock(mnt_context *cxt, int disable);
 extern int mnt_context_enable_force(mnt_context *cxt, int enable);
 extern int mnt_context_enable_verbose(mnt_context *cxt, int enable);
 extern int mnt_context_enable_loopdel(mnt_context *cxt, int enable);
+extern int mnt_context_enable_rdonly_umount(mnt_context *cxt, int enable);
 extern int mnt_context_set_fs(mnt_context *cxt, mnt_fs *fs);
 extern int mnt_context_set_source(mnt_context *cxt, const char *source);
 extern int mnt_context_set_target(mnt_context *cxt, const char *target);
@@ -335,6 +336,8 @@ extern int mnt_context_append_optstr(mnt_context *cxt, const char *optstr);
 extern int mnt_context_set_fstype_pattern(mnt_context *cxt, const char *pattern);
 extern int mnt_context_set_optstr_pattern(mnt_context *cxt, const char *pattern);
 extern int mnt_context_set_fstab(mnt_context *cxt, mnt_tab *tb);
+extern int mnt_context_get_fstab(mnt_context *cxt, mnt_tab **tb);
+extern int mnt_context_get_mtab(mnt_context *cxt, mnt_tab **tb);
 extern int mnt_context_set_cache(mnt_context *cxt, mnt_cache *cache);
 extern mnt_cache *mnt_context_get_cache(mnt_context *cxt);
 extern mnt_lock *mnt_context_get_lock(mnt_context *cxt);
diff --git a/shlibs/mount/src/mountP.h b/shlibs/mount/src/mountP.h
index 96490b160..9f05cf555 100644
--- a/shlibs/mount/src/mountP.h
+++ b/shlibs/mount/src/mountP.h
@@ -250,6 +250,7 @@ struct _mnt_context
 #define MNT_FL_FORCE		(1 << 8)
 #define MNT_FL_NOCANONICALIZE	(1 << 9)
 #define MNT_FL_NOLOCK		(1 << 10)	/* don't lock mtab file */
+#define MNT_FL_RDONLY_UMOUNT	(1 << 11)	/* remount,ro after EBUSY umount(2) */
 
 #define MNT_FL_EXTERN_FS	(1 << 15)	/* cxt->fs is not private */
 #define MNT_FL_EXTERN_FSTAB	(1 << 16)	/* cxt->fstab is not private */