Adding upstream version 2.38.1.upstream/2.38.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 980 insertions, 0 deletions

diff --git a/libmount/src/monitor.c b/libmount/src/monitor.c
new file mode 100644
index 0000000..dada02e
--- /dev/null
+++ b/libmount/src/monitor.c
@@ -0,0 +1,980 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * This file is part of libmount from util-linux project.
+ *
+ * Copyright (C) 2014-2018 Karel Zak <kzak@redhat.com>
+ *
+ * libmount is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ */
+
+/**
+ * SECTION: monitor
+ * @title: Monitor
+ * @short_description: interface to monitor mount tables
+ *
+ * For example monitor VFS (/proc/self/mountinfo) for changes:
+ *
+ * <informalexample>
+ *   <programlisting>
+ * const char *filename;
+ * struct libmount_monitor *mn = mnt_new_monitor();
+ *
+ * mnt_monitor_enable_kernel(mn, TRUE));
+ *
+ * printf("waiting for changes...\n");
+ * while (mnt_monitor_wait(mn, -1) > 0) {
+ *    while (mnt_monitor_next_change(mn, &filename, NULL) == 0)
+ *       printf(" %s: change detected\n", filename);
+ * }
+ * mnt_unref_monitor(mn);
+ *   </programlisting>
+ * </informalexample>
+ *
+ */
+
+#include "fileutils.h"
+#include "mountP.h"
+#include "pathnames.h"
+
+#include <sys/inotify.h>
+#include <sys/epoll.h>
+
+
+struct monitor_opers;
+
+struct monitor_entry {
+	int			fd;		/* private entry file descriptor */
+	char			*path;		/* path to the monitored file */
+	int			type;		/* MNT_MONITOR_TYPE_* */
+	uint32_t		events;		/* wanted epoll events */
+
+	const struct monitor_opers *opers;
+
+	unsigned int		enable : 1,
+				changed : 1;
+
+	struct list_head	ents;
+};
+
+struct libmnt_monitor {
+	int			refcount;
+	int			fd;		/* public monitor file descriptor */
+
+	struct list_head	ents;
+};
+
+struct monitor_opers {
+	int (*op_get_fd)(struct libmnt_monitor *, struct monitor_entry *);
+	int (*op_close_fd)(struct libmnt_monitor *, struct monitor_entry *);
+	int (*op_event_verify)(struct libmnt_monitor *, struct monitor_entry *);
+};
+
+static int monitor_modify_epoll(struct libmnt_monitor *mn,
+				struct monitor_entry *me, int enable);
+
+/**
+ * mnt_new_monitor:
+ *
+ * The initial refcount is 1, and needs to be decremented to
+ * release the resources of the filesystem.
+ *
+ * Returns: newly allocated struct libmnt_monitor.
+ */
+struct libmnt_monitor *mnt_new_monitor(void)
+{
+	struct libmnt_monitor *mn = calloc(1, sizeof(*mn));
+	if (!mn)
+		return NULL;
+
+	mn->refcount = 1;
+	mn->fd = -1;
+	INIT_LIST_HEAD(&mn->ents);
+
+	DBG(MONITOR, ul_debugobj(mn, "alloc"));
+	return mn;
+}
+
+/**
+ * mnt_ref_monitor:
+ * @mn: monitor pointer
+ *
+ * Increments reference counter.
+ */
+void mnt_ref_monitor(struct libmnt_monitor *mn)
+{
+	if (mn)
+		mn->refcount++;
+}
+
+static void free_monitor_entry(struct monitor_entry *me)
+{
+	if (!me)
+		return;
+	list_del(&me->ents);
+	if (me->fd >= 0)
+		close(me->fd);
+	free(me->path);
+	free(me);
+}
+
+/**
+ * mnt_unref_monitor:
+ * @mn: monitor pointer
+ *
+ * Decrements the reference counter, on zero the @mn is automatically
+ * deallocated.
+ */
+void mnt_unref_monitor(struct libmnt_monitor *mn)
+{
+	if (!mn)
+		return;
+
+	mn->refcount--;
+	if (mn->refcount <= 0) {
+		mnt_monitor_close_fd(mn);	/* destroys all file descriptors */
+
+		while (!list_empty(&mn->ents)) {
+			struct monitor_entry *me = list_entry(mn->ents.next,
+						  struct monitor_entry, ents);
+			free_monitor_entry(me);
+		}
+
+		free(mn);
+	}
+}
+
+static struct monitor_entry *monitor_new_entry(struct libmnt_monitor *mn)
+{
+	struct monitor_entry *me;
+
+	assert(mn);
+
+	me = calloc(1, sizeof(*me));
+	if (!me)
+		return NULL;
+        INIT_LIST_HEAD(&me->ents);
+	list_add_tail(&me->ents, &mn->ents);
+
+	me->fd = -1;
+
+	return me;
+}
+
+static int monitor_next_entry(struct libmnt_monitor *mn,
+			      struct libmnt_iter *itr,
+			      struct monitor_entry **me)
+{
+	int rc = 1;
+
+	assert(mn);
+	assert(itr);
+	assert(me);
+
+	*me = NULL;
+
+	if (!itr->head)
+		MNT_ITER_INIT(itr, &mn->ents);
+	if (itr->p != itr->head) {
+		MNT_ITER_ITERATE(itr, *me, struct monitor_entry, ents);
+		rc = 0;
+	}
+
+	return rc;
+}
+
+/* returns entry by type */
+static struct monitor_entry *monitor_get_entry(struct libmnt_monitor *mn, int type)
+{
+	struct libmnt_iter itr;
+	struct monitor_entry *me;
+
+	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
+	while (monitor_next_entry(mn, &itr, &me) == 0) {
+		if (me->type == type)
+			return me;
+	}
+	return NULL;
+}
+
+
+/*
+ * Userspace monitor
+ */
+
+static int userspace_monitor_close_fd(struct libmnt_monitor *mn __attribute__((__unused__)),
+				    struct monitor_entry *me)
+{
+	assert(me);
+
+	if (me->fd >= 0)
+		close(me->fd);
+	me->fd = -1;
+	return 0;
+}
+
+static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
+{
+	char *filename = NULL;
+	int wd, rc = -EINVAL;
+
+	assert(me);
+	assert(me->path);
+
+	/*
+	 * libmount uses rename(2) to atomically update utab, monitor
+	 * rename changes is too tricky. It seems better to monitor utab
+	 * lockfile close.
+	 */
+	if (asprintf(&filename, "%s.lock", me->path) <= 0) {
+		rc = -errno;
+		goto done;
+	}
+
+	/* try lock file if already exists */
+	errno = 0;
+	wd = inotify_add_watch(me->fd, filename, IN_CLOSE_NOWRITE);
+	if (wd >= 0) {
+		DBG(MONITOR, ul_debug(" added inotify watch for %s [fd=%d]", filename, wd));
+		rc = 0;
+		if (final)
+			*final = 1;
+		if (fd)
+			*fd = wd;
+		goto done;
+	} else if (errno != ENOENT) {
+		rc = -errno;
+		goto done;
+	}
+
+	while (strchr(filename, '/')) {
+		stripoff_last_component(filename);
+		if (!*filename)
+			break;
+
+		/* try directory where is the lock file */
+		errno = 0;
+		wd = inotify_add_watch(me->fd, filename, IN_CREATE|IN_ISDIR);
+		if (wd >= 0) {
+			DBG(MONITOR, ul_debug(" added inotify watch for %s [fd=%d]", filename, wd));
+			rc = 0;
+			if (fd)
+				*fd = wd;
+			break;
+		}
+
+		if (errno != ENOENT) {
+			rc = -errno;
+			break;
+		}
+	}
+done:
+	free(filename);
+	return rc;
+}
+
+static int userspace_monitor_get_fd(struct libmnt_monitor *mn,
+				    struct monitor_entry *me)
+{
+	int rc;
+
+	if (!me || me->enable == 0)	/* not-initialized or disabled */
+		return -EINVAL;
+	if (me->fd >= 0)
+		return me->fd;		/* already initialized */
+
+	assert(me->path);
+	DBG(MONITOR, ul_debugobj(mn, " open userspace monitor for %s", me->path));
+
+	me->fd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+	if (me->fd < 0)
+		goto err;
+
+	if (userspace_add_watch(me, NULL, NULL) < 0)
+		goto err;
+
+	return me->fd;
+err:
+	rc = -errno;
+	if (me->fd >= 0)
+		close(me->fd);
+	me->fd = -1;
+	DBG(MONITOR, ul_debugobj(mn, "failed to create userspace monitor [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * verify and drain inotify buffer
+ */
+static int userspace_event_verify(struct libmnt_monitor *mn,
+					struct monitor_entry *me)
+{
+	char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
+	int status = 0;
+
+	if (!me || me->fd < 0)
+		return 0;
+
+	DBG(MONITOR, ul_debugobj(mn, "drain and verify userspace monitor inotify"));
+
+	/* the me->fd is non-blocking */
+	do {
+		ssize_t len;
+		char *p;
+		const struct inotify_event *e;
+
+		len = read(me->fd, buf, sizeof(buf));
+		if (len < 0)
+			break;
+
+		for (p = buf; p < buf + len;
+		     p += sizeof(struct inotify_event) + e->len) {
+
+			int fd = -1;
+
+			e = (const struct inotify_event *) p;
+			DBG(MONITOR, ul_debugobj(mn, " inotify event 0x%x [%s]\n", e->mask, e->len ? e->name : ""));
+
+			if (e->mask & IN_CLOSE_NOWRITE)
+				status = 1;
+			else {
+				/* event on lock file */
+				userspace_add_watch(me, &status, &fd);
+
+				if (fd != e->wd) {
+					DBG(MONITOR, ul_debugobj(mn, " removing watch [fd=%d]", e->wd));
+					inotify_rm_watch(me->fd, e->wd);
+				}
+			}
+		}
+	} while (1);
+
+	DBG(MONITOR, ul_debugobj(mn, "%s", status == 1 ? " success" : " nothing"));
+	return status;
+}
+
+/*
+ * userspace monitor operations
+ */
+static const struct monitor_opers userspace_opers = {
+	.op_get_fd		= userspace_monitor_get_fd,
+	.op_close_fd		= userspace_monitor_close_fd,
+	.op_event_verify	= userspace_event_verify
+};
+
+/**
+ * mnt_monitor_enable_userspace:
+ * @mn: monitor
+ * @enable: 0 or 1
+ * @filename: overwrites default
+ *
+ * Enables or disables userspace monitoring. If the userspace monitor does not
+ * exist and enable=1 then allocates new resources necessary for the monitor.
+ *
+ * If the top-level monitor has been already created (by mnt_monitor_get_fd()
+ * or mnt_monitor_wait()) then it's updated according to @enable.
+ *
+ * The @filename is used only the first time when you enable the monitor. It's
+ * impossible to have more than one userspace monitor. The recommended is to
+ * use NULL as filename.
+ *
+ * The userspace monitor is unsupported for systems with classic regular
+ * /etc/mtab file.
+ *
+ * Return: 0 on success and <0 on error
+ */
+int mnt_monitor_enable_userspace(struct libmnt_monitor *mn, int enable, const char *filename)
+{
+	struct monitor_entry *me;
+	int rc = 0;
+
+	if (!mn)
+		return -EINVAL;
+
+	me = monitor_get_entry(mn, MNT_MONITOR_TYPE_USERSPACE);
+	if (me) {
+		rc = monitor_modify_epoll(mn, me, enable);
+		if (!enable)
+			userspace_monitor_close_fd(mn, me);
+		return rc;
+	}
+	if (!enable)
+		return 0;
+
+	DBG(MONITOR, ul_debugobj(mn, "allocate new userspace monitor"));
+
+	if (!filename)
+		filename = mnt_get_utab_path();		/* /run/mount/utab */
+	if (!filename) {
+		DBG(MONITOR, ul_debugobj(mn, "failed to get userspace mount table path"));
+		return -EINVAL;
+	}
+
+	me = monitor_new_entry(mn);
+	if (!me)
+		goto err;
+
+	me->type = MNT_MONITOR_TYPE_USERSPACE;
+	me->opers = &userspace_opers;
+	me->events = EPOLLIN;
+	me->path = strdup(filename);
+	if (!me->path)
+		goto err;
+
+	return monitor_modify_epoll(mn, me, TRUE);
+err:
+	rc = -errno;
+	free_monitor_entry(me);
+	DBG(MONITOR, ul_debugobj(mn, "failed to allocate userspace monitor [rc=%d]", rc));
+	return rc;
+}
+
+
+/*
+ * Kernel monitor
+ */
+
+static int kernel_monitor_close_fd(struct libmnt_monitor *mn __attribute__((__unused__)),
+				   struct monitor_entry *me)
+{
+	assert(me);
+
+	if (me->fd >= 0)
+		close(me->fd);
+	me->fd = -1;
+	return 0;
+}
+
+static int kernel_monitor_get_fd(struct libmnt_monitor *mn,
+				 struct monitor_entry *me)
+{
+	int rc;
+
+	if (!me || me->enable == 0)	/* not-initialized or disabled */
+		return -EINVAL;
+	if (me->fd >= 0)
+		return me->fd;		/* already initialized */
+
+	assert(me->path);
+	DBG(MONITOR, ul_debugobj(mn, " open kernel monitor for %s", me->path));
+
+	me->fd = open(me->path, O_RDONLY|O_CLOEXEC);
+	if (me->fd < 0)
+		goto err;
+
+	return me->fd;
+err:
+	rc = -errno;
+	DBG(MONITOR, ul_debugobj(mn, "failed to create kernel  monitor [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * kernel monitor operations
+ */
+static const struct monitor_opers kernel_opers = {
+	.op_get_fd		= kernel_monitor_get_fd,
+	.op_close_fd		= kernel_monitor_close_fd,
+};
+
+/**
+ * mnt_monitor_enable_kernel:
+ * @mn: monitor
+ * @enable: 0 or 1
+ *
+ * Enables or disables kernel VFS monitoring. If the monitor does not exist and
+ * enable=1 then allocates new resources necessary for the monitor.
+ *
+ * If the top-level monitor has been already created (by mnt_monitor_get_fd()
+ * or mnt_monitor_wait()) then it's updated according to @enable.
+ *
+ * Return: 0 on success and <0 on error
+ */
+int mnt_monitor_enable_kernel(struct libmnt_monitor *mn, int enable)
+{
+	struct monitor_entry *me;
+	int rc = 0;
+
+	if (!mn)
+		return -EINVAL;
+
+	me = monitor_get_entry(mn, MNT_MONITOR_TYPE_KERNEL);
+	if (me) {
+		rc = monitor_modify_epoll(mn, me, enable);
+		if (!enable)
+			kernel_monitor_close_fd(mn, me);
+		return rc;
+	}
+	if (!enable)
+		return 0;
+
+	DBG(MONITOR, ul_debugobj(mn, "allocate new kernel monitor"));
+
+	/* create a new entry */
+	me = monitor_new_entry(mn);
+	if (!me)
+		goto err;
+
+	/* If you want to use epoll FD in another epoll then top level
+	 * epoll_wait() will drain all events from low-level FD if the
+	 * low-level FD is not added with EPOLLIN. It means without EPOLLIN it
+	 * it's impossible to detect which low-level FD has been active.
+	 *
+	 * Unfortunately, use EPOLLIN for mountinfo is tricky because in this
+	 * case kernel returns events all time (we don't read from the FD).
+	 * The solution is to use also edge-triggered (EPOLLET) flag, then
+	 * kernel generate events on mountinfo changes only. The disadvantage is
+	 * that we have to drain initial event generated by EPOLLIN after
+	 * epoll_ctl(ADD). See monitor_modify_epoll().
+	 */
+	me->events = EPOLLIN | EPOLLET;
+
+	me->type = MNT_MONITOR_TYPE_KERNEL;
+	me->opers = &kernel_opers;
+	me->path = strdup(_PATH_PROC_MOUNTINFO);
+	if (!me->path)
+		goto err;
+
+	return monitor_modify_epoll(mn, me, TRUE);
+err:
+	rc = -errno;
+	free_monitor_entry(me);
+	DBG(MONITOR, ul_debugobj(mn, "failed to allocate kernel monitor [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * Add/Remove monitor entry to/from monitor epoll.
+ */
+static int monitor_modify_epoll(struct libmnt_monitor *mn,
+				struct monitor_entry *me, int enable)
+{
+	assert(mn);
+	assert(me);
+
+	me->enable = enable ? 1 : 0;
+	me->changed = 0;
+
+	if (mn->fd < 0)
+		return 0;	/* no epoll, ignore request */
+
+	if (enable) {
+		struct epoll_event ev = { .events = me->events };
+		int fd = me->opers->op_get_fd(mn, me);
+
+		if (fd < 0)
+			goto err;
+
+		DBG(MONITOR, ul_debugobj(mn, " add fd=%d (for %s)", fd, me->path));
+
+		ev.data.ptr = (void *) me;
+
+		if (epoll_ctl(mn->fd, EPOLL_CTL_ADD, fd, &ev) < 0) {
+			if (errno != EEXIST)
+				goto err;
+		}
+		if (me->events & (EPOLLIN | EPOLLET)) {
+			/* Drain initial events generated for /proc/self/mountinfo */
+			struct epoll_event events[1];
+			while (epoll_wait(mn->fd, events, 1, 0) > 0);
+		}
+	} else if (me->fd) {
+		DBG(MONITOR, ul_debugobj(mn, " remove fd=%d (for %s)", me->fd, me->path));
+		if (epoll_ctl(mn->fd, EPOLL_CTL_DEL, me->fd, NULL) < 0) {
+			if (errno != ENOENT)
+				goto err;
+		}
+	}
+
+	return 0;
+err:
+	return -errno;
+}
+
+/**
+ * mnt_monitor_close_fd:
+ * @mn: monitor
+ *
+ * Close monitor file descriptor. This is usually unnecessary, because
+ * mnt_unref_monitor() cleanups all.
+ *
+ * The function is necessary only if you want to reset monitor setting. The
+ * next mnt_monitor_get_fd() or mnt_monitor_wait() will use newly initialized
+ * monitor.  This restart is unnecessary for mnt_monitor_enable_*() functions.
+ *
+ * Returns: 0 on success, <0 on error.
+ */
+int mnt_monitor_close_fd(struct libmnt_monitor *mn)
+{
+	struct libmnt_iter itr;
+	struct monitor_entry *me;
+
+	if (!mn)
+		return -EINVAL;
+
+	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
+
+	/* disable all monitor entries */
+	while (monitor_next_entry(mn, &itr, &me) == 0) {
+
+		/* remove entry from epoll */
+		if (mn->fd >= 0)
+			monitor_modify_epoll(mn, me, FALSE);
+
+		/* close entry FD */
+		me->opers->op_close_fd(mn, me);
+	}
+
+	if (mn->fd >= 0) {
+		DBG(MONITOR, ul_debugobj(mn, "closing top-level monitor fd"));
+		close(mn->fd);
+	}
+	mn->fd = -1;
+	return 0;
+}
+
+/**
+ * mnt_monitor_get_fd:
+ * @mn: monitor
+ *
+ * The file descriptor is associated with all monitored files and it's usable
+ * for example for epoll. You have to call mnt_monitor_event_cleanup() or
+ * mnt_monitor_next_change() after each event.
+ *
+ * Returns: >=0 (fd) on success, <0 on error
+ */
+int mnt_monitor_get_fd(struct libmnt_monitor *mn)
+{
+	struct libmnt_iter itr;
+	struct monitor_entry *me;
+	int rc = 0;
+
+	if (!mn)
+		return -EINVAL;
+	if (mn->fd >= 0)
+		return mn->fd;
+
+	DBG(MONITOR, ul_debugobj(mn, "create top-level monitor fd"));
+	mn->fd = epoll_create1(EPOLL_CLOEXEC);
+	if (mn->fd < 0)
+		return -errno;
+
+	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
+
+	DBG(MONITOR, ul_debugobj(mn, "adding monitor entries to epoll (fd=%d)", mn->fd));
+	while (monitor_next_entry(mn, &itr, &me) == 0) {
+		if (!me->enable)
+			continue;
+		rc = monitor_modify_epoll(mn, me, TRUE);
+		if (rc)
+			goto err;
+	}
+
+	DBG(MONITOR, ul_debugobj(mn, "successfully created monitor"));
+	return mn->fd;
+err:
+	rc = errno ? -errno : -EINVAL;
+	close(mn->fd);
+	mn->fd = -1;
+	DBG(MONITOR, ul_debugobj(mn, "failed to create monitor [rc=%d]", rc));
+	return rc;
+}
+
+/**
+ * mnt_monitor_wait:
+ * @mn: monitor
+ * @timeout: number of milliseconds, -1 block indefinitely, 0 return immediately
+ *
+ * Waits for the next change, after the event it's recommended to use
+ * mnt_monitor_next_change() to get more details about the change and to
+ * avoid false positive events.
+ *
+ * Returns: 1 success (something changed), 0 timeout, <0 error.
+ */
+int mnt_monitor_wait(struct libmnt_monitor *mn, int timeout)
+{
+	int rc;
+	struct monitor_entry *me;
+	struct epoll_event events[1];
+
+	if (!mn)
+		return -EINVAL;
+
+	if (mn->fd < 0) {
+		rc = mnt_monitor_get_fd(mn);
+		if (rc < 0)
+			return rc;
+	}
+
+	do {
+		DBG(MONITOR, ul_debugobj(mn, "calling epoll_wait(), timeout=%d", timeout));
+		rc = epoll_wait(mn->fd, events, 1, timeout);
+		if (rc < 0)
+			return -errno;		/* error */
+		if (rc == 0)
+			return 0;		/* timeout */
+
+		me = (struct monitor_entry *) events[0].data.ptr;
+		if (!me)
+			return -EINVAL;
+
+		if (me->opers->op_event_verify == NULL ||
+		    me->opers->op_event_verify(mn, me) == 1) {
+			me->changed = 1;
+			break;
+		}
+	} while (1);
+
+	return 1;			/* success */
+}
+
+
+static struct monitor_entry *get_changed(struct libmnt_monitor *mn)
+{
+	struct libmnt_iter itr;
+	struct monitor_entry *me;
+
+	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
+	while (monitor_next_entry(mn, &itr, &me) == 0) {
+		if (me->changed)
+			return me;
+	}
+	return NULL;
+}
+
+/**
+ * mnt_monitor_next_change:
+ * @mn: monitor
+ * @filename: returns changed file (optional argument)
+ * @type: returns MNT_MONITOR_TYPE_* (optional argument)
+ *
+ * The function does not wait and it's designed to provide details about changes.
+ * It's always recommended to use this function to avoid false positives.
+ *
+ * Returns: 0 on success, 1 no change, <0 on error
+ */
+int mnt_monitor_next_change(struct libmnt_monitor *mn,
+			     const char **filename,
+			     int *type)
+{
+	int rc;
+	struct monitor_entry *me;
+
+	if (!mn || mn->fd < 0)
+		return -EINVAL;
+
+	/*
+	 * if we previously called epoll_wait() (e.g. mnt_monitor_wait()) then
+	 * info about unread change is already stored in monitor_entry.
+	 *
+	 * If we get nothing, then ask kernel.
+	 */
+	me = get_changed(mn);
+	while (!me) {
+		struct epoll_event events[1];
+
+		DBG(MONITOR, ul_debugobj(mn, "asking for next changed"));
+
+		rc = epoll_wait(mn->fd, events, 1, 0);	/* no timeout! */
+		if (rc < 0) {
+			DBG(MONITOR, ul_debugobj(mn, " *** error"));
+			return -errno;
+		}
+		if (rc == 0) {
+			DBG(MONITOR, ul_debugobj(mn, " *** nothing"));
+			return 1;
+		}
+
+		me = (struct monitor_entry *) events[0].data.ptr;
+		if (!me)
+			return -EINVAL;
+
+		if (me->opers->op_event_verify != NULL &&
+		    me->opers->op_event_verify(mn, me) != 1)
+			me = NULL;
+	}
+
+	me->changed = 0;
+
+	if (filename)
+		*filename = me->path;
+	if (type)
+		*type = me->type;
+
+	DBG(MONITOR, ul_debugobj(mn, " *** success [changed: %s]", me->path));
+	return 0;
+}
+
+/**
+ * mnt_monitor_event_cleanup:
+ * @mn: monitor
+ *
+ * This function cleanups (drain) internal buffers. It's necessary to call
+ * this function after event if you do not call mnt_monitor_next_change().
+ *
+ * Returns: 0 on success, <0 on error
+ */
+int mnt_monitor_event_cleanup(struct libmnt_monitor *mn)
+{
+	int rc;
+
+	if (!mn || mn->fd < 0)
+		return -EINVAL;
+
+	while ((rc = mnt_monitor_next_change(mn, NULL, NULL)) == 0);
+	return rc < 0 ? rc : 0;
+}
+
+#ifdef TEST_PROGRAM
+
+static struct libmnt_monitor *create_test_monitor(int argc, char *argv[])
+{
+	struct libmnt_monitor *mn;
+	int i;
+
+	mn = mnt_new_monitor();
+	if (!mn) {
+		warn("failed to allocate monitor");
+		goto err;
+	}
+
+	for (i = 1; i < argc; i++) {
+		if (strcmp(argv[i], "userspace") == 0) {
+			if (mnt_monitor_enable_userspace(mn, TRUE, NULL)) {
+				warn("failed to initialize userspace monitor");
+				goto err;
+			}
+
+		} else if (strcmp(argv[i], "kernel") == 0) {
+			if (mnt_monitor_enable_kernel(mn, TRUE)) {
+				warn("failed to initialize kernel monitor");
+				goto err;
+			}
+		}
+	}
+	if (i == 1) {
+		warnx("No monitor type specified");
+		goto err;
+	}
+
+	return mn;
+err:
+	mnt_unref_monitor(mn);
+	return NULL;
+}
+
+/*
+ * create a monitor and add the monitor fd to epoll
+ */
+static int __test_epoll(struct libmnt_test *ts, int argc, char *argv[], int cleanup)
+{
+	int fd, efd = -1, rc = -1;
+	struct epoll_event ev;
+	struct libmnt_monitor *mn = create_test_monitor(argc, argv);
+
+	if (!mn)
+		return -1;
+
+	fd = mnt_monitor_get_fd(mn);
+	if (fd < 0) {
+		warn("failed to initialize monitor fd");
+		goto done;
+	}
+
+	efd = epoll_create1(EPOLL_CLOEXEC);
+	if (efd < 0) {
+		warn("failed to create epoll");
+		goto done;
+	}
+
+	ev.events = EPOLLIN;
+	ev.data.fd = fd;
+
+	rc = epoll_ctl(efd, EPOLL_CTL_ADD, fd, &ev);
+	if (rc < 0) {
+		warn("failed to add fd to epoll");
+		goto done;
+	}
+
+	printf("waiting for changes...\n");
+	do {
+		const char *filename = NULL;
+		struct epoll_event events[1];
+		int n = epoll_wait(efd, events, 1, -1);
+
+		if (n < 0) {
+			rc = -errno;
+			warn("polling error");
+			goto done;
+		}
+		if (n == 0 || events[0].data.fd != fd)
+			continue;
+
+		printf(" top-level FD active\n");
+		if (cleanup)
+			mnt_monitor_event_cleanup(mn);
+		else {
+			while (mnt_monitor_next_change(mn, &filename, NULL) == 0)
+				printf("  %s: change detected\n", filename);
+		}
+	} while (1);
+
+	rc = 0;
+done:
+	if (efd >= 0)
+		close(efd);
+	mnt_unref_monitor(mn);
+	return rc;
+}
+
+/*
+ * create a monitor and add the monitor fd to epoll
+ */
+static int test_epoll(struct libmnt_test *ts, int argc, char *argv[])
+{
+	return __test_epoll(ts, argc, argv, 0);
+}
+
+static int test_epoll_cleanup(struct libmnt_test *ts, int argc, char *argv[])
+{
+	return __test_epoll(ts, argc, argv, 1);
+}
+
+/*
+ * create a monitor and wait for a change
+ */
+static int test_wait(struct libmnt_test *ts, int argc, char *argv[])
+{
+	const char *filename;
+	struct libmnt_monitor *mn = create_test_monitor(argc, argv);
+
+	if (!mn)
+		return -1;
+
+	printf("waiting for changes...\n");
+	while (mnt_monitor_wait(mn, -1) > 0) {
+		printf("notification detected\n");
+
+		while (mnt_monitor_next_change(mn, &filename, NULL) == 0)
+			printf(" %s: change detected\n", filename);
+
+	}
+	mnt_unref_monitor(mn);
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	struct libmnt_test tss[] = {
+		{ "--epoll", test_epoll, "<userspace kernel ...>  monitor in epoll" },
+		{ "--epoll-clean", test_epoll_cleanup, "<userspace kernel ...>  monitor in epoll and clean events" },
+		{ "--wait",  test_wait,  "<userspace kernel ...>  monitor wait function" },
+		{ NULL }
+	};
+
+	return mnt_run_test(tss, argc, argv);
+}
+
+#endif /* TEST_PROGRAM */