util-linux/0069-libmount-introduce-run-mount-utab.event.patch

From dfdd500a339804075900bd1af42e433cf8d8f632 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Wed, 3 Jan 2024 14:13:28 +0100
Subject: libmount: introduce /run/mount/utab.event

The mnt_monitor_...() API uses /run/mount/utab.lock to monitor utab
changes. The same file is used to control access to the utab file.

The utab can be updated more than once during one mount(8) call, for
example, one update is done in /sbin/mount.nfs and next in mount(8).
This situation triggers two (e.g. inotify) events when monitoring is
based on the lock file.

It seems better to introduce separate file to trigger the event and do
not trigger this event in /sbin/mount.<type> helpers.

Addresses: https://issues.redhat.com/browse/RHEL-14612
Upstream: http://github.com/util-linux/util-linux/commit/544824929a740ed5f8108c752872c7f082f301cf
References: 477401f0de404aafbc7630f70c2f8b1d670e32f8
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 libmount/src/context.c    |  6 ++++--
 libmount/src/monitor.c    | 16 +++++++---------
 libmount/src/mountP.h     |  1 +
 libmount/src/tab_update.c | 19 +++++++++++++++++++
 4 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/libmount/src/context.c b/libmount/src/context.c
index 71b8d730a..c03b0ea64 100644
--- a/libmount/src/context.c
+++ b/libmount/src/context.c
@@ -2293,7 +2293,7 @@ int mnt_context_update_tabs(struct libmnt_context *cxt)
 
 		if (mnt_update_already_done(cxt->update, cxt->lock)) {
 			DBG(CXT, ul_debugobj(cxt, "don't update: error evaluate or already updated"));
-			goto end;
+			goto emit;
 		}
 	} else if (cxt->helper) {
 		DBG(CXT, ul_debugobj(cxt, "don't update: external helper"));
@@ -2317,7 +2317,9 @@ int mnt_context_update_tabs(struct libmnt_context *cxt)
 				cxt->mountflags & MS_RDONLY);
 
 	rc = mnt_update_table(cxt->update, cxt->lock);
-
+emit:
+	if (rc == 0 && !mnt_context_within_helper(cxt))
+		mnt_update_emit_event(cxt->update);
 end:
 	if (!mnt_context_switch_ns(cxt, ns_old))
 		return -MNT_ERR_NAMESPACE;
diff --git a/libmount/src/monitor.c b/libmount/src/monitor.c
index dada02ed3..4db56c2e0 100644
--- a/libmount/src/monitor.c
+++ b/libmount/src/monitor.c
@@ -224,18 +224,16 @@ static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
 	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.
+	 * libmount uses utab.event file to monitor and control utab updates
 	 */
-	if (asprintf(&filename, "%s.lock", me->path) <= 0) {
+	if (asprintf(&filename, "%s.event", me->path) <= 0) {
 		rc = -errno;
 		goto done;
 	}
 
-	/* try lock file if already exists */
+	/* try event file if already exists */
 	errno = 0;
-	wd = inotify_add_watch(me->fd, filename, IN_CLOSE_NOWRITE);
+	wd = inotify_add_watch(me->fd, filename, IN_CLOSE_WRITE);
 	if (wd >= 0) {
 		DBG(MONITOR, ul_debug(" added inotify watch for %s [fd=%d]", filename, wd));
 		rc = 0;
@@ -254,7 +252,7 @@ static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
 		if (!*filename)
 			break;
 
-		/* try directory where is the lock file */
+		/* try directory where is the event file */
 		errno = 0;
 		wd = inotify_add_watch(me->fd, filename, IN_CREATE|IN_ISDIR);
 		if (wd >= 0) {
@@ -337,10 +335,10 @@ static int userspace_event_verify(struct libmnt_monitor *mn,
 			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)
+			if (e->mask & IN_CLOSE_WRITE)
 				status = 1;
 			else {
-				/* event on lock file */
+				/* add watch for the event file */
 				userspace_add_watch(me, &status, &fd);
 
 				if (fd != e->wd) {
diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index 4b4c5de1e..99b913c99 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -476,6 +476,7 @@ extern int mnt_context_deferred_delete_veritydev(struct libmnt_context *cxt);
 /* tab_update.c */
 extern int mnt_update_set_filename(struct libmnt_update *upd,
 				   const char *filename, int userspace_only);
+extern int mnt_update_emit_event(struct libmnt_update *upd);
 extern int mnt_update_already_done(struct libmnt_update *upd,
 				   struct libmnt_lock *lc);
 
diff --git a/libmount/src/tab_update.c b/libmount/src/tab_update.c
index f60f522ce..5ae369b74 100644
--- a/libmount/src/tab_update.c
+++ b/libmount/src/tab_update.c
@@ -1003,6 +1003,25 @@ done:
 	return rc;
 }
 
+int mnt_update_emit_event(struct libmnt_update *upd)
+{
+	char *filename;
+	int fd;
+
+	if (!upd || !upd->filename)
+		return -EINVAL;
+
+	if (asprintf(&filename, "%s.event", upd->filename) <= 0)
+		return -errno;
+
+	fd = open(filename, O_WRONLY|O_CREAT|O_CLOEXEC,
+			    S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH);
+	free(filename);
+	if (fd < 0)
+		return -errno;
+	close(fd);
+	return 0;
+}
 
 #ifdef TEST_PROGRAM
 
-- 
2.43.0