util-linux/0074-libmount-ignore-unwanted-kernel-events-in-monitor.patch

From e8de2e75d712dd9a750bde130b4367546b46a0bd Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Mon, 22 Jan 2024 13:04:44 +0100
Subject: libmount: ignore unwanted kernel events in monitor

If the mount operation requires multiple steps, it's optimal for the
libmount monitor to ignore the steps until we get a complete mount
(reported by the utab.event file).

This commit adds a new API function, mnt_monitor_veil_kernel(), to
ignore unwanted kernel mount events.

Note that this only makes sense when the application monitors kernel
and userspace events simultaneously.

Addresses: https://issues.redhat.com/browse/RHEL-14612
Upstream: http://github.com/util-linux/util-linux/commit/a2b5a4e0adf9543843bb0aef94d21e7105cf8159
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 libmount/docs/libmount-sections.txt |  1 +
 libmount/src/libmount.h.in          |  2 ++
 libmount/src/libmount.sym           |  1 +
 libmount/src/monitor.c              | 55 ++++++++++++++++++++++++++---
 4 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/libmount/docs/libmount-sections.txt b/libmount/docs/libmount-sections.txt
index d9263b8ad..43bb80f1c 100644
--- a/libmount/docs/libmount-sections.txt
+++ b/libmount/docs/libmount-sections.txt
@@ -449,5 +449,6 @@ mnt_monitor_get_fd
 mnt_monitor_close_fd
 mnt_monitor_next_change
 mnt_monitor_event_cleanup
+mnt_monitor_veil_kernel
 mnt_monitor_wait
 </SECTION>
diff --git a/libmount/src/libmount.h.in b/libmount/src/libmount.h.in
index a51ac1ea5..b57b6bcd6 100644
--- a/libmount/src/libmount.h.in
+++ b/libmount/src/libmount.h.in
@@ -671,6 +671,8 @@ extern int mnt_monitor_enable_kernel(struct libmnt_monitor *mn, int enable);
 extern int mnt_monitor_enable_userspace(struct libmnt_monitor *mn,
 				int enable, const char *filename);
 
+extern int mnt_monitor_veil_kernel(struct libmnt_monitor *mn, int enable);
+
 extern int mnt_monitor_get_fd(struct libmnt_monitor *mn);
 extern int mnt_monitor_close_fd(struct libmnt_monitor *mn);
 extern int mnt_monitor_wait(struct libmnt_monitor *mn, int timeout);
diff --git a/libmount/src/libmount.sym b/libmount/src/libmount.sym
index 88bce5c4b..13071b9cd 100644
--- a/libmount/src/libmount.sym
+++ b/libmount/src/libmount.sym
@@ -368,4 +368,5 @@ MOUNT_2_37 {
 MOUNT_2_40 {
 	mnt_ref_lock;
 	mnt_unref_lock;
+	mnt_monitor_veil_kernel;
 } MOUNT_2_37;
diff --git a/libmount/src/monitor.c b/libmount/src/monitor.c
index 040a5ee11..b5cc7e768 100644
--- a/libmount/src/monitor.c
+++ b/libmount/src/monitor.c
@@ -64,6 +64,8 @@ struct libmnt_monitor {
 	int			fd;		/* public monitor file descriptor */
 
 	struct list_head	ents;
+
+	unsigned int		kernel_veiled: 1;
 };
 
 struct monitor_opers {
@@ -469,12 +471,28 @@ err:
 	return rc;
 }
 
+static int kernel_event_verify(struct libmnt_monitor *mn,
+			       struct monitor_entry *me)
+{
+	int status = 1;
+
+	if (!mn || !me || me->fd < 0)
+		return 0;
+
+	if (mn->kernel_veiled && access(MNT_PATH_UTAB ".act", F_OK) == 0) {
+		status = 0;
+		DBG(MONITOR, ul_debugobj(mn, "kernel event veiled"));
+	}
+	return status;
+}
+
 /*
  * kernel monitor operations
  */
 static const struct monitor_opers kernel_opers = {
 	.op_get_fd		= kernel_monitor_get_fd,
 	.op_close_fd		= kernel_monitor_close_fd,
+	.op_event_verify	= kernel_event_verify
 };
 
 /**
@@ -543,6 +561,28 @@ err:
 	return rc;
 }
 
+/**
+ * mnt_monitor_veil_kernel:
+ * @mn: monitor instance
+ * @enable: 1 or 0
+ *
+ * Force monitor to ignore kernel events if the same mount/umount operation
+ * will generate an userspace event later. The kernel-only mount operation will
+ * be not affected.
+ *
+ * Return: 0 on success and <0 on error.
+ *
+ * Since: 2.40
+ */
+int mnt_monitor_veil_kernel(struct libmnt_monitor *mn, int enable)
+{
+	if (!mn)
+		return -EINVAL;
+
+	mn->kernel_veiled = enable ? 1 : 0;
+	return 0;
+}
+
 /*
  * Add/Remove monitor entry to/from monitor epoll.
  */
@@ -850,6 +890,8 @@ static struct libmnt_monitor *create_test_monitor(int argc, char *argv[])
 				warn("failed to initialize kernel monitor");
 				goto err;
 			}
+		} else if (strcmp(argv[i], "veil") == 0) {
+			mnt_monitor_veil_kernel(mn, 1);
 		}
 	}
 	if (i == 1) {
@@ -896,12 +938,14 @@ static int __test_epoll(struct libmnt_test *ts, int argc, char *argv[], int clea
 		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);
+		int n;
+
+		printf("waiting for changes...\n");
 
+		n = epoll_wait(efd, events, 1, -1);
 		if (n < 0) {
 			rc = -errno;
 			warn("polling error");
@@ -958,6 +1002,7 @@ static int test_wait(struct libmnt_test *ts, int argc, char *argv[])
 		while (mnt_monitor_next_change(mn, &filename, NULL) == 0)
 			printf(" %s: change detected\n", filename);
 
+		printf("waiting for changes...\n");
 	}
 	mnt_unref_monitor(mn);
 	return 0;
@@ -966,9 +1011,9 @@ static int test_wait(struct libmnt_test *ts, int argc, char *argv[])
 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" },
+		{ "--epoll", test_epoll, "<userspace kernel veil ...>  monitor in epoll" },
+		{ "--epoll-clean", test_epoll_cleanup, "<userspace kernel veil ...>  monitor in epoll and clean events" },
+		{ "--wait",  test_wait,  "<userspace kernel veil ...>  monitor wait function" },
 		{ NULL }
 	};
 
-- 
2.43.0