[PATCH 09/17] fsinfo: Provide notification overrun handling support [ver #20]

@@ -93,6 +93,8 @@ void notify_mount(struct mount *trigger,
 	n.watch.info	= info_flags | watch_sizeof(n);
 	n.triggered_on	= trigger->mnt_id;
 
+	smp_wmb(); /* See fsinfo_generic_mount_info(). */
+
 	switch (subtype) {
 	case NOTIFY_MOUNT_EXPIRY:
 	case NOTIFY_MOUNT_READONLY:

@@ -4282,6 +4282,17 @@ int fsinfo_generic_mount_info(struct path *path, struct fsinfo_context *ctx)
 	p->mnt_unique_id	= m->mnt_unique_id;
 	p->mnt_id		= m->mnt_id;
 
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+	p->mnt_subtree_notifications = atomic_read(&m->mnt_subtree_notifications);
+	p->mnt_topology_changes	= atomic_read(&m->mnt_topology_changes);
+	p->mnt_attr_changes	= atomic_read(&m->mnt_attr_changes);
+#endif
+
+	/* Record the counters before reading the attributes as we're not
+	 * holding a lock.  Paired with a write barrier in notify_mount().
+	 */
+	smp_rmb();
+
 	flags = READ_ONCE(m->mnt.mnt_flags);
 	if (flags & MNT_READONLY)
 		p->attr |= MOUNT_ATTR_RDONLY;

@@ -4319,6 +4330,9 @@ int fsinfo_generic_mount_topology(struct path *path, struct fsinfo_context *ctx)
 
 	m = real_mount(path->mnt);
 
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+	p->mnt_topology_changes	= atomic_read(&m->mnt_topology_changes);
+#endif
 	p->parent_id = m->mnt_parent->mnt_id;
 
 	if (path->mnt == root.mnt) {

@@ -4445,6 +4459,13 @@ static void fsinfo_store_mount(struct fsinfo_context *ctx, const struct mount *p
 	record.mnt_unique_id	= p->mnt_unique_id;
 	record.mnt_id		= p->mnt_id;
 	record.parent_id	= is_root ? p->mnt_id : p->mnt_parent->mnt_id;
+
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+	record.mnt_notify_sum	= (atomic_read(&p->mnt_attr_changes) +
+				   atomic_read(&p->mnt_topology_changes) +
+				   atomic_read(&p->mnt_subtree_notifications));
+#endif
+
 	memcpy(ctx->buffer + usage, &record, sizeof(record));
 }
 

@@ -100,6 +100,10 @@ struct fsinfo_mount_info {
 	__u64	mnt_unique_id;		/* Kernel-lifetime unique mount ID */
 	__u32	mnt_id;			/* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
 	__u32	attr;			/* MOUNT_ATTR_* flags */
+	__u32	mnt_attr_changes;	/* Number of attribute changes to this mount. */
+	__u32	mnt_topology_changes;	/* Number of topology changes to this mount. */
+	__u32	mnt_subtree_notifications; /* Number of notifications in mount subtree */
+	__u32	padding[1];
 };
 
 #define FSINFO_ATTR_MOUNT_INFO__STRUCT struct fsinfo_mount_info

@@ -113,6 +117,7 @@ struct fsinfo_mount_topology {
 	__u32	dependent_source_id;	/* Dependent: source mount group ID */
 	__u32	dependent_clone_of_id;	/* Dependent: ID of mount this was cloned from */
 	__u32	propagation_type;	/* MOUNT_PROPAGATION_* type */
+	__u32	mnt_topology_changes;	/* Number of topology changes to this mount. */
 };
 
 #define FSINFO_ATTR_MOUNT_TOPOLOGY__STRUCT struct fsinfo_mount_topology

@@ -125,6 +130,9 @@ struct fsinfo_mount_child {
 	__u64	mnt_unique_id;		/* Kernel-lifetime unique mount ID */
 	__u32	mnt_id;			/* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
 	__u32	parent_id;		/* Parent mount identifier */
+	__u32	mnt_notify_sum;		/* Sum of mnt_attr_changes, mnt_topology_changes and
+					 * mnt_subtree_notifications.
+					 */
 };
 
 #define FSINFO_ATTR_MOUNT_CHILDREN__STRUCT struct fsinfo_mount_child

@@ -304,6 +304,8 @@ static void dump_fsinfo_generic_mount_info(void *reply, unsigned int size)
 	printf("\tmnt_uniq: %llx\n", (unsigned long long)r->mnt_unique_id);
 	printf("\tmnt_id  : %x\n", r->mnt_id);
 	printf("\tattr    : %x\n", r->attr);
+	printf("\tmnt_nfy : attr=%u topology=%u subtree=%u\n",
+	       r->mnt_attr_changes, r->mnt_topology_changes, r->mnt_subtree_notifications);
 }
 
 static void dump_fsinfo_generic_mount_topology(void *reply, unsigned int size)

@@ -332,6 +334,7 @@ static void dump_fsinfo_generic_mount_topology(void *reply, unsigned int size)
 		break;
 	}
 
+	printf("\tmnt_nfy : topology=%u\n", r->mnt_topology_changes);
 }
 
 static void dump_fsinfo_generic_mount_children(void *reply, unsigned int size)

@@ -354,8 +357,9 @@ static void dump_fsinfo_generic_mount_children(void *reply, unsigned int size)
 		mp = "<this>";
 	}
 
-	printf("%8x %16llx %s\n",
-	       r->mnt_id, (unsigned long long)r->mnt_unique_id, mp);
+	printf("%8x %16llx %10u %s\n",
+	       r->mnt_id, (unsigned long long)r->mnt_unique_id,
+	       r->mnt_notify_sum, mp);
 }
 
 static void dump_string(void *reply, unsigned int size)