fsnotify: lazy attach fsnotify_sb_info state to sb

Define a container struct fsnotify_sb_info to hold per-sb state,
including the reference to sb marks connector.

Allocate the fsnotify_sb_info state before attaching connector to any
object on the sb and free it only when killing sb.

This state is going to be used for storing per priority watched objects
counters.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240317184154.1200192-8-amir73il@gmail.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 83004d9e07a3..c9f2b2f6b493 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -477,6 +477,23 @@ struct fsnotify_mark_connector {
 	struct hlist_head list;
 };
 
+/*
+ * Container for per-sb fsnotify state (sb marks and more).
+ * Attached lazily on first marked object on the sb and freed when killing sb.
+ */
+struct fsnotify_sb_info {
+	struct fsnotify_mark_connector __rcu *sb_marks;
+};
+
+static inline struct fsnotify_sb_info *fsnotify_sb_info(struct super_block *sb)
+{
+#ifdef CONFIG_FSNOTIFY
+	return READ_ONCE(sb->s_fsnotify_info);
+#else
+	return NULL;
+#endif
+}
+
 static inline atomic_long_t *fsnotify_sb_watched_objects(struct super_block *sb)
 {
 	return &sb->s_fsnotify_connectors;