Add scoutfs_lock_ino_refresh_gen

Add a lock call to get the current refresh_gen of a held lock.   If the
lock doesn't exist or isn't readable then we return 0.  This an be used
to track lock coverage of structures without the overhead and lifetime
binding of the lock coverage struct.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/lock.c

@@ -1528,6 +1528,38 @@ void scoutfs_lock_flush_invalidate(struct super_block *sb)
 		flush_work(&linfo->inv_work);
 }
 
+static u64 get_held_lock_refresh_gen(struct super_block *sb, struct scoutfs_key *start)
+{
+	DECLARE_LOCK_INFO(sb, linfo);
+	struct scoutfs_lock *lock;
+	u64 refresh_gen = 0;
+
+	/* this can be called from all manner of places */
+	if (!linfo)
+		return 0;
+
+	spin_lock(&linfo->lock);
+	lock = lock_lookup(sb, start, NULL);
+	if (lock) {
+		if (lock_mode_can_read(lock->mode))
+			refresh_gen = lock->refresh_gen;
+	}
+	spin_unlock(&linfo->lock);
+
+	return refresh_gen;
+}
+
+u64 scoutfs_lock_ino_refresh_gen(struct super_block *sb, u64 ino)
+{
+	struct scoutfs_key start;
+
+	scoutfs_key_set_zeros(&start);
+	start.sk_zone = SCOUTFS_FS_ZONE;
+	start.ski_ino = cpu_to_le64(ino & ~(u64)SCOUTFS_LOCK_INODE_GROUP_MASK);
+
+	return get_held_lock_refresh_gen(sb, &start);
+}
+
 /*
  * The caller is going to be shutting down transactions and the client.
  * We need to make sure that locking won't call either after we return.

kmod/src/lock.h

@@ -100,6 +100,8 @@ void scoutfs_lock_del_coverage(struct super_block *sb,
 bool scoutfs_lock_protected(struct scoutfs_lock *lock, struct scoutfs_key *key,
 			    enum scoutfs_lock_mode mode);
 
+u64 scoutfs_lock_ino_refresh_gen(struct super_block *sb, u64 ino);
+
 void scoutfs_free_unused_locks(struct super_block *sb);
 
 int scoutfs_lock_setup(struct super_block *sb);