BTRFS_FS_STATE_COUNT
#define STATE_STRING_BUF_LEN (sizeof(STATE_STRING_PREFACE) + BTRFS_FS_STATE_COUNT + 1)
WARN_ON_ONCE(bit >= BTRFS_FS_STATE_COUNT);
if ((bit < BTRFS_FS_STATE_COUNT) && fs_state_chars[bit]) {