xtTruncate_pmap
extern s64 xtTruncate_pmap(tid_t tid, struct inode *ip, s64 committed_size);
new_size = xtTruncate_pmap(tid, new_ip, new_size);
new_size = xtTruncate_pmap(tid, ip, new_size);
return xtTruncate_pmap(tid, ip, 0);