un_bol_lof
if (new_lof < ul->un_bol_lof) {
nb = new_lof - ul->un_bol_lof;
inval_range(ul, &ul->un_wrbuf, ul->un_bol_lof, nb);
inval_range(ul, &ul->un_rdbuf, ul->un_bol_lof, nb);
beg_blkno = btodb(ul->un_bol_lof);
ASSERT(new_lof >= ul->un_bol_lof);
beg_blkno = btodb(ul->un_bol_lof);
ident += (bp->b_blkno - btodb(ul->un_bol_lof));
if (ul->un_tail_lof < ul->un_bol_lof)
ul->un_tail_lof = ul->un_bol_lof;
bol = ul->un_bol_lof;
ul->un_tail_lof = ul->un_bol_lof;
dst_lof = ul->un_bol_lof;
ul->un_tail_lof = ul->un_bol_lof;
nfb = (ul->un_head_lof - ul->un_bol_lof) +