lfs_log2
u_int lfs_log2(u_int);
lfs_sb_setbshift(fs, lfs_log2(bsize));
lfs_sb_setffshift(fs, lfs_log2(fsize));
lfs_sb_setfbshift(fs, lfs_log2(lfs_sb_getfrag(fs)));
segshift = lfs_log2(ssize);
lfs_sb_setblktodb(fs, lfs_log2(db_per_blk));
lfs_sb_setfsbtodb(fs, lfs_log2(fsize / secsize));
lfs_sb_setsushift(fs, lfs_log2(lfs_sb_getsepb(fs)));