BLKPTR_PER_INDIR
nbppindir *= BLKPTR_PER_INDIR;
blkid = (c->dataoff / c->datablksz) / BLKPTR_PER_INDIR;
iblkid = blkid & (BLKPTR_PER_INDIR - 1);
for (size_t i = 0; i < BLKPTR_PER_INDIR; i++)
blkid /= BLKPTR_PER_INDIR;
if (blkid % BLKPTR_PER_INDIR != 0)
blkid /= BLKPTR_PER_INDIR;
l1id = (off / c->datablksz) & (BLKPTR_PER_INDIR - 1);