replace_block_direct
replace_block_direct(fs, p, i, newblk);
replace_block_direct(fs, p, V7FS_NADDR_INDEX1, newblk);
replace_block_direct(fs, p, V7FS_NADDR_INDEX2, newblk);
replace_block_direct(fs, p, V7FS_NADDR_INDEX3, newblk);