Hi, Sorry to bother you.

Basically, a 128-byte inode inside a filesystem that allocated 256 bytes
for each inode.  As you point out, the old code would checksum the entire
allocated space, whether or not the inode core used it.  Obviously, you
want this since inline extended attributes live in that space:

csum = ext4_chksum(sbi, ei->i_csum_seed, (__u8 *)raw,
                  EXT4_INODE_SIZE(inode->i_sb));

The new code, on the other hand, carefully checksums around the
i_checksum fields and only bothers to checksum the space between the end
of i_checksum_hi and the end of the allocated space if the inode core is
big enough to store i_checksum_hi.  Since we allocated 256 bytes for
each inode, we checksum the first two bytes after byte 128
(EXT4_GOOD_OLD_INODE_SIZE), but then we see that i_extra_size == 0 so we
never bother to checksum anything after that.  This is of course wrong
since we no longer checksum the xattr space and we've deviated from the
pre-4.7.4 (documented) on-disk format.

Oops. I had overlooked the case of that i_extra_size is less than 4.
I misunderstood the previous Darrick's codes calculating inode checksum value.
Sorry about that. :-(
 

if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
       offset = offsetof(struct ext4_inode, i_checksum_hi);
       csum = ext4_chksum(sbi, csum, (__u8 *)raw +
                          EXT4_GOOD_OLD_INODE_SIZE,
                          offset - EXT4_GOOD_OLD_INODE_SIZE);
       if (EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
               csum = ext4_chksum(sbi, csum, (__u8 *)&dummy_csum,
                                  csum_size);
               offset += csum_size;
       }
       csum = ext4_chksum(sbi, csum, (__u8 *)raw + offset,
                          EXT4_INODE_SIZE(inode->i_sb) - offset);
}

Can you give that a try?

Darrick, your modification looks good enough to me.

Thank you, guys.