On 2013-05-08, at 9:51, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > You have > calculated = jbd2_chksum(j, calculated, buf, j->j_blocksize); > provided = be32_to_cpu(tag->t_checksum); > > return provided == cpu_to_be32(calculated); > > in there, which makes no sense whatsoever. First of all, you are > converting big-endian to native, then another native to big-endian > and compare results. The bogosity aside, it's equivalent to simply > comparing tag->t_checksum with calculated - cpu_to_be32() is the > same mapping as be32_to_cpu() on all architectures and it's a one-to-one > mapping, at that. I agree this is a bit of extra swabbing that isn't needed. > Bogosity, of course, is that tag->t_checksum is apparently big-endian > and definitely a 16bit value. How in hell is that check going to > yield true? Note that you are asking for 16 bits out of crc32c result > to be zero, _NOT_ to be ignored. I think you're mixing up the jbd2 transaction block checksum, which actually has up to 128 bits of space (in case we want to move to a better checksum in the future) with the ext4 group descriptor checksum (which is only 16 bits for compatibility reasons). Problem solved? Cheers, Andreas > Producer of that value shoves lower 16 bits of cpu_to_be32(crc) into the > on-disk structure. Also a bloody bad idea, since the values on little-endian > and big-endian hosts will be different; move the disk from one box to > another and watch the mismatches... > > What the hell is going on there? > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
