On Wed, May 08, 2013 at 10:04:31AM -0600, Andreas Dilger wrote: > 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. Yes, that is effing awful. It looks like I missed that detail at some point, probably when tweaking the endian handling or something. > 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). The journal block tag checksum is 16 bits long. > Problem solved? I wish. Now we know what I'll be patching today... Anyhow, thank you for catching this. --D > > 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 -- 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
