[dm-devel] Some thoughts about providing data block checksumming for ext4

[Mikulas Patocka]

> > Recovery after a power fail
> > ---------------------------
> > 
> > If the dm-protected device was not cleanly shut down, then we need to
> > examine all of the checksum blocks in the Active Area.  For each
> > checksum block in the AA, the checksums for all of their data blocks
> > should machine either the checksum found in the AA, or the checksum
> > found in the checksum block in the checksum group.
> 
> ... and if the checksum of the block matches BOTH the checksum in the AA 
> and the checksum in the checksum group (because of checksum function 
> collision), you don't know which 4-bit nibble belongs to the data in the 
> block.

Though, I realize that you could avoid this problem by selecting the 
appropriate checksum function - that never results in collision if the 
4-bit nibble differs.

Mikulas