>>> Atomic commit. The superblock, which references the updated
>>> version of the filesystem, carries a sequence number and a
>>> checksum. It is written to one of two alternating locations. On
>>> restart, both locations are read and the highest numbered
>>> superblock with a correct checksum is chosen as the new
>>> filesystem root.
>> Yes... and which ever part of the superblock contains the sequence
>> number must be written atomically.
> The only requirement here is that the checksum be correct. And sure,
> that's not a hard guarantee because, on average, you will get a good
> checksum for bad data once every 4 billion power events that mess up
> the final superblock transfer. Let me see, if that happens once a year,
In a tree-structured filesystem, checksums on everything would only
cost you space similar to the number of pointers you have. Whenever
a non-leaf node points to a child, it can hold a checksum for that
child as well.
This gives a very reliable way to spot filesystem errors, including
corrupt data blocks.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to email@example.com
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/