[Box Backup] bbackupd - read errors on database files

[Chris Wilson]

Hi Gary and all,

> I already wrote a quick and dirty prototype a while ago for testing 
> purposes, adding MD5s for all files to file attribute stream and to 
> folder checksum algorithm. Given, my machines use the latest CPUs, but 
> the overall backup completion time overhead was only around 10% - 15%. I 
> also tested CRC-32s, but the difference was only in the 5% area, so MD5s 
> are worth it.

Ben, I'd be happy to implement this (especially if Gary can provide his 
quick and dirty code). What do you say, should we have it for the next 
version (post 0.11)? Maybe as an optional feature, off by default? We 
could store the MD5 checksum as an optional extended attribute, so it 
would be backwards compatible, or else have a special magic value of the 
MD5 field (maybe all zeroes) to indicate that no checksum has been stored.

If necessary, we can run the entire bbackupd test suite twice, once with 
MD5 checksums enabled and once with them disabled, to make sure that 
nothing gets broken either way. Otherwise, I can just write a test that 
uses utimes().

>> I think the consensus is that inode change notification is the most 
>> efficient way to detect changed files. Now we just have to implement 
>> it.
>
> How would that work under Window$?

Windows has the same functionality, but with a different interface. We can 
abstract that out.

Cheers, Chris.
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