Storage compression patch for Rsync (unfinished)

[Craig Barratt]

> Is there any reason why caching programs would need to set the
> value, rather than it just being a fixed value?
> I think it is hard to describe what this is for and what it should be
> set to.  Maybe a --fixed-checksum-seed option would make some sense,
> or for a caching mechanism to be built in to rsync if it is shown to
> be very valuable.

A fixed value would be perfectly ok; the same magic value that batch
mode uses (32761) would make sense.

> I know people have proposed some caching mechanisms in the past and
> they've been rejected for one reason or another.

One difficulty is that additional files, or new file formats, are needed
for storing the checksums, and that moves rsync further away from its
core purpose.

> I don't think I'll include the option in 2.5.6.

If I submitted a new patch with --fixed-checksum-seed, would you be
willing to at least add it to the patches directory for 2.5.6?

I will be adding block and file checksum caching to BackupPC, and
that needs --fixed-checksum-seed.  This will save me from providing
a customized rsync (or rsync patches) as part of BackupPC; I would
much rather tell people to get a vanilla 2.5.6 rsync release and
apply the specific patch that comes with the release.

Craig