On Tue, Feb 10, 2004 at 09:56:00PM -0800, Craig Barratt wrote: > On Mon, Feb 09, 2004 at 09:14:06AM -0500, Jason M. Felice wrote: > > > I got the go-ahead from the client on my --link-by-hash proposal, and > > the seed is making the hash unstable. I can't figure out why the seed > > is there so I don't know whether to cirumvent it in my particular case > > or calculate a separate, stable hash. > > I believe the checksum seed is meant to reduce the chance that different > data could repeatedly produce the same md4 digest over multiple runs. > If a collision happens the hope is that a different checksum seed will > break the collision. > > However, my guess is that it doesn't make any difference. Certainly > adding the seed at the end of the block won't change a collision even > if the seed changes over multiple runs. File MD4 checksums add the > seed at the beginning, which might help breaking collisions, although > I'm not sure. > > Wayne Davison writes: > > > There was some talk last year about adding a --fixed-checksum-seed > > option, but no consensus was reached. It shouldn't hurt to make the > > seed value constant for certain applications, though, so you can feel > > free to proceed in that direction for what you're doing for your client. > > > > FYI, I just checked in some changes to the checksum_seed code that will > > make it easier to have other options (besides the batch ones) specify > > that a constant seed value is needed. > > I would really like a --fixed-csumseed option become a standard > feature in rsync. Just using the batch value (32761) is fine. > Can I contribute a patch? The reason I want this is the next > release of BackupPC will support rsync checksum caching, so that > backups don't need to recompute block or file checksums. This > requires a fixed checksum seed on the remote rsync, hence the > need for --fixed-csumseed. I've included this feature in a > pre-built rsync for cygwin that I include on the SourceForge > BackupPC downloads.
1. Yes, you may contribute a patch. I favor the idea of being able to supply a checksum seed. 2. Lets get the option name down to a more reasonable length. --checksum-seed should be sufficient. -- ________________________________________________________________ J.W. Schultz Pegasystems Technologies email address: [EMAIL PROTECTED] Remember Cernan and Schmitt -- To unsubscribe or change options: http://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html