Changing the hash in S3?

[Volker Lendecke]

On Thu, Jun 16, 2011 at 02:15:25PM +0930, Rusty Russell wrote:
> On Wed, 15 Jun 2011 22:05:13 -0400, simo <idra at samba.org> wrote:
> > On Thu, 2011-06-16 at 11:15 +0930, Rusty Russell wrote:
> > > As part of my cleanups wrt TDB2, I've switched several places from using
> > > TDB1's tdb_jenkins_hash to CCAN's hash_any function (where TDB's came from).
> > > 
> > > The difference is that the CCAN version varies with endian; the TDB one
> > > is always little endian (with an associated penalty on big endian
> > > machines).
> > > 
> > > Jeremy, Volker, does it matter?  If these hashes are supposed to be
> > > stable on disk across upgrades, I'll switch it to hash_stable() (which
> > > is *exactly* the same hash as tdb_jenkins_hash).
> > 
> > It does matter, we always tried to have a compatible disk format so that
> > tdb (and ldb) files can be easily moved from a big endian machine and
> > analyzed on a little endian one.
> 
> Yes, but are these hashes placed into a TDB?
> 
> For example:
> 
> commit 831ff4519e5e30752cab814a5d06008942a1fd58
> Author: Volker Lendecke <vl at samba.org>
> Date:   Tue Mar 15 09:30:22 2011 +0100
> 
>     s3: Use jenkins hash for str_checksum, fix bug 8010
> 
> This makes no mention of compatibility problems, so I assume changing it
> again is fine?
> 
> How about these, which added an entirely new hash field?
> 
> commit 76418e23bcde1eba4dfefbc10c51c083567a52e6
> Author: Jeremy Allison <jra at samba.org>
> Date:   Tue Jan 25 13:49:01 2011 -0800
> 
>     Add name_hash to files_struct. Set within fsp_set_smb_fname().
> 
> commit b97f1ce68a512cb0da71ee1de9ddaa49dd466068
> Author: Jeremy Allison <jra at samba.org>
> Date:   Tue Jan 25 14:01:52 2011 -0800
> 
>     Add name_hash into the share mode entry struct (as yet only use for renames to identify a specific path).

Probably those are fine. They will break rolling code
upgrade in a cluster though, something that is often asked
for but what we never promised.

Volker

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