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From: Andrew Schulman <andrex AT alumni DOT utexas DOT net>
Subject: Re: problems with overloading of the semantics of version number in cygwin/unison
Date: Thu, 6 Jan 2005 14:22:58 -0500
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> Max Bowsher wrote:
> 
> > Richard Lethin wrote:
> > 
> >> Max Bowsher wrote:
> >>
> >>> Richard Lethin wrote:
> >>>
> >>>> There is a problem with the way that cygwin is updating the version
> >>>> numbers for cygwin/unison.  Unison is used to synchronize filesystems;
> >>>> it can cross different operating systems over IP.  The protocol uses 
> >>>> the
> >>>> version number to decide whether two processes on different systems 
> >>>> will
> >>>> communicate.  2.9.1 is the official released version.  There is a beta
> >>>> version 2.10.2, but it is not widely deployed.  Thus people (like me)
> >>>> will want to use the 2.9.1 version of cygwin's unison.  However, cygwin
> >>>> is numbering its instance of this version 2.9.20-1.  When you try to
> >>>> communicate using cygwin's 2.9.20-1 with a standard 2.9.1 version of
> >>>> unison running on another system, the communication fails after the
> >>>> handshake when it discovers that the cygwin version is "2.9.2 [sic]".
> >>>> Yes, I think that the handshake is truncating the protocol string.
> >>>>
> >>>> Anyway, my suggestion is that cygwin update the version of 2.9.1 
> >>>> that it
> >>>> is distributing, to separate the overloaded concept of version number
> >>>> into a cygwin version number (which could then be arbitrary) and leave
> >>>> the protocol number at 2.9.1
> >>>
> >>>
> >>>
> >>> No, this is nothing to do with cygwin, and everything to do with
> >>> unnecessary inflexibility in the version checking of unison.
> >>>
> >>> It would be a very bad thing for Cygwin to distribute a version of
> >>> unison which lies about which version it is to the other end of the
> >>> connection.
> >>
> >>
> >> Sure, it's a bad design choice in unison, but cygwin is using the
> >> version number in Unison - which means something about the protocol
> >> version in unison - to mean something about the software release - which
> >> operationally is not what unison really means.  The result is that
> >> cygwin unison is broken.
> > 
> > 
> > Unison itself uses the same version number for protocol of software 
> > release.
> > That is a problem if you cannot obtain unison binaries for all machines 
> > you wish to synchronize between from a single source.
> > Nothing in this problem is in any way cygwin specific.
> 
> Where does the version number 2.9.20-1 come from?

Internally, Unison's version number is 2.9.20.  In the Cygwin 
distribution, that package is numbered 2.9.20-1 because it's the first 
release of Unison 2.9.20 in Cygwin.  If I were to apply some bug fixes 
or other changes and release a new version of 2.9.20, it would show up 
in the Cygwin mirrors as 2.9.20-2.  But Unison would still tell you that 
you were using version 2.9.20.

HTH,
A.


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