problems with overloading of the semantics of version number in cygwin/unison

Richard Lethin
Thu Jan 6 19:36:00 GMT 2005

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?

> Cygwin unison works without problems with other copies of cygwin unison,

and this is only marginally useful.

> and any other platform's unison of the same version.

Right, but who else uses the version number of 2.9.20-1?

> Max.

Richard Lethin
Reservoir Labs, Inc.
+1-212-780-0527 ext. 102

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