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Date: Mon, 23 Jan 2012 14:03:51 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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Subject: Re: Problem with gethostid
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On Jan 23 10:53, Corinna Vinschen wrote:
> While gethostid is not guaranteed to return a globally unique ID, I
> think I see the potential flaws in the algorithm.  It shouldn't be too
> hard to make it a bit more intelligent.
> 
> Or, we just replace it with a simple algorithm as it's described in the
> glibc man pages.  First it checks if /etc/hostid exists and uses the
> value from there.  If not, it calls gethostname and gethostbyname to
> fetch the (or better "a") IPv4 address and tweaks the bits a bit.

I just simplified the gethostid function in Cygwin.  It now fetches the
registry value HKLM/Software/Microsoft/Cryptography/MachineGuid and
creates a hash value from it.  The MachineGuid is supposed to be
globally unique so there's a low probability for collision, even if the
hostid hash is only 32 bit.

If that's not sufficient, I can also make gethostid depend on /etc/hostid
and the IPv4 address in the first place, as on Linux.  I have the code for
that, but given the uniqueness of the MachineGuid I don't see the point
to make the function more complicated than necessary.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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