From owner-freebsd-net  Mon Oct  7 23: 7:17 2002
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Date: Mon, 7 Oct 2002 23:06:24 -0700 (PDT)
From: Don Lewis <dl-freebsd@catspoiler.org>
Subject: Re: CFR: m_tag patch
To: nate@root.org
Cc: julian@elischer.org, tlambert2@mindspring.com, sam@errno.com,
	freebsd-arch@FreeBSD.ORG, freebsd-net@FreeBSD.ORG
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On  7 Oct, Nate Lawson wrote:
> On Mon, 7 Oct 2002, Julian Elischer wrote:

>> it is just working on the principal that there is not going to be 
>> a collision in the 32 bit space. Especially when we create them from
>> "time since the epoch", and when teh various authors can see each
>> other's choices of value.
> 
> There are deterministic ways to generate them.
> 1. A counter -- gettag() { return tag++; }
> 2. A LCRG -- gettag() { return (A * tag) % n; }
> 3. A global registry -- "Hey, gimme a major"
> 
> There are non-deterministic ways as well, i.e. hash functions and
> PRNGs.  And if code can run faster than a given time source, the output of
> that source or permutation thereof can produce collisions.
> 
> What leads you towards the time-based option vs. the others, especially
> the deterministic ones?

Why not name them?  At boot or module load time stuff the name in a
table and use the table index as the 16 bit ID.  Is there any reason the
ID has to be the same each time the system is booted?


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