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Date:      Wed, 7 Feb 2001 15:35:57 -0500 (EST)
From:      Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
To:        des@ofug.org
Subject:   Re: xucred introduction
Message-ID:  <200102072035.PAA46466@khavrinen.lcs.mit.edu>
In-Reply-To: <mit.lcs.mail.freebsd-arch/xzpk872mfjs.fsf@flood.ping.uio.no>
References:  <mit.lcs.mail.freebsd-arch/2863.981571804@critter>

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In article <mit.lcs.mail.freebsd-arch/xzpk872mfjs.fsf@flood.ping.uio.no> you write:
>Some structures (specifically, those that are to be stored in zones)
>*must* start with two pointers to their own type.

No, they don't.

See, e.g., struct inpcb.

The restriction that you get from the zone allocator is that the
beginning of the zone is overlaid with two such pointers *while the
object is free*, so you cannot depend on type-stability for values
which would be stored there.  In the TCP stack, the only thing we
really care about being type-stable is the generation count, which was
intentionally placed at the end of the structure.

-GAWollman

-- 
Garrett A. Wollman   | O Siem / We are all family / O Siem / We're all the same
wollman@lcs.mit.edu  | O Siem / The fires of freedom 
Opinions not those of| Dance in the burning flame
MIT, LCS, CRS, or NSA|                     - Susan Aglukark and Chad Irschick


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