Date: Mon, 12 Nov 2001 14:54:23 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
To: Terry Lambert <tlambert2@mindspring.com>
Cc: Robert Watson <rwatson@FreeBSD.ORG>, freebsd-arch@FreeBSD.ORG
Subject: Re: cur{thread/proc}, or not.
Message-ID: <200111122254.fACMsNd06845@apollo.backplane.com>
References: <Pine.NEB.3.96L.1011111101234.11566A-100000@fledge.watson.org> <3BF05241.74F895EF@mindspring.com>
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:The point is that if the credentials are granted, then a
:change in credential is not a change of the credential itself,
:but is instead a copy-on-write proposition. In other words,
:credentials, once granted, are priviledge stable.
:
:If this is the case, then they are written when they are
:instanced, cloned before they are modified (indeed, it seems
:that the clone/modify operation must be made atomic), and
:thus are never written once instanced -- only destroyed on
:the 1->0 reference transition.
:
:If so, then no locking is required, since the LCK CMPXCHG can
:be utilized to do atomic increment and decrement on the
:reference counting, without needing locks.
:...
:
:-- Terry
Yes, I believe this is how credentials work. I looked at
the code about 6 months ago. We should not have to do any
locking of the credential stuff, only simple mutexing
around the ref counter. That is how it should work
is how I believe it currently works.
-Matt
Matthew Dillon
<dillon@backplane.com>
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