Date: Mon, 12 Nov 2001 15:08:37 -0800 (PST)
From: John Baldwin <jhb@FreeBSD.org>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: freebsd-arch@FreeBSD.ORG, Robert Watson <rwatson@FreeBSD.ORG>, Terry Lambert <tlambert2@mindspring.com>
Subject: Re: cur{thread/proc}, or not.
Message-ID: <XFMail.011112150837.jhb@FreeBSD.org>
In-Reply-To: <200111122254.fACMsNd06845@apollo.backplane.com>
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On 12-Nov-01 Matthew Dillon wrote: >: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. Yep. They use a mutex for the refcount for now, but I still have patches that some people don't like for implementing a simple refcount API just using atomic operations. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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