From owner-freebsd-net@FreeBSD.ORG  Mon Mar 19 20:23:18 2007
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Date: Mon, 19 Mar 2007 13:23:17 -0700
From: Julian Elischer <julian@elischer.org>
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To: Ignacio Rey <unixero@gmail.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: networking code and splx()
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Ignacio Rey wrote:
> Hello everyone,
> 
> I'm studying a bit the FreeBSD networking code.
> 
> I've read "TCP/IP illustrated vol 2" by G. R. Wright and W. R. Stevens,
> which describes code in 4.4BSD-lite.
> 
> Now I'm taking a look at FreeBSD 6.2 release. Some things are different,
> many others kept the same. What I'm confused about is that in 4.4BSD
> there are many calls to the splx() family of functions, and I didn't see
> any of them in the networking code in FreeBSD. However the 'grep' program
> showed me that they are used in other parts of the kernel.

There was a major change in the way that synchronization was done bewteen FreeBSD 4.x
and FreeBSD 5.X.
The changes were to support real multiprocessor operation and were extensive.
The 'spl" method of operation was only able to protect operation on a single CPU.

You should probably get a copy of "The design of the FreeBSD (um 5.2 I think) 
Operating System by Kirk McKusick and George Neville-Neil.
It goes into some of the changes. (many changes have happenned since then too).
the New locking largely depends on Mutexes.

> 
> 
> The question is: Have calls to these functions been wrapped? or are they
> simply not used in this context?
> 
> 
> Thanks in advance,
> 
> Ignacio
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