FreeBSD and MacOS

[Q]

On 30/06/2004, at 4:40 PM, Chris Zumbrunn wrote:

>
> On 30. Jun 2004, at 3:01, Alasdair Lumsden wrote:
>
>> While Mach is derived from 4.3BSD (circa 1986~1988), there's been 
>> about
>> 15 years worth of divergence since then. For example, FreeBSD is
>> monolithic while Mach is more micro-kernel based. Also the driver 
>> models
>> are quite different, eg Darwin uses IOKit (Object Oriented driver
>> interface model).
>
> From Apple's webpages previewing Tiger:
>
> "The upgraded kernel, based on FreeBSD 5.x, provides optimised 
> resource locking for better scalability across multiple processors, 
> support for 64-bit memory pointers through the System library and 
> standards-based access control lists."
>
> http://www.apple.com.au/macosx/tiger/unix.html

Some of the newer code in Darwin is "based on FreeBSD 5.x" yes, but the 
monolithic FreeBSD kernel (as a whole) is not one of them. Instead 
apple has targeted the "interesting" bits and imported these pieces of 
the kernel as discrete components into Darwin (they are implemented 
this way anyway).

Darwin still uses a Mach kernel design, although Apple has made some 
significant modifications to its implementation to reduce message 
passing overhead and latency etc, making it something of a hybrid and 
no longer a pure micro-kernel. As a result the Darwin Mach kernel is 
not the traditional Mach mix of userspace/kernelspace RPC connected 
components, instead the kernel is linked into a single address space, 
using kernel extensions (loadable modules) in a similar way FreeBSD 
does.  However these extensions are implemented using a highly object 
oriented API (IOKit) for interacting with the kernel, instead of the 
traditional struct passing procedural approach used in FreeBSD.

The portions of the FreeBSD kernel that Apple have adopted can be found 
as part of the XNU project (the darwin kernel) from Apple's Opensource 
website
http://www.opensource.apple.com/darwinsource/
The CVS tags should still be intact on the files in question.

While FreeBSD provides a sizable chunk of Darwin's BSDness, it still 
has a decent amount of legacy NeXT/BSD code in it as well.

Some of the things that have been adopted from FreeBSD/NetBSD in the 
Darwin kernel include:

Crypto support
Filesystem support for CD9660, DEVFS, NFS, VFS, MEMDEV (Curiously this 
doesn't include UFS/FFS support)
IP & IPV6 TCP stack support including BPF & IPFW
Most of the BSD/Posix/SYSV system calls (sysctl, fork, exec, ktrace, 
mmap, etc) and corresponding MAN pages.

-- 
Seeya...Q

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