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Comment by ilovecaching | Hacker News Reader

Are there are Darwin hackers lurking on HN? I would pay good money to get a brief summary of the kernel for kernel hackers such as myself who only know how things work in Linux. What are the big architectural differences or cool features not in Linux? Also, how hard is it to upstream changes/get drivers in mainline?

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Amit Singh’s excellent book MacOS Internals: A Systems Approach [1] is a bit outdated now but still recommended if you’re interested in the workings of a non-Linux commercial OS.

[1] https://www.amazon.com/Mac-OS-Internals-Approach-paperback/d...

Jonathan Levin's *OS Internals volumes are an updated version of the same info, and wonderful.

Looks interesting and would love to read/review it. But at $88 a piece for 3 volumes ... hmm!

Volume 1 and 3 are easily worth their money, and then some. (Still waiting for my order of Vol. 2 even though it should have been released a few weeks ago.)

Here's a link to the first volume, made available on the book's website:

http://newosxbook.com/MOXiI.pdf

The Design and Implementation of the FreeBSD Operating System, 2nd ed., in the same category.

https://www.amazon.com/dp/0321968972

Not a Darwin hacker, but:

> What are the big architectural differences or cool features not in Linux?

Darwin is based on XNU from NeXT, which itself is comprised of OSFMK Mach microkernel but with many of the things pulled into the kernel itself for performance. A lot of the stuff with Mach tasks/ports/messages is still there.

> Also, how hard is it to upstream changes/get drivers in mainline?

You can write your own using IOKit but they're not going to be in the mainline tree, because Apple.

> Darwin is based on XNU from NeXT, which itself is comprised of OSFMK Mach microkernel but with many of the things pulled into the kernel itself for performance.

And amusingly, the syscall interface from FreeBSD 4 or so.

IOKit is actually a considerable chunk of the kernel, particularly if you count the various "families", some of which remain open source. I'd say it's Apple's main contribution to the kernel at the architectural level. It's implemented unlike anything in BSD or Linux, as it uses C++ on the kernel side. (The user space side, IOKitUser, is written in C.) These days even Apple uses it for non-device-related kernel services - you can see what the iokit registry looks like on your system using the "ioreg" command or the IORegistryExplorer or IOJones GUI tools.

Darwin is actually a BSD variant, so it does tend to absorb some features from the rest of the bsds such as dtrace. Darwin is nigh-impossible to get patches into as an outsider ( I vaguely remember a blog post or maybe a talk about the process). The rest of the BSDs are fairly easy to get patches into upstream/mainline.

FreeBSD got dtrace in 2009 (FreeBSD 7.1). Mac OS X 10.5 already had dtrace in 2007.

That's because dtrace is a Sun thing, and there was a brief period where Apple and Sun were planning on some very serious collaboration. There was also talk of replacing HFS+ with ZFS at the time.

Darwin is not a thing. It's just Apple dumping the code to satisfy the licensing requirements.

Except it's BSD licensed and not necessary to share the code.

True. But Darwin is still not a thing :) There is no real community, bug tracker, etc. My point that it's just an Apple code dump remains valid, I think.

Open source doesn't necessarily mean open development. Companies like Apple embrace the former without the latter. It is perfectly valid to share your source code openly but not allow outsiders to do development. On a lesser scale, SQLite is another example of open source without allowing open development. You can't really contribute code to SQLite even if you wanted to. Do you think SQLite is not a thing? Heck, even RMS used to be super protective of Emacs.

I did not say it was not open source. I said it's just a code dump, and so far you have not really proved me wrong.

There is not even a proper repository with version history, as far as I can tell. Just this stuff: https://github.com/apple/darwin-xnu/commits/master

That's literally a code dump.

Apple has in the past provided a fully bootable Darwin operating system -- no Gui, but the OS worked just fine.

Your argument is pedantic where pedantry isn't warranted or necessary -- Darwin is a BSD and is BSD licensed, Apple doesn't have to share anything, but they do.

I'm not saying they have to do anything. I'm just wondering why people on this thread are pretending it's anything except a code dump. Look at the Github mirror I've given above. All the commit messages are like this:

  Imported from https://opensource.apple.com/tarballs/xnu/xnu-4903.221.2.tar.gz

I mean, this is a response to an article that illustrates the severe limitations of Darwin as an operating system.

In the area of kernel development, maybe, but Apple develops WebKit, Swift and some other projects in the open.

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