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Apple’s Darwin OS and XNU Kernel Deep Dive

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Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#71

Post by comex »

krackers wrote: post #67
comex wrote: post #54

Earlier quoted context omitted.

The claim is inaccurate and mixes together multiple different things: - The Mach microkernel originally supported true userland paging, like mmap but with an arbitrary daemon in place of the filesystem. You can see the interface here: https://web.mit.edu/darwin/src/modules/xnu/osfmk/man/memory_... But I'm not sure if Darwin ever used this functionality; it certainly hasn't used it for the last ~20 years. - dynamic_pa…

>xnu could alert it when it was low on swap; dynamic_pager would create swap files, and pass them back into the kernel What's the benefit of this indirection through userspace for swap file creation? Can't the kernel create the swap file itself?

Today the kernel does create the swap file itself. I don't know why it behaved differently in the past, given that the version of dynamic_pager I linked is only 355 lines of code, not obviously complex enough to be worth offloading to userspace. But this was written back in 1999 and maybe there was more enthusiasm for being microkernel-y (even if they had already backed away from full Mach paging).

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#72

Post by comex »

larusso wrote: post #63

I’m not sure if I/O kit was written in this c++ subset just for speed. There was this controversial at the time. Apple announced MacOS X and said that it won’t be compatible with current software. All partners would need to rewrite the software in Objective-C. This didn’t go over well. Apple back paddelt and introduced “carbon”. An API layer for cpp applications as well as “Core Foundation” an underpinning to the obj…

IOKit C++ is running in the kernel, so it's not really related to any of the technologies you mentioned which are all userland-only.

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#73

Post by laurencerowe »

GianFabien wrote: post #22
swatson741 wrote: post #8

Whenever I see the Darwin kernel brought into the discussion I can't help but wonder how different things could have been if Apple had just forked Linux and ran their OS services on top of that. Especially when I think about how committed they are to Darwin it really paints a poor image in my mind. The loss that open source suffers from that, and the time and money Apple has to dedicate to this with a disproportionat…

Back in the days when Apple acquired NeXT, Linux was undergoing lots of development and wasn't well established. Linux being a monolithic kernel didn't offer the levels of compartmentalization that Mach did. As things now stand, FreeBSD represents many of the benefits of Darwin and the open source nature of Linux. If you seek a more secure environment without Apple's increasing levels of lock-in, then FreeBSD (and th…

Isn’t FreeBSD a monolithic kernel? I don’t believe it provides the compartmentalisation that you talk about.

As I understand it Mach was based on BSD and was effectively a hybrid with much of the existing BSD kernel running as a single big task under the microkernel. Darwin has since updated the BSD kernel under microkernel with the current developments from FreeBSD.

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#74

Post by TickleSteve »

laurencerowe wrote: post #73
GianFabien wrote: post #22

Earlier quoted context omitted.

Back in the days when Apple acquired NeXT, Linux was undergoing lots of development and wasn't well established. Linux being a monolithic kernel didn't offer the levels of compartmentalization that Mach did. As things now stand, FreeBSD represents many of the benefits of Darwin and the open source nature of Linux. If you seek a more secure environment without Apple's increasing levels of lock-in, then FreeBSD (and th…

Isn’t FreeBSD a monolithic kernel? I don’t believe it provides the compartmentalisation that you talk about. As I understand it Mach was based on BSD and was effectively a hybrid with much of the existing BSD kernel running as a single big task under the microkernel. Darwin has since updated the BSD kernel under microkernel with the current developments from FreeBSD.

Mach was never based on BSD, it replaced it. Mach is the descendant of the Accent and Aleph kernels. BSD came into the frame for the userland tools.

"Mach was developed as a replacement for the kernel in the BSD version of Unix," (https://en.wikipedia.org/wiki/Mach_(kernel))

Interestingly, MkLinux was the same type of project but for Linux instead of BSD (i.e. Linux userland with Mach kernel).

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#77

Post by [deleted] »

monocasa wrote: post #70
lunarlull wrote: post #38

Earlier quoted context omitted.

Making a switch is one thing, but using Linux from the start for OS X would have made more sense. The only reason that didn't happen is because of Jobs' attachment to his other baby. It wasn't a bad choice, but it was a choice made from vanity and ego over technical merit.

AFAICT Linux wasn't even ported to PowerPC at the time of NextSTEP being acquired by Apple.

[deleted]

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#78

Post by kalleboo »

threeseed wrote: post #57
linguae wrote: post #24

Earlier quoted context omitted.

Interestingly enough, Apple did contribute to porting Linux to PowerPC Macs in the mid-1990s under the MkLinux project, which started in 1996 before Apple’s purchase of NeXT later that year: https://en.m.wikipedia.org/wiki/MkLinux I don’t think there was any work done on bringing the Macintosh GUI and application ecosystem to Linux. However, until the purchase of NeXT, Apple already had the Macintosh environment runn…

Completely forget about MkLinux. The timing is fascinating. MkLinux was released in February 1996 whilst Copland got officially cancelled in August 1996. So it's definitely conceivable that internally they were considering to just give up on the Copland microkernel and run it all on Linux. And maybe this was a legitimate third option to BeOS and NeXT that was never made public.

What's crazy is that MkLinux was actually Linux-on-Mach, not just a baremetal PowerPC Linux. The work they did to port Mach to PowerPC for MkLinux was then reused in the port of NeXTSTEP Mach to PowerPC. Everything was very intertwined.

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#79

Post by johndoe0815 »

monocasa wrote: post #70
lunarlull wrote: post #38

Earlier quoted context omitted.

Making a switch is one thing, but using Linux from the start for OS X would have made more sense. The only reason that didn't happen is because of Jobs' attachment to his other baby. It wasn't a bad choice, but it was a choice made from vanity and ego over technical merit.

AFAICT Linux wasn't even ported to PowerPC at the time of NextSTEP being acquired by Apple.

Apple was firstly involved in porting Linux to PPC, albeit running on top of Mach 3 in MkLinux, since early 1996:

https://en.m.wikipedia.org/wiki/MkLinux

Re: Apple’s Darwin OS and XNU Kernel Deep Dive

#80

Post by inkyoto »

GianFabien wrote: post #22
swatson741 wrote: post #8

Whenever I see the Darwin kernel brought into the discussion I can't help but wonder how different things could have been if Apple had just forked Linux and ran their OS services on top of that. Especially when I think about how committed they are to Darwin it really paints a poor image in my mind. The loss that open source suffers from that, and the time and money Apple has to dedicate to this with a disproportionat…

Back in the days when Apple acquired NeXT, Linux was undergoing lots of development and wasn't well established. Linux being a monolithic kernel didn't offer the levels of compartmentalization that Mach did. As things now stand, FreeBSD represents many of the benefits of Darwin and the open source nature of Linux. If you seek a more secure environment without Apple's increasing levels of lock-in, then FreeBSD (and th…

> As things now stand, FreeBSD represents many of the benefits of Darwin and the open source nature of Linux.

No. FreeBSD has committed the original sin of UNIX by deliberately dropping support for all non-Intel architectures, intending to focus on optimising FreeBSD for the Intel ISA and platforms. UNIX portability and support for a diverse range of CPU's and hardware platforms are ingrained in the DNA of UNIX, however.

I would argue that FreeBSD has paid the price for this decision – FreeBSD has faded into irrelevance today (despite having introduced some of the most outstanding and brilliant innovations in UNIX kernel design) – because the FreeBSD core team bet heavily on Intel remaining the only hardware platform in existence, and they missed the turn (ARM, RISC-V, and marginally MIPS in embdedded). Linux stepped in and filled in the niche very quickly, and it now runs everywhere. FreeBSD is faster but Linux is better.

And it does not matter that Netflix still runs FreeBSD on its servers serving up the content at the theoretical speed of light – it is a sad living proof of FreeBSD having become a niche within a niche.

P.S. I would also argue that the BSD core teams (Free/Net/Open) were a major factor in the downfall of all BSD's, due to their insular nature and, especially in the early days, a near-hostile attitude towards outsiders. «Customers» voted with their feet – and chose Linux.

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