On Tue, Sep 5, 2023 at 5:15 AM Paul Ruizendaal <
pnr@planet.nl> wrote:
> Does that answer the prompt? Should I try to make this into more of a retrospective paper and actually
> do the research on the areas I was hand-wavy about?
That certainly answered the prompt, much appreciated the walkthrough. Currently just trying to get a view of the field and to collect recollections on how it was done back in the day.
Part of it is finding a conceptual framework that can make sense of it all.
Yes. V7 and other early unix had a 'stand alone' framework. So that's one piece of the puzzle. It could be used for anything (I've seen private diagnostic stand alone programs at Solbourne that would do more extensive tests than the boot roms did for RMA and manufacturing line acceptance). But as they come down to us from AT&T, they are just the bits needed to install a system from scratch (or in some cases fix a system by booting the distribution tapes).
One pitfall I would like to avoid in my own thinking is conflating “installing” and “booting”, even though the two seem related (one loads bits into permanent storage, the other into volatile storage; both are built around incrementally adding capability). When variable hardware comes into play, the two mix even more. Also related is the topic of recovery.
There's "booting" and then there's "bootstrapping". booting happens all the time, but installation happens rarely. The problem is that the install process for V7 and earlier systems was to load a series of programs into memory from tape that did each step of the process to stay within the 64k limits imposed by the platform. That process was done by a series of standalone programs that could, in some cases, act as system repair for certain cases of 'afu' system.
The starting point seems to be a setup where a small set of standalone programs is used to load or repair the bits, as was done for 16-bit unix.
Yea, that's where stand came from originally: An environment that could run a limited program w/o booting the kernel...
A next conceptual step seems to be where first a very basic system is installed that is then used for further installation or for repair. This step seems to have come early, if this 32V install page is reflective of how it was done back in 1980: https://gunkies.org/wiki/Installing_32V_on_SIMH The idea to use disk swap space for this also seems to have come early (and I suppose the concept lives on in “rescue partitions”).
Yes. It was quite common for the next step to be when demand paging became a thing. Once demand paging became a thing and you didn't need a dedicated swap partition, you could 'borrow' the installed system's swap partition (or what would become the installed system's swap partition) to have a richer set of tools. This would use otherwise wasted space for the install, then you'd overwrite it with whatever workload you put on your system.
Another conceptual step might be where early installer phases run a different, smaller kernel (or even OS) than the one being installed. There seems to be much potential for a “wheel of reincarnation” here where as an installer grows large, a pre-installer is created to load the installer and then the pre-installer grows large, etc. For booting, this wheel seems to have turned about 5 times in current Linux. Installing that from scratch on a fully blank SBC (without prepping a removable disk on another computer) also appears to have 4 or 5 revolutions. That is one revolution every 5 years for the 25 years from the late seventies to the early 2000’s.
Indeed, the whole linuxboot saga where you boot a minimal linux kernel that has a shell script (or similar) that decides where to load the complete kernel from is also interesting (doubly so to me because it means I can sneak in at that point and load FreeBSD onto the system).
Then there is the question of where in the "installer stack" to stop. My current interest excludes (precursors to) package managers, containers, etc.
Yes. For me, the 'preboot environment' is a better mental framework to look at it with. Or 'pre-kernel' or 'non-kernel' environments. Though that paradigm runs out of steam in the 90s when people started booting kernels with bundled ram disks (in various flavors) to do the installation to allow boot medium to be used to load additional data (eg the system). The read/write nature of RAM made this vector useful, even when CDROMs appeared on the scene. It was easier to run off a ram disk than off the CDROM because you don't have to have symlinks to a (small) RAM disks for the bits of the system that needed to be read/write during the install process...
The 'standalone' stuff, as typified by the src/stand directory, was all pre-kernel or non-kernel use-cases. Sometimes it was used to build a bit of code that had to be small, but was also used to build code to load the kernel (even dating back to the original boot loader for V7, though I'm relying on my memory which may be confusing that with the 2BSD bootstrap)... The stuff that was 'standalone-but-on-a-unix-kernel' came later.
It might also be amusing to note: I once contemplated porting V7 unix to replace FreeBSD's stand environment to replace the various ad-hock hacks that had grown up. But I found that those hacks were smaller in the end, and needed less code space to support more things (excluding crypto and compression) than the V7 did once you started looking at modifying it to support multiple filesystem types, adding a network stack etc. While V7 is nice and clean, it's also immature in terms of features needed for a modern loader...
Warner
In short: much to ponder, thanks to all for sharing recollections.
> On 4 Sep 2023, at 19:07, Warner Losh <imp@bsdimp.com> wrote:
>
>
>
> On Mon, Sep 4, 2023 at 3:58 AM Paul Ruizendaal via TUHS <tuhs@tuhs.org> wrote:
>
> Recently, I was looking into the “Das U-Boot” boot loader package. Summarised with great simplification, u-boot bundles device drivers, file systems, commands and a Bourne-like shell into a standalone package. Normally it auto-runs a script that brings up a system, but when used in interactive mode it allows a great deal of poking around.
>
> It made me think of the “standalone” set of programs for installing early Unix. On 16-bit understandably each basic command has to be a separate standalone program, but after the shift to 32-bit bundling more functionality in a single binary would have become possible.
>
> How did the Unix “standalone” package evolve in the 80’s, both in the research and BSD lineages? Is there any retrospective paper about that? Or is it a case of “Use the source, Luke”?
>
> The stand package continued in research and BSD to be those programs needed to install and/or recover
> badly damaged systems. You could create a new file system, copy a file from the tape to a partition, etc.
> You couldn't do general scripting with this, by and large.
>
> Originally, they were tape programs. This made sense because of its original focus. In time, some systems
> could load the stand alone programs instead of the kernel, but they continued the original focus.
>
> This is, imho, due in large part due to the miniroot. The miniroot evolved into both a full-enough system
> to do the installation scripts in shell instead of C (Venix, at least, had their install program written in C).
> You'd copy the minroot to swap and then install the system. But a number of additional programs were
> placed into the miniroot so you could do some limited filesystem repair, file editing, etc.
>
> In addition, many vendor's ROMs grew in complexity. Solbourne's ROMs, for example, could do basic
> repair of UFS (clri level, not fsck level), and copy files from one place to another. I often recovered a
> Solbourne system I screwed up by attaching an external SCSI drive that had a known good kernel,
> init, etc.
>
> The 'stand' environment was a whole set of tools that could be used to build stand-alone programs that
> shared much code of their full unix brethren, despite not having a full kernel under them. Kernel services
> were provided by different libraries that did filesystem things, block driver things, network things, etc
> in a similar way to Unix, but with a much reduced footprint.
>
> initramfs, as has been mentioned elsewhere, is pretty much a Linux invention. It was designed to
> 'punt' on the choose where to load things from and have a very minimal interface between the boot
> loader and the system. In time, it grew to support more interfaces, more ways of loading, and better
> ways to mount something that you could then 'pivot' onto. Few other unix systems went this route, though
> many adopted some variation on the pivot_root functionality. Linux has moved beyond the pivot root after
> having booted the correct kernel into being able to take over the machine early in, say, UEFI startup with
> a minimal kernel and initramfs that just knows how to load the next kernel. They skipped the complex boot
> loader stage, and went straight to the 'run linux earlier' stage which is how things like LinuxBoot, coreboot
> and others have put the boot logic into bash scripts. The ability to 'kexec' a kernel and replace the current
> running kernel originated in the 'non-stop' world that wanted to reduce downtime. Now, it's used to reduce
> firmware complexity by eliminating large swaths of UEFI from the boot process, but also generalizes in
> the embedded space.
>
> FreeBSD, from around FreeBSD 2 (1995 or so), had /rescue which largely took over form the stand alone environment
> for the repair duties of things. FreeBSD also adopted a more complex boot loader that would load the
> kernel, modules, set tunables, etc prior to kicking off the kernel. Between /rescue having all the tools needed
> to repair bad updates, repair failing disks, get that one last backup before the drive is dead while you wait
> for the new drive to be delivered, etc, and /boot/loader being able to script loading the kernel while the BIOS
> was still around so the need for drivers in the loader was lessened. However, as the BIOS evolved into UEFI
> and FreeBSD pushed into the embedded space whose firmware provided a less rich environment to the boot
> loader, so it was able to load things off fewer and fewer devices, it became clear that it would need a pivot
> root feature to allow it to boot all the way into FreeBSD, load some drivers from an included ram disk, and then
> use that mount a new root and then 'reroot' to that by killing everything and running init from that new root.
> FreeBSD also moved from Forth to Lua in its scripting language for the boot loader, giving 'pre boot'
> environment support better features. I also added the ability to use FreeBSD boot loader as a Linux binary
> to load FreeBSD and its metadata from a LinuxBoot environment. Finally, FreeBSD has 'spun out' and
> generalized the /rescue feature to allow creation of any 'BeastyBox' environment, similar to what you get
> in a busy box, or clone, environment. This environment, though, is meant in large part on both Linux and
> FreeBSD to be in constrained environments where a full install is prohibitive (even those that never pivot
> to something more, like ap, routers and nas boxes).
>
> NetBSD retains many of the old BSD stand-alone programs that started on the vax. I've not studied things
> beyond noticing this. OpenBSD is similar. Their boot chain is a bit simpler than FreeBSD's, though there's
> noises about porting FreeBSD's boot there. There's a port of /boot/loader to illumos too, but I don't know
> if it is the default, or just available. So I'll not chat about it more.
>
> So the original 'standalone' environment where you had one program running on a system has evolved
> into either a rich boot loader environment that lets one do a lot to decide what kernel to load, or towards
> having a minimal selection of unix programs faster and using /bin/sh or similar to do scripting. These
> reduced environments are often called standalone, though all they share just the name with the earlier
> 'stand' programs: they are full unix programs, but with reduced feature sets and 'linker magic' to package
> them in a way that's faster, smaller, etc (eg all in one binary). FreeBSD's boot loader is an outgrowth
> of the original standalone env, by way of a port of NetBSD's libsa.
>
> I suspect in the future, we'll see more and more of a trend for low-level init and then handing off to some
> built-in kernel (be it Linux, BSD-based (there's now kexec), or whatever) to reuse more of the vetted code
> rather than re-inventing Unix inside the boot loader (which is a valid criticism of FreeBSD's boot loader,
> though it's rich feature set is what you get for the complexity).
>
> Does that answer the prompt? Should I try to make this into more of a retrospective paper and actually
> do the research on the areas I was hand-wavy about?
>
> Warner