Replacing 9load
D1135075961
Auriel (82.182.149.46)
#! Date: Mon, 5 Dec 2005 15:47:14 -0500
#! From: Russ Cox <rsc@swtch.com>
#! To: 9fans <9fans@cse.psu.edu>
#! Subject: [9fans] replacing 9load
#
#For quite a few years, various of us have talked about replacing
#9load. When Jim and I replaced b.com with the combination of ld.com
#and 9load, we considered using a stock Plan 9 kernel instead. Sean
#Quinlan took a few steps toward making this possible: he added the
#configuration environment #ec, the Dev.shutdown routines, and
#/dev/reboot. With these, one can use the kernel as an impromptu boot
#loader already. I believe Ron Minnich does just that in some of his
#machines.
#
#There are a few things 9load does that the kernel depends on. The
#main one is loading plan9.ini from somewhere and leaving it in
#memory. A secondary one is setting up the APM BIOS interface, and in
#the original VESA code written for Inferno, 9load was responsible
#for setting up the VGA. With the new realmode code (or better, if
#someone would write it, VM86 code) in the kernel, the APM and VESA
#can be done by the kernel proper. That leaves plan9.ini.
#
#Plan9.ini serves two related but different purposes. The first is to
#give the kernel hints about hardware recognition. The second is to
#specify a few aspects of the software configuration. Ideally, it
#would be nice if plan9.ini could become optional.
#
#Hardware recognition was a much bigger problem in the old ISA days.
#Plan9.ini was, at the time, an excellent alternative to recompiling
#the kernel to hard-wire all the constants about your machine. Now
#that we have PCI and its device ids, you don't need to tell the
#kernel what hardware you have anymore. It knows, usually better than
#you.
#
#That leaves the software configuration: mouse, vga, serial console,
#kernel location, root file system location, boot menu, etc. The
#mouse and vga could possibly be auto-detected, and the new vga
#resize code (if it works) makes it possible to correct a bad guess
#about the user's desired screen size.
#
#The other options in plan9.ini -- the serial console, the kernel and
#root file system, the boot menu -- can't just be guessed. Jim has
#been playing with loading plan9.ini via PXE/TFTP, which is great for
#a real single-file-server Plan 9 setup, though it won't satisfy the
#single-machine users. I don't expect this part of plan9.ini to go
#away, though one could make 9load do without it in the general case
#(scan the local 9fats for files named 9pc*, for example).
#
#When I put the new mmu code into the kernels, I didn't feel like
#putting it into 9load too. Instead I wrote a small binary that turns
#a gzipped kernel into a 9load binary that the PBS bootstrap could
#load into memory. You run
#
#! cat load 9pcload.gz >9load
#
#to produce a 9load from a kernel. I have put this in
#/n/sources/contrib/rsc/load.
#
#This new program means that you can build yourself a special pcload
#kernel with some 9load-like user-level program installed as
#/boot/boot instead of the usual boot. It would find plan9.ini,
#present any prompts if needed, find and load a kernel, and then
#/dev/reboot into it. You could put dossrv, ext2srv, fossil, venti,
#kfs, factotum, mount, tftp, ftpfs, hget, etc., into the root file
#system, to load kernels off of any conceivable medium.
#
#While a new 9load using the real kernel could be great, it's not
#very high on my or Jim's to do list, since the current 9load
#suffices, and we're more interested in what happens once the kernel
#is in memory than the mundane and now all-too-familiar details of
#the x86 boot process.
#
#I encourage those of you grumbling for a new 9load to attack one of
#the following problems:
#
# *	write vm86 code for the kernel to replace the realmode code. vm86
#	code should be safer and more reliable and will make the vesa and
#	apm code run on more machines.
#
# *	write a mouse auto-detector: scan the usb, try ps2, scan the
#	serial ports. this should be almost trivial.
#
# *	write a vga size auto-detector: try aux/vga -m vesa -p and fetch
#	and parse the edid information from the monitor. aux/vga does most
#	of this already.
#
# *	write a user-level program to be the `9load' in a 9pcload kernel.
#	the program should have generic "get me a plan9.ini" and "get me a
#	kernel" interfaces, like the current 9load, so that many boot
#	methods can be plugged in.
#
#Ironically, once this is all done we'll have moved full circle to
#where Plan 9 was many years ago, when the hobbit boot loader was
#just a Plan 9 kernel with a different load address and a special
#boot program that let you set environment variables, examine memory,
#attach to file servers, run programs that were downloaded, and load
#and boot a kernel.
#
#Russ
#