Replacing 9loadD1135075961Auriel (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#