Messages in this thread | | | From | John Bradford <> | Subject | Re: Bootable CD idea | Date | Wed, 30 Apr 2003 13:41:13 +0100 (BST) |
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> > Just a random idea that occurred to me... > > > > Since the El-Torito bootable CD standard supports multiple floppy > > images on a single CD, it would be possible to write a script that > > takes a .config file, and the source to, say all the -pre and -rc > > versions of a particular kernel, compiles multiple kernels with the > > same .config, and writes a CD with them all on, set to boot from an > > arbitrary disk partition. > > > > It would make: > > > > > > > Foo doesn't work in -rc2 > > > > Did it work in -rc1 > > > Not sure > > > > E-Mail exchanges a thing of the past. > > > > Note, that as each floppy image is separate, it's not the same as > > trying to cram multiple kernels on a 2.88 MB floppy image, and is > > therefore actually do-able :-). > > > > John. > > Well, it's a boot-loader problem that has to be solved in one > of the boot-loader programs like grub or lilo. When booting a > CD, the BIOS is made to 'think' that a CD is a floppy. It > loads the boot-record and jumps to its code. From that point > on, whatever happens is based upon how, what, and where the > boot record and subsequent code executes. With the large > data space available, you could certainly have multiple > operating systems. It's simply a coding problem. If you > want to modify one of the existing boot-loader programs > let me know. I may be able to help, and certainly can test.
I didn't think we'd need to modify anything - the BIOS lets us choose the floppy image we want, so each image only needs to contain a bootloader[1], and a kernel. The root filesystem doesn't need to be on the CD - if the disk is to be used for quickly visiting another kernel to see if something breaks, you'd want your normal root filesystem. If you set the root filesystem to /dev/fd0, you can actually use a real floppy, as the kernel bypasses the BIOS floppy emulation :-). So, you can boot from a CD, and use a floppy that you've prepared separately as your root filesystem.
Were you suggesting that we could have the root filesystem as a set of blocks on the CD, which are accessed directly, and not via El-Torito floppy emulation? That would be pretty useful. Heh, initial ram disk on a CD would be even better...
[1] I originally thought that the 2.4 kernel's in-built floppy bootloader used BIOS calls to access the disk, and that a 2.4 kernel image as the El-Torito boot image would work, as the kernel would be accessing the emulated disk, but it didn't seem to when I tried it just now - it failed with an error saying something along the lines of it had run out of data to decompress.
> FYI I have a bootable CR/ROM (who doesn't), that contains > a limited root file-system with ramdisks that mount on > /tmp and /var. I use this to boot any linux machine and > repair it. It would be nice to be able to select different > operating system versions as well.
Yeah, maybe I was just being lazy, but I imagined something like:
make allprepatches
running the same config through 2.4.21-pre1 to -pre7, and -rc1, and writing a CD that boots and gives you a menu to select from.
Kind of like make bzdisk, but for 2003 instead of 1991 :-).
I mean, if we're killing of the in-kernel bootloader in 2.5, why not?
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