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Matrix Mole wrote:
>
> How difficult would it be for someone to modify initfs 
> so that it looked onto the CD drive 

It could be done.  initfs is still sitting (unused) in a 
ramdisk when BL3 (DOS version) is running.  You can see
it in the /initrd directory.

The main problem is that the BL3 kernel does not have built-in
CDrom capability.  You need to do three insmods.  So, if initfs
is going to access the CDrom, it will need to include those 
three modules (which means a bigger ramdisk).

> Which would be easier. Recompile the kernel for the larger 
> ramdisk, or to modify the initfs script so that it pulls 
> fs.img off the CD?

Recompiling the kernel would be much easier.  Take the BL3 
config; change one parameter (ramdisk size) and compile.
If you gzip fs.img, you can then use it as the initrd for 
loadlin.exe.
 
> it does let me learn a little bit "second hand" so to speak 
> on how BL systems boot up.  

BL1 and BL2 simply unzipped a compressed filesystem to 
ramdisk and pointed a kernel at it using loadlin.exe.  
There are two disadvantages of that method:  any changes
made by the user disappear when reset and the capacity is 
limited by the size of the ramdisk (which needs to be kept 
small for old PCs).

To eliminate those problems, the DOS version of BL3 uses a 
loop-file.  However, loops are more complicated to set up 
than simple ramdisks.  First you boot a tiny ramdisk to 
create the loop, and then the kernel runs the loop as the 
root filesystem.  

The floppy version of BL3 uses a different method (because
there is no capacity for a large loop-file).  It boots from
LILO (which requires less space than booting DOS and then
loadlin.exe) and unzips the BL3 skeleton into a 4mb ramdisk.
The first thing the skeleton does is load the rest of BL3
(from the second floppy) into a second 4mb ramdisk.  A new
kernel is not required because both ramdisks are standard 
size.

Cheers,
Steven