[Virtual-linux-support] How It All Works

[Scott F. <sfr...@ho...>]

Hi Everyone! (Mårten especially!)

I have been following this project since the release of VL10devrelease1.iso

I have to say, that I have found this project to very interesting. I have 
also
seen other CDROM based distribution like knoppix 
(http://www.knopper.net/knoppix)
that can boot from cdrom into a stand alone Linux environment. However, this 
project's
approach is much closer to a REAL Linux install.

Now, onto what I started to write ... How It All Works.

In a nut shell the filesystem is abstracted into two parts; the static 
files, and the dynamic files. The static files are stored on the cdrom in a 
compressed loopback file (cloop) mounted in the root of the ramdisk. The 
dynamic files are in the initrd that get loaded at boot time and stored in 
the ramdisk (ram0). Additionally, files saved to disk during previous runs 
are loaded into the ramdisk over writing what was loaded by the initrd. In 
addition to the dynamic files, there are symbolic links that point to every 
static file in the .virtual_root folder. The system is essentially a 
standard Mandrake install except for some small parts in the startup and 
shutdown. Here is what I have been able to determine;

(please correct me or fill in where I'm wrong or missing something)

OPERATION:

->power
->bios
  ->cdrom boot
   ->isolinux (see isolinux.cfg)
    ->load Linux kernel (vmlinux)
    ->load initrd		(initrd.gz)
    [KERNEL STARTS - with initrd.gz loaded into ram0 as root]
      ->/bin/init (init 3 or init 5 from the isolinux.cfg. 3 being multiuser 
and 5 being x11)
       ->/etc/rc.d/rc.sysinit
        ->/bin/findcd
         (umount /initrd)
         (compress ramdisk)(new ... nice!)
         (make /.virtual_root directory)
         (mount /proc)
         (load scsi module)
         (loops through cdrom drives looking for virtual Linux cdrom)
         [CDROM FOUND]
          (load cloop kernel driver (pointing to found iso.compressed image)
          (mount cloop (device) image to /.virtual_root)
          (mount devfs)
          (mount devpts)
          (exit (return) to rc.sysinit)
         [CDROM NOT FOUND]
          (bombs out waiting for user to reboot)
        [VARIOUS OTHER INIT STUFF] (setting clock, keymap, ect.)
        ->/bin/vlutil swap
         (creates a list of known swap partitions and dumps them into 
/etc/fstab)
         (turns swap on)
         (exit (return) to rc.sysinit)
        [FSCK removed]
        [MTAB clear removed]
        [VARIOUS OTHER INIT STUFF] (setting hdparam, modules, devfsd.)
        ->/bin/vlutil locate
         (creates a list of known hard disk)
         (tries to mount all known hard disk and puts links onto 
/root/Desktop/...)
         (exit (return) to rc.sysinit)
        ->/bin/vlutil settings
         [checks /proc/cmdline for clean=]
          (if yes, clear the virt_linux folder off hard disk)
          (if no, load saved files over-writing initrd)(root.tgz, etc.tgz, 
update.tgz, etc.)
           (exit (return) to rc.sysinit)
        [VARIOUS OTHER INIT STUFF] (/etc/init.d/mandrake_everytime, etc.)
      [init level 3 (multiuser) or 5 (X11) called by init](see isolinux.cfg)

	[** SYSTEM IS UP AND RUNNING **]

	[LOGIN](root account)
	 ->.bashrc
        (checks to see if /etc/.configure is present)
        (if yes -> normal login)
        (if no -> runs drakeconf in a loop until user cancels -> then normal 
login)

	[SHUTDOWN REQUESTED (init 6)]
	->/bin/init 6
	->/etc/rc.d/init.d/halt
	 [VARIOUS OTHER INIT STUFF]
	 ->/bin/vlutil umount
	  saves /etc & /root as tar gzip archives to the virt_linux folder
        unmounts all mounted filesystems
      [** SYSTEM REBOOTS **]


FILES REFERENCED:

/etc/rc.d/rc.sysinit	(modified)
/etc/rc.d/init.d/halt	(modified)
/bin/findcd			(added)
/bin/vlutil			(added)
/etc/.configure		(used)
$vfat/virtual_root	(added, used for storage & settings)


QUESTIONS:

A few questions I have are;

1) Does the cdrom really need to have the (initrd?) filesystem present. If 
the files are being
loaded from the initrd.gz and the virt_linux/*.tgz files, why are they also 
present on the root of the cdrom?

2) Is there a linuxrc step missing, or is this a leftover from previous 
versions? (in the isolinux.cfg it refers to init=/linuxrc)

3) Are there any other files, packages, and etc. that have been modified for 
this project?
   (anything not noticeable from the surface?)

Scott Franzyshen


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