[syslinux] Returning to syslinux bootloader

[Dag Wieers]

On Thu, 16 Apr 2009, Jeffrey Hutzelman wrote:

> --On Thursday, April 16, 2009 02:39:35 PM +0200 Dag Wieers <dag at wieers.com> 
> wrote:
>
>>  I was wondering whether it is technically possible to go back from eg.
>>  DOS or Linux directly to the bootloader (instead of rebooting the
>>  hardware).
>>
>>  We currently have 2 images (one DOS and one Linux) that need to be
>>  started before loading a system. They do things like disable PXE on NICs
>>  (using an Intel DOS tool), verify the correctness of the network
>>  patchings and validate if the hardware was configured according to
>>  corporate standards (usage of PCI slots, hardware revisions and firmware).
>
> Generally, no.  As Peter points out, tools like HDT actually run with the 
> bootloader still in memory, while DOS and Linux expect to take over the 
> machine.  However, there are some games you might be able to play to chain 
> from one to another...
>
> Boot the DOS system first, do what you need to do to reprogram the NIC, then 
> use LOADLIN to load the Linux image.  Once your Linux image has done what it 
> needs to do, use kexec to load the kernel and initrd for the real system 
> installer.
>
> This assumes that the installer itself is Linux based, so you're booting
> PXELINUX -> MEMDISK -> DOS -> Linux -> Linux.  The files you need for DOS, 
> including LOADLIN and the kernel and initrd for the first Linux, all live in 
> a FAT filesystem in a ramdisk provided by MEMDISK.  The kernel and initrd for 
> the second Linux live inside the initrd for the first.
>
> Of course, if you're booting from media instead of via PXE, then you can just 
> use SYSLINUX and a local FAT filesystem instead of PXELINUX and MEMDISK.  The 
> concept is the same.

Yes, this is what I planned to do. Although my first goal is to get rid of 
DOS altogether. I don't understand why vendors still provide DOS hardware 
config utilities, while it is much easier to automate something via Linux.

It is pretty ugly to send the correct boot-options (eg. anaconda network 
info and boot-options) that I have in syslinux (on a per system basis) via 
DOS to loadlin. It also requires me to have all the different 
kernels/initrds in DOS, while they are now available only from isolinux. 
(I guess a generic DOS CD driver would work though).

All-in-all being able to save some state somewhere in syslinux would be 
very useful so that I know after each reboot what we have to do next. I 
was thinking if we have lua scripting, we could use the VPD to store some 
information and make the process less interactive.

Then I could do:

  - first reboot
      store phase 1 somewhere in VPD
      ask for system name (and store in VPD)

      store phase 2 somewhere in VPD
      hardware configuration changes (DOS)

  - second reboot
      store phase 3 somewhere in VPD
      load network debugging tool (Linux)

  - third reboot
      store phase 4 somewhere in VPD
      load the system with required OS (RHEL/ESX)

Now each of these tasks require someone to type something, and wait for 
reboots (which on some systems can take up 2 to 3 minutes).

-- 
--   dag wieers,  dag at wieers.com,  http://dag.wieers.com/   --
[Any errors in spelling, tact or fact are transmission errors]