Netboot

[arming]

I've searched, but I haven't found, a example of a netboot. I want to do a simple bootloader that loads a kernel in protected mode, but I want that loads the system in a network. How much more difficult to do than a "normal" boot? Any example?

[ACcurrent]

THIS IS A PROJECT THAT IS FAR FROM SIMPLE!
PXELINUX is a sister project to syslinux. Poke your nose around its huge source code. First of, you have to write NIC drivers. Then your screwed, if you aren't then you have to start supporting TCP/IP, DHCP and all that network *. If you aren't dead by now, congrats. OK some info on PXE (wikipedia is always good )
http://en.wikipedia.org/wiki/Preboot_Ex ... nvironment
http://www.lmgtfy.com/?q=pxe

p.s. PLZ dont do it in python

[arming]

THIS IS A PROJECT THAT IS FAR FROM SIMPLE!
PXELINUX is a sister project to syslinux. Poke your nose around its huge source code. First of, you have to write NIC drivers. Then your screwed, if you aren't then you have to start supporting TCP/IP, DHCP and all that network *. If you aren't dead by now, congrats. OK some info on PXE (wikipedia is always good )
http://en.wikipedia.org/wiki/Preboot_Ex ... nvironment
http://www.lmgtfy.com/?q=pxe

p.s. PLZ dont do it in python

thanks, I'll check it. And not, I am not going to do it in Python (basically because I don't know how to programmate in Python )

[arming]

and the source code?

[Brendan]

Hi,

I've searched, but I haven't found, a example of a netboot. I want to do a simple bootloader that loads a kernel in protected mode, but I want that loads the system in a network. How much more difficult to do than a "normal" boot? Any example?

It's relatively easy. Compared to using the BIOS to boot from disk; there's a little extra messing about getting the PXE API entry point and some other details (getting a few networking details from a "cached DHCP packet" structure), but after that you use the PXE API to open files and read from files in real mode, instead of using the BIOS functions and reading sectors in real mode. As a bonus, your boot loader isn't limited to 512 bytes either (e.g. it can be 321 KiB if you want).

Note: If you need to use protected mode, then you'll probably want a wrapper to switch back to real mode, call the PXE API, then return to protected mode; so that you can use the wrapper from protected mode.

Here's some source code for one of my (older) PXE boot loaders: http://bcos.hopto.org/www2/80x86/sys_sr ... x_asm.html

This source code is NASM and runs in real mode (it uses "unreal mode" to copy file data above 0x00100000); but the parts that deal with PXE should be easy enough to understand, especially if you have the PXE specification to use as a reference.

The biggest problem with PXE is that different vendors interpret the specification a little differently; and it can take a little trial and error before you find a way that works for all network card ROMs.

First of, you have to write NIC drivers.

No you don't. The firmware provides them, and also handles DHCP for you. TCP/IP isn't needed at all - TFTP is a very simple protocol (intended to be simple enough for tiny embedded systems) that uses UDP. The firmware handles UDP and TFTP for you too. The firmware has to do all of this to download your boot loader via. TFTP, so there's no point re-implementing any of it in the boot loader itself (rather than just reusing the PXE API that must've worked if your code started at all).


Cheers,

Brendan

[Nessphoro]

p.s. PLZ dont do it in python

This should be a new OSDev meme

[arming]

Thanks!

[shikhin]

Thanks!

There's also a page on PXE on the wiki. Hope it helps.

Regards,
Shikhin