Re: Booting El Torito image from a partition table

[Emilio Lazo Zaia]

I'm sorry for the lateness of my answer.

On 02/12/15 14:17, Andrei Borzenkov wrote:
> 02.12.2015 08:20, Emilio Lazo Zaia пишет:
> > I did it.
> Congratulations :)
Thank you!
> > Yes, I mean eltorito.img code, which is cdboot.img + core.img
> > concatenated; right? So the code that lacks partition drivers is the
> > core.img part... I've extracted core.img from Kaspersky CD:
> No, you did not :)
I didn't? :-)

But the code in the embedding area is not core.img? in the case of a 
bootable iso9660 image, embedding zone contains cdboot.img with 
core.img, AFAIK.

> > - In Kaspersky CD (kav_rescue_10.iso) I've extracted the boot code +
> > core.img, located at the embedding area, just after the MBR of the
> > hybrid image:
> >
> > # dd if=kav_rescue_10.iso bs=512 skip=1 count=54 of=eltorito.img
> >
> > - Dropped the cdboot.img part:
> >
> > # dd if=eltorito.img bs=2048 skip=1 of=core.img
> Both steps are completely redundant, see below.

I thought I needed the boot binaries (.img files) on KCD to build a 
core.img that match the compilation, and it is wrong... With the usage 
of grub-install you pointed at the very end of your mail works perfectly 
for building a core.img that match the runtime compilation of KCD 
because we are including .mod files from KCD.

> > - I created a helper partition (20MB, on /dev/sdf31) in btrfs and
> > mounted it on /x.
> > - Extracted all contents of kav_rescue_10.iso on my home, cd to
> > boot/grub and copy extracted core.img to i386-pc to be used with
> > grub-install:
> You could simply mount partition.
>
> > # cp [/path/to/extracted/core.img] i386-pc/core.img
> Redundant as well.
>
> > # grub-install /dev/sdf31 --boot-directory=/x -d i386-pc
> grub-install always creates core.img from scratch, so none of previous
> steps was needed.
...And it can take modules from another compilation no matter we are 
generating a boot code with a newer/older GRUB... This generated code is 
compilation-independent, and that's what I didn't know. That's why I've 
extracted the whole core.img from the CD.
> You can also spare jumping through indirection hoops and simply create
> image file that will point directly to your partition, similar to
>
> address@hidden:~$ lsblk
> NAME             MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
> sda                8:0    0 465,8G  0 disk
> ├─sda1             8:1    0   500M  0 part /boot/efi
> ├─sda2             8:2    0    40M  0 part
> ├─sda3             8:3    0     3G  0 part
> ├─sda4             8:4    0 446,5G  0 part /
> └─sda5             8:5    0  15,8G  0 part [SWAP]
> loop0              7:0    0   512M  0 loop
> ├─loop0p1        259:0    0   100M  0 loop
> ├─loop0p2        259:1    0   411M  0 loop
> ├─loop0p1 (dm-0) 252:0    0   100M  0 part /mnt
> └─loop0p2 (dm-1) 252:1    0   411M  0 part /tmp/kasp
> address@hidden:~$ cat /mnt/syslinux.cfg
> label Kaspersky
>         menu Kaspersky
>         com32 chain.c32
>         append file=kaspersky.img
> address@hidden:~$ grub-mkimage -O i386-pc -o /tmp/temp.img -p
> '(,msdos2)/boot/grub' -d /tmp/kasp/boot/grub/i386-pc  biosdisk
> part_msdos iso9660
> address@hidden:~$ cat /tmp/kasp/boot/grub/i386-pc/lnxboot.img
> /tmp/temp.img > /tmp/kaspersky.img
> address@hidden:~$ sudo mv /tmp/kaspersky.img /mnt
>
> Now selecting Kaspersky in syslinux boots directly into partition2.
> Replace "msdos" with "gpt" if needed and adjust partition number.
Indeed, I did include part_gpt and the prefix as '(,gpt20)/boot/grub'... 
The prefix starting with ',' always means the current disk?

The 20MB helper partition becames a 20KB helper file used to boot Kaspersky.

Thank you!!! You helped me a lot.
Emilio.