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Re: Booting El Torito image from a partition table


From: Emilio Lazo Zaia
Subject: Re: Booting El Torito image from a partition table
Date: Sat, 28 Nov 2015 14:04:09 -0430
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:42.0) Gecko/20100101 Icedove/42.0


On 28/11/15 13:50, Andrei Borzenkov wrote:
28.11.2015 21:16, Emilio Lazo Zaia пишет:
On 28/11/15 13:31, Andrei Borzenkov wrote:
28.11.2015 19:55, Emilio Lazo Zaia пишет:
Of course isohdppx.bin code and isohybrid binary are ISOLINUX specific,
so we can't combine
them with GRUB2. The problem here seems to be that GRUB2 boot_hybrid.img
don't pass
partition information to core.img because it wasn't designed to handle
partitioned devices. Right?

The problem is that boot_hybrid.img does not know about partition
information that is passed to it by syslinux using method specific to
syslinux.

The only syslinux code in my example is mbr.bin that is a generic MBR
binary code to boot from the
first partition which has the bootable flag. In those steps we can avoid
writing syslinux's mbr.bin into
/dev/loop0 and using install-mbr binary, which isn't related to syslinux
and provides the same
functionality, coded in a different way.

How MBR is related to your case? Quoting your first mail: "using
chain.c32 module I can chainload into another partition's boot sector"

If you look at chain code, it passes the same information using the same
method (partition entry pointed to by %SI register).
I'm sorry; I think my first mail wasn't clear because I tried to explain the whole context.

In such disk there are more than one iso9660 partitions, so there is also some syslinux menu to select which one we want to boot to; that's why chain.c32. In the second mail I isolated the situation to one partition and an MBR code that boots into it, so no syslinux menu and no syslinux code is present, except for the mbr.bin that can be replaced with install-mbr being the behavior the same.






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