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Date: Tue, 8 Jul 2014 19:47:51 +0400
From: Andrey Borzenkov <arvidjaar@gmail.com>
To: The development of GNU GRUB <grub-devel@gnu.org>
Subject: Re: Chainloadig from grub2 to isolinux
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В Tue, 8 Jul 2014 16:39:41 +0300
"Raif S. Berent" <rsb@berentweb.com> пишет:

> Not to beat a dead horse, but I'd like to clarify a few issues that
> seem to be not working.
> 
> 1. I compiled and installed Grub_trunk on an old laptop, then copied
> the debian.iso to a folder under (hd0,gpt*). Modified the grub.cfg and
> tried to use "syslinux_configfile -i (loop)/isolinux/isolinux.cfg -r
> (loop)" I got the exact same result as PXE booting (No CD-ROM). From
> what I can tell, debian needs the loopback module from the iso loaded
> and the iso to be loop-mounted as a second device in order to get this
> working (have not asked the debian folk).
> 
> 2. Most Debian-based iso's fail to properly boot with loopback over
> PXE, including the likes of GParted and Inquisitor. They mostly fail
> with kernel panic: can't mount root.
> 

If I understand correctly, you expect linux to be able to access grub
(loop) device. That's not going to work. Once grub loads linux and
transfers control to it, (loop) no more exists.

> 3. MEMDISK: There were several programs I can boot from my USB setup by
> including syslinux memdisk. These now fail due to memdisk error - for
> example (<...> means options I have tried): menuentry "HDT: hardware
> diagnostics tool" { set root="http,192.168.2.100" set
> memfile="/pub/tftp/rescue/rscd/memdisk" set
> isofile="/pub/tftp/rescue/rscd/hdt.img" linux16  ($root)$memfile
> <keeppxe floppy raw safeint> initrd16 ($root)$isofile	}
> With PXE, memdisk may need to be replaced with gpxelinux.0, but that
> will require using Grub's broken pxechain. Is there a better way to do
> this? syslinux apparently can also use memdisk for iso booting KERNEL
> memdisk  \  APPEND iso initrd=http://192.168.2.100/path/isofile.iso
> 

I briefly tested memdisk from syslinux 4.04 with hdt.img 0.5.2 under
grub master head and it works. I did in in qemu if it makes difference.
Files were local but I do not expect any difference (when memdisk gets
control, both files are loaded in memory already).

> 4. I think it would be a great idea if known grub.cfg entries could be
> listed in the official Grub-wiki. The distro maintainers might also be
> convinced or willing to post their code and solutions regarding iso
> loopback from HDD/USB/PXE variations. I don't know, Just an idea...
>