Re: Chainloading an MS Windows installer DVD

[SteveSi]

If you copy the *contents *of a Windows Install ISO to a FAT32 partition,
then you should be able to boot to WinPE, run Setup and install Windows.

e.g. I booted to a USB drive which had grub2 on partition 2 and the
extracted windows ISO files on partition 3 FAT32

I simply used chainloader (hd0,msdos3)/efi/boot/bootx64.efi




On Tue, 24 Oct 2023 at 05:08, Andrei Borzenkov <arvidjaar@gmail.com> wrote:

> On 24.10.2023 00:36, Philip Couling wrote:
> > Thanks both, this is really insightful!
> >
> > Can I just echo back in layman's terms to check I've understood.  You're
> > telling me that there is some protocol to tell the EFI binary which drive
> > it was loaded from and thus give it a was to go find its other resources
> on
> > disk.
>
> Correct. In this case the only resources available to the early
> bootloader are those that can be accessed via firmware and this means
> EFI boot image which is presented by EFI as separate device. And path to
> which is lost by grub2.
>
> > What you are saying is that this is either unsuccessful when the ISO
> > is flashed to a USB
>
> I already told you that you need to present accurate and complete facts.
> This is the first time you ever mentioned "flashing to USB". Your title
> says "installer DVD", your OP says "UDF" which both imply booting DVD
> image as CD/DVD. I tested it when booted as CD/DVD drive.
>
> > or otherwise impossible if the ISO is loaded as a grub
> > loop device.
> >
>
> Again - this is the very first time you even mention "grub loop device".
> If you described what you did from the very beginning, the answer would
> be immediate - it will not work.
>
> > That's actually really helpful to understand. Thanks
> >
> > On Mon, 23 Oct 2023 at 21:29, SteveSi <easy2boot@gmail.com> wrote:
> >
> >> Even if it did boot, Windows setup would not be able to find the
> >> install.wim file which is inside the iso, so you would get a 'Missing
> >> DVD/CD drive driver' message.
>
> Huh? You are claiming that Windows installer image cannot be used to
> install Windows?
>
> >> Most multiboot solutions which boot windows ISO files, use a pxe wimboot
> >> grub2 module. So the boot.wim file is loaded from the loopback iso grub2
> >> device and it then boots to winpe.
> >> Files are also injected into the boot ram image which then loads the iso
> >> file as a virtual dvd so that setup will see the install.wim file on a
> >> mounted volume.
> >>
> >>
> >> On Mon, 23 Oct 2023, 20:23 Andrei Borzenkov, <arvidjaar@gmail.com>
> wrote:
> >>
> >>> On 23.10.2023 11:58, Philip Couling wrote:
> >>>> Really I've been as precise as I can and given everything I've seen.
> It
> >>>> was actually the minimalist output that prompted me to come ask. Yes
> >>> that
> >>>> was all of the output.
> >>>>
> >>>> I'll investigate further if that points to an error on my part. I
> assume
> >>>> setting root=... is enough to set the device path. But to be clear:
> no,
> >>> the
> >>>> only output from the chainloader command was "/EndEntire".
> >>>>
> >>>
> >>> It implies that $root could not be opened or is empty. I cannot
> >>> reproduce it with openSUSE Tumbleweed grub2, but that is because as I
> >>> mentioned it is heavily patched and is always using the device from the
> >>> chainloader argument.
> >>>
> >>>> I didn't realise distributions had customised grub in that way. I'm
> >>> using
> >>>> the Ubuntu (22.04) release. If you think that may be a problem I can
> >>> retry
> >>>> with upstream version.
> >>>>
> >>>
> >>> I do not know what changed are in Ubuntu.
> >>>
> >>>> If you know of a way to get more debug info out of the chainloader or
> >>>> command boot command because I was really hoping for more than
> "Unknown
> >>>> Error" too!
> >>>>
> >>>
> >>> Not without recompiling grub.
> >>>
> >>> Anyway, my best guess is that Windows primary bootloader fails to find
> >>> (or read) its CD. grub2 plays some tricks with EFI CD device paths. So
> >>> device path that it associated with loaded image is not CD media device
> >>> path, but (parent) block device path. It is quite possible that Windows
> >>> loader is not prepared to handle it. As a simple example - EFI CD media
> >>> handle has simple file protocol that allows reading it; while block
> >>> device does not have it.
> >>>
> >>> I tried to boot cdboot.efi instead and I get "Press and key to boot
> from
> >>> CD ..." and then it fails as well which sort of confirms my guess (that
> >>> loaded image is started but fails).
> >>>
> >>> If my guess is correct, I right now do not see how to make it work.
> >>> grub2 simply does not expose media CD path (which points to the
> >>> underlying EFI "system partition" boot image on CD).
> >>>
> >>>> On Mon, 23 Oct 2023 at 08:25, Andrei Borzenkov <arvidjaar@gmail.com>
> >>> wrote:
> >>>>
> >>>>> On Thu, Oct 19, 2023 at 12:36 PM Philip Couling <couling@gmail.com>
> >>> wrote:
> >>>>>>
> >>>>>> Hi
> >>>>>>
> >>>>>> Is there any reason why I can't chainload an MS Windows Installer
> (on
> >>>>>> USB)?  Currently when I try this I get "UnknownError" when I type
> >>> "boot"
> >>>>> at
> >>>>>> the grub command line.
> >>>>>>
> >>>>>> The MS Windows ISOs are a bit weird: found here:
> >>>>>> https://www.microsoft.com/en-gb/software-download/windows10ISO
> >>>>>>
> >>>>>> They are not partitioned and have a UDF filesystem instead of ISO
> >>> 9660 or
> >>>>>> FAT32. So my hardware cannot directly boot this.  But I was assuming
> >>> that
> >>>>>> all I would need to do would be ask grub to chainload the ISO as it
> >>> has a
> >>>>>> UDF driver.
> >>>>>>
> >>>>>> I can read the Windows Boot media after I "insmod udf" and then
> >>>>>> "chainloader /efi/boot/bootx64.efi" which results in the output
> >>>>>> "/EndEntire".
> >>>>>
> >>>>> Is it really *all* that is printed? Because grub should print the
> >>>>> device path and it sounds like it is empty? Always provide complete
> >>>>> and accurate information, not some random part of it. At the very
> >>>>> least there should be "file path: " somewhere before "/EndEntire".
> >>>>>
> >>>>>> But when I then type "boot" I get "UnknownError".
> >>>>>>
> >>>>>
> >>>>> grub should really print the EFI error in this case to help in
> >>>>> troubleshooting such issues.
> >>>>>
> >>>>>> Has anyone experienced this? Any ideas about what isn't working? I
> >>> freely
> >>>>>
> >>>>> Assuming you are using the current upstream code (because in the past
> >>>>> EFI chainloader was heavily patched by distributions) grub reads the
> >>>>> content of EFI binary in memory, creates an instance of loaded image
> >>>>> from it and then calls EFI start image function. I would refrain from
> >>>>> guessing what could have gone wrong until you provide more precise
> >>>>> information.
> >>>>>
> >>>>>> admit it could be a Microsoft weirdness that requires their input, I
> >>> just
> >>>>>> wanted to exhaust options here first.
> >>>>>>
> >>>>>> Thanks
> >>>>>
> >>>>
> >>>
> >>>
> >>>
> >
>
>
>

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