[bug#45225] [PATCH] gnu: grub: Fix unicode font loading when booting over TFTP.

[Stefan]

Hi Ludo’!

> I’m not sure I understand what this change meant to fix though.  What
> was the initial problem that led to the addition of this
> ‘canonicalize-path’ call?

When I am booting over TFTP, the Guix related files are located somewhere on 
that server and therefore symlinks do not work. Let's make an example:

There is some path like /volume/systems/guix-system/. There you can find 
gnu/store/ and boot/.

That server serves /volume/systems/guix-system/ via NFS as the root file system 
for a raspberry. That server also serves /volume/systems/guix-system/boot/ as 
the TFTP root for booting.

Now due to the fact that I need some firmware, configuration files, U-Boot and 
GRUB, there is now the possibility to create a bootloader-profile, which is 
basically a collection of symlinks to all this.

Due to this, there is somewhere a 
/volume/systems/guix-system/gnu/store/…-bootloader-profile/share/grub/unicode.pf2,
 which is an *absolute* symlink to 
/gnu/store/…-grub-efi-2.04/share/grub/unicode.pf2. 

The generated grub.cfg now normally refers to 
/gnu/store/…-bootloader-profile/share/grub/unicode.pf2.

When GRUB tries to load gnu/store/…-bootloader-profile/share/grub/unicode.pf2 
via TFTP, due to a profile prepared *relative* symlink at 
/volume/systems/guix-system/boot/gnu/store to the real store location at 
../..gnu/store/guix-system/gnu/store/ the TFTP server is able to access 
gnu/store/…-bootloader-profile/share/grub/unicode.pf2.

And there is the problem: That 
/gnu/store/…-bootloader-profile/share/grub/unicode.pf2 is an *absolute* symlink 
with no meaning to the TFTP server, so loading the font fails.

Simply speaking: Files for booting via TFTP must not be *absolute* symlinks.

Meanwhile I know that the font can be referred to as simply "unicode" without 
any path and extension, as it is installed with install-grub-efi, 
install-grub-efi-netboot and install-grub. I’m just still unsure about 
install-grub-disk-image. So hopefully the font reference can be simplified.

> Yeah, I wanted to send you a heads-up and then I forgot, apologies!

Nevermind. I’m sorry to have caused this trouble.

> In general, my suggestion when fiddling with these things is to at least
> run …

My trouble is that I only have that raspberry with only 1 GB RAM yet, and 
running tests on it is kind of impossible.

I tried to install Guix in a virtual machine on a NAS system during the 
weekend. The installation image is working, but the installed system hangs 
during boot. At least this was enough to find out that a simple "unicode" in 
grub.cfg is also sufficient for install-grub. :-)

I’m sorry that I broke Guix. I didn’t imagine that a canonicalize-path would 
not work, when the store path is known during build.

But this brings me back to my original question: Could you please explain why 
the grub package, which is referred to with a file-append gexp, is finally not 
visible when the grub.cfg is created?


Bye

Stefan