grub-netboot.cfg does not load $prefix/$platform/grub.cfg

[Michael Hudson-Doyle]

grub-netboot.cfg (the config that is embedded in grubnetx64.efi / grubnetaa64.efi looks like this:

cat >"$workdir/grub-netboot.cfg" <<EOF
if [ -e \$prefix/$platform/grub.cfg ]; then
 source \$prefix/$platform/grub.cfg
else
 source \$prefix/grub.cfg
fi
EOF

This looks like the intent is to load e.g. grub/x86_64-efi/grub.cfg off your tftp or http server if it exists and if not fall back to grub/grub.cfg. But this doesn't work: -e never returns true for a network path afaict and so grub always tries to load grub/grub.cfg instead.

I first thought that this was expected / by design but on reading the patches we carry to grub I'm not completely sure and maybe this is a bug in grub rather than a pointer that writing the config like this is pointless. But the config definitely doesn't work as expected.