Merge lp:~mwhudson/debian-cd/document-xorriso-options into lp:~ubuntu-cdimage/debian-cd/ubun3

[Michael Hudson-Doyle]

Add a lot of words. Do not change behaviour (hopefully).

[Steve Langasek (vorlon)]

I agree with the overall intent here, thanks.

review: Needs Information

[lp:~mwhudson/debian-cd/document-xorriso-options]

2080. By Michael Hudson-Doyle on 2020-07-08

expand "make various things unhappy"

[Michael Hudson-Doyle (mwhudson)]

ping

[Paride Legovini (paride)]

One inline comment, for the rest LGTM. I wonder if we'll ever be able to discontinue some of those legacy modes one day :)

review: Needs Fixing

[Paride Legovini (paride)]

The only difference I can see with the original command is that the

-eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot

options block and the

-append_partition 2 0xef cd-boot-images/usr/share/cd-boot-images-amd64/tree/boot/grub/efi.img

options block are swapped. I imagine you did it on purpose to add the boot options in a logical order:

- Legacy cdrom
- Legacy disk
- UEFI cdrom
- UEFI disk

I don't see a reason why the new options order shouldn't work, but I didn't test it.

Added another inline comment.

review: Needs Fixing

[lp:~mwhudson/debian-cd/document-xorriso-options]

2081. By Michael Hudson-Doyle on 2020-09-07

address review comments

[Michael Hudson-Doyle (mwhudson)]

Thanks for looking at this!!

> The only difference I can see with the original command is that the
>
> -eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot
>
> options block and the
>
> -append_partition 2 0xef cd-boot-images/usr/share/cd-boot-images-
> amd64/tree/boot/grub/efi.img
>
> options block are swapped. I imagine you did it on purpose to add the boot
> options in a logical order:
>
> - Legacy cdrom
> - Legacy disk
> - UEFI cdrom
> - UEFI disk

Right.

> I don't see a reason why the new options order shouldn't work, but I didn't
> test it.

I think I tested this at the time...

> Added another inline comment.

Thanks, fixed this and the other one.

[Paride Legovini (paride)]

LGTM, thanks!

review: Approve

[Steve Langasek (vorlon)]

review: Approve

=== modified file 'tools/boot/groovy/boot-amd64'
--- tools/boot/groovy/boot-amd64	2020-07-08 01:39:32 +0000
+++ tools/boot/groovy/boot-amd64	2020-09-07 11:33:14 +0000
@@ -45,7 +45,80 @@
 #
 # TODO test if --efi-boot-image can be used instead of -e
 
-echo -n "-J -joliet-long -l -b boot/grub/i386-pc/eltorito.img -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info --grub2-mbr cd-boot-images/usr/share/cd-boot-images-amd64/tree/boot/grub/i386-pc/boot_hybrid.img -append_partition 2 0xef cd-boot-images/usr/share/cd-boot-images-amd64/tree/boot/grub/efi.img -eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot -partition_offset 16 cd-boot-images/usr/share/cd-boot-images-amd64/tree" >> $N.mkisofs_opts
+mkisofs_opts ()
+{
+    printf "%s " $@ >> $N.mkisofs_opts
+}
+
+## Boring mkisofs options that should be set somewhere architecture independent.
+mkisofs_opts -J -joliet-long -l
+
+## Generalities on booting
+
+# There is a 2x2 matrix of boot modes we care about: legacy or UEFI
+# boot modes and having the installer be on a cdrom or a disk. Booting
+# from cdrom uses the el torito standard and booting from disk expects
+# a MBR or GPT partition table.
+#
+# https://wiki.osdev.org/El-Torito has a lot more background on this.
+
+## Set up the mkisofs options for legacy boot.
+
+# Set the el torito boot image "name", i.e. the path on the ISO
+# containing the bootloader for legacy-cdrom boot.
+mkisofs_opts -b boot/grub/i386-pc/eltorito.img
+
+# Back in the day, el torito booting worked by emulating a floppy
+# drive.  This hasn't been a useful way of operating for a long time.
+mkisofs_opts -no-emul-boot
+
+# Misc options to make the legacy-cdrom boot work.
+mkisofs_opts -boot-load-size 4 -boot-info-table --grub2-boot-info
+
+# The bootloader to write to the MBR for legacy-disk boot.
+#
+# Another approach is to use the very small isohdpfx.bin from isolinux
+# and -isohybrid-mbr to boot from a disk (isohdpfx.bin just jumps to
+# the legacy el torito boot block set up above) but this didn't work
+# when mwhudson tested it in July 2020.
+mkisofs_opts --grub2-mbr cd-boot-images/usr/share/cd-boot-images-amd64/tree/boot/grub/i386-pc/boot_hybrid.img
+
+## Set up the mkisofs options for UEFI boot.
+
+# Start a new entry in the el torito boot catalog.
+mkisofs_opts -eltorito-alt-boot
+
+# Specify where the el torito UEFI boot image "name", i.e. the path on
+# the ISO containing a FAT filesystem with a bootloader at the right
+# path (i.e. EFI/BOOT/BOOTX64.EFI).
+mkisofs_opts -e boot/grub/efi.img
+
+# Whether to emulate a floppy or not is a per-boot-catalog-entry
+# thing, so we need to say it again.
+mkisofs_opts -no-emul-boot
+
+# Add an ESP for uefi-disk boot.
+#
+# This is a very by hand way of doing it: it is possible to create a
+# partition table that points to the FAT filesystem above that will be
+# used by the uefi-cdrom boot. But it seems this leads to xorriso
+# creating a GPT that does not work; instead of creating a GPT with
+# overlapping partitions (which is not allowed by the spec) like so:
+#   | partition 1 / p1                                 |
+#             | ESP |
+# it splits the "main" partition so the partitions look like this:
+#   | p1      | ESP | p3                               |
+# which doesn't work at all when we mount p1 (it doesn't contain all
+# the files!)
+mkisofs_opts -append_partition 2 0xef cd-boot-images/usr/share/cd-boot-images-amd64/tree/boot/grub/efi.img
+
+## Create a partition table entry that covers the iso9660 filesystem.
+
+mkisofs_opts -partition_offset 16
+
+## Add the boot images from cd-boot-images-amd64 to the ISO.
+
+mkisofs_opts cd-boot-images/usr/share/cd-boot-images-amd64/tree
 
 default_kernel_params