Comment 9 for bug 1827929

> On Fri, May 22, 2020 at 04:09:51PM -0000, Ryan Harper wrote:
> > We will need two formats for the hybrid mode, ptable: gpt and ptable:
> > dos
>
> I don't see why this should be the case. Are we not emitting GPT everywhere
> today, even when the system is booting in BIOS mode? Late-model BIOSes do
> support booting from GPT; I would think at this point anything that doesn't
> support GPT is too old to be of practical concern.
>
> So a GPT table with a bios_grub partition and an EFI System Partition should
> suffice.

Curtin has to deal with either construct; The design of the storage config is
from MAAS, Subiquity, user-defined autoconf install, Field Engineer creating a
one-off, etc. What I'm saying here is that curtin should validate that
one can create a hybrid partition layout with either GPT and MSDOS. Note,
I first saw such a dos-based hybrid looking at the partition layout of our
own installer iso. =)

"/dev/sdc": {
    "ID_FS_LABEL": "Ubuntu-Server_18.04.3_LTS_amd64",
    "ID_FS_UUID_ENC": "2019-08-05-20-00-00-00",
    "ID_FS_LABEL_ENC": "Ubuntu-Server\\x2018.04.3\\x20LTS\\x20amd64",
    "ID_BUS": "usb",
    "ID_FS_BOOT_SYSTEM_ID": "EL\\x20TORITO\\x20SPECIFICATION",
    "ID_FS_TYPE": "iso9660",
    "DEVNAME": "/dev/sdc",
    "ID_PART_TABLE_TYPE": "dos",
    "partitiontable": {
        "label": "dos",
        "id": "0x2f10bd40",
        "unit": "sectors",
        "partitions": [
            {
                "bootable": true,
                "size": 1736704,
                "type": "0",
                "node": "/dev/sdc1",
                "start": 0
            },
            {
                "size": 4928,
                "type": "ef",
                "node": "/dev/sdc2",
                "start": 1295064
            }
        ],
        "device": "/dev/sdc"
    },
},

>
> > For gpt, the config from comment #1 applies, we'll have both bios_grub
> > and an efi partition (possibly a secondary for resilient boot).
>
> Resilient boot is only applicable in the case of multiple disks; and then

Yes

> each disk in the root set should have exactly one ESP and exactly one
> bios_grub partition.

Yes. We currently are testing UEFI with GPT layout only; with hybrid we
need to test that resilient boot works with the MSDOS hybrid layout as well.