full-disk support in vmtest

[vmagro]

• Antlir now supports building GPT images, vm infra should support booting these full disk images without specifying a kernel (+cmdline+initrd)
• Most of the 1 week timeline should be writing tests

[vmagro]

here is an example of building a gpt-formatted disk

antlir/antlir/compiler/test_images/BUCK

Line 1065 in e069008

image.gpt(

the image buck macro api unfortunately doesn't seem to have any documentation, but that example should be enough to get started
you will likely want to use image.rpms_install to install the kernel rpm from //third-party/fedora33:5.8.15-301.fc33.x86_64-core.rpm into the main rootfs layer, and then some combination of image.install / image.genrule_layer to get the initrd into the vfat partition for uefi (the initrd target should be //third-party/fedora33:5.8.15-301.fc33.x86_64-initrd, which a cpio archive that you can install into the vfat partition and the bootloader in qemu can load it and the vmlinuz)

this stackoverflow might be helpful to get qemu to work with a uefi bios to boot from a full partitioned disk image
https://unix.stackexchange.com/questions/52996/how-to-boot-efi-kernel-using-qemu-kvm