The transition to markdown is done now and the historical trivia is not
helpful for first time contributers who are the primary audience for
this document. Telling the user to edit a file by editing a file is
superfluous.
By some miracle, before, it was possible to reconnect to the `node1` without
doing any relevant dance.
But now we are direct booting (¿), it seems like we need to do the right things.
This introduces a `check_output` flag for `execute` because we do not want to steal the
messages from the backdoor service as we might execute the kexec too fast compared
to when we will reconnect.
Therefore, we will let the message in the pipe if needed.
There's no reason to use a bootloader when testing kexec, this is a feature
that reboots *directly* in the kernel, if anything, we should just direct boot the
kernel and reboots in the kernel.
A bootloader test really makes sense to test "default" systemctl kexec behavior which is already broken
because systemctl kexec will read the ESP to determine what to kexec by default.
This change removes the bespoke logic around identifying block devices.
Instead of trying to find the right device by iterating over
`qemu.drives` and guessing the right partition number (e.g.
/dev/vda{1,2}), devices are now identified by persistent names provided
by udev in /dev/disk/by-*.
Before this change, the root device was formatted on demand in the
initrd. However, this makes it impossible to use filesystem identifiers
to identify devices. Now, the formatting step is performed before the VM
is started. Because some tests, however, rely on this behaviour, a
utility function to replace this behaviour in added in
/nixos/tests/common/auto-format-root-device.nix.
Devices that contain neither a partition table nor a filesystem are
identified by their hardware serial number which is injecetd via QEMU
(and is thus persistent and predictable). PCI paths are not a reliably
way to identify devices because their availability and numbering depends
on the QEMU machine type.
This change makes the module more robust against changes in QEMU and the
kernel (non-persistent device naming) and by decoupling abstractions
(i.e. rootDevice, bootPartition, and bootLoaderDevice) enables further
improvement down the line.
