Do not add 1:1 dm-linear when root.img (/dev/xvda) is read-write. This
was to always have root device at /dev/mapper/dmroot, but unfortunately
grub can't parse it properly (fails at looking for partition number of
/dev/xvda1). There was a hack specifically for this, but it caused other
partitions on xvda unavailable.
On the other hand, symlink is enough to be able to mount always the same
device. Now, grub detect that root fs is on /dev/xvda1, which is
enough to have grub2-install working. Unfortunate effect is that it puts
root=/dev/xvda1 at kernel command line, which breaks AppVMs based on
this TemplateVM. But it's easier to fix kernel command line, than grub
device detection logic.
Fixes "initramfs: add support for root.img with partition table"
QubesOS/qubes-issues#2557
Installing grub on root.img require some space before the filesystem.
Create it by adding partition table to root.img. This commit take care
of assembling dmroot device when such partition table is present, while
preserving compatibility with partition-less images.
QubesOS/qubes-issues#2577
This hook require new device nodes to appear in /dev. If devtmpfs is
used, it's not a problem ("simple" initramfs case), but otherwise udevd
is needed - and it isn't running in pre-udev hook yet.
QubesOS/qubes-issues#2577
New version of sfdisk have different syntax for other units (suffixes
beside the numbers, instead of global --unit). The only common unit is
sector, so use that.
FixesQubesOS/qubes-issues#1427
This makes is possible to modify /lib/modules content - especially
install other kernel packages, without unmounting the whole
/lib/modules. Since dom0-provided modules will no longer conflict with
VM kernel packages (assuming kernel versions are different), there is no
need for qubes-kernel-vm-placeholder anymore.
Having only one subdirectory of /lib/modules mounted is somehow tricky,
because:
1. Directory name isn't always the same - it depends on kernel version.
This means that mountpoint must be created dynamically (so $NEWROOT must
be mounted in R/W for a moment).
2. There is one-command way to mount only a subdirectory of some
filesystem. So use a trick: mount it in some temporary directory, get
interesting subdir with `mount --bind`, then unmount temporary
directory.
QubesOS/qubes-issues#1354
