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Merge pull request #92122 from nh2/qemu-vm-fix-useBootLoader

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qemu-vm: Fix useBootLoader, remove `/boot` read-only restriction
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Niklas Hambüchen 2020-07-06 22:06:20 +02:00 committed by GitHub
commit d4d9d9c552
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2 changed files with 41 additions and 4 deletions
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2
nixos/doc/manual/man-nixos-rebuild.xml
View File

@ -315,7 +315,7 @@
switch</command>), because the hardware and boot loader configuration in
the VM are different. The boot loader is installed on an automatically
generated virtual disk containing a <filename>/boot</filename>
partition, which is mounted read-only in the VM.
partition.
</para>
</listitem>
</varlistentry>

43
nixos/modules/virtualisation/qemu-vm.nix
View File

@ -176,6 +176,8 @@ let
# Generate a hard disk image containing a /boot partition and GRUB
# in the MBR. Used when the `useBootLoader' option is set.
# Uses `runInLinuxVM` to create the image in a throwaway VM.
# See note [Disk layout with `useBootLoader`].
# FIXME: use nixos/lib/make-disk-image.nix.
bootDisk =
pkgs.vmTools.runInLinuxVM (
@ -210,6 +212,19 @@ let
--partition-guid=2:970C694F-AFD0-4B99-B750-CDB7A329AB6F \
--hybrid 2 \
--recompute-chs /dev/vda
${optionalString (config.boot.loader.grub.device != "/dev/vda")
# In this throwaway VM, we only have the /dev/vda disk, but the
# actual VM described by `config` (used by `switch-to-configuration`
# below) may set `boot.loader.grub.device` to a different device
# that's nonexistent in the throwaway VM.
# Create a symlink for that device, so that the `grub-install`
# by `switch-to-configuration` will hit /dev/vda anyway.
''
ln -s /dev/vda ${config.boot.loader.grub.device}
''
}
${pkgs.dosfstools}/bin/mkfs.fat -F16 /dev/vda2
export MTOOLS_SKIP_CHECK=1
${pkgs.mtools}/bin/mlabel -i /dev/vda2 ::boot
@ -510,7 +525,27 @@ in
config = {
boot.loader.grub.device = mkVMOverride cfg.bootDevice;
# Note [Disk layout with `useBootLoader`]
#
# If `useBootLoader = true`, we configure 2 drives:
# `/dev/?da` for the root disk, and `/dev/?db` for the boot disk
# which has the `/boot` partition and the boot loader.
# Concretely:
#
# * The second drive's image `disk.img` is created in `bootDisk = ...`
# using a throwaway VM. Note that there the disk is always `/dev/vda`,
# even though in the final VM it will be at `/dev/*b`.
# * The disks are attached in `virtualisation.qemu.drives`.
# Their order makes them appear as devices `a`, `b`, etc.
# * `fileSystems."/boot"` is adjusted to be on device `b`.
# If `useBootLoader`, GRUB goes to the second disk, see
# note [Disk layout with `useBootLoader`].
boot.loader.grub.device = mkVMOverride (
if cfg.useBootLoader
then driveDeviceName 2 # second disk
else cfg.bootDevice
);
boot.initrd.extraUtilsCommands =
''
@ -602,6 +637,8 @@ in
driveExtraOpts.werror = "report";
}]
(mkIf cfg.useBootLoader [
# The order of this list determines the device names, see
# note [Disk layout with `useBootLoader`].
{
name = "boot";
file = "$TMPDIR/disk.img";
@ -656,9 +693,9 @@ in
};
} // optionalAttrs cfg.useBootLoader
{ "/boot" =
{ device = "${lookupDriveDeviceName "boot" cfg.qemu.drives}2";
# see note [Disk layout with `useBootLoader`]
{ device = "${lookupDriveDeviceName "boot" cfg.qemu.drives}2"; # 2 for e.g. `vdb2`, as created in `bootDisk`
fsType = "vfat";
options = [ "ro" ];
noCheck = true; # fsck fails on a r/o filesystem
};
});