69 lines
2.4 KiB
Nix
69 lines
2.4 KiB
Nix
# This module creates a virtual machine from the NixOS configuration.
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# Building the `config.system.build.vm' attribute gives you a command
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# that starts a KVM/QEMU VM running the NixOS configuration defined in
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# `config'. The Nix store is shared read-only with the host, which
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# makes (re)building VMs very efficient. However, it also means you
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# can't reconfigure the guest inside the guest - you need to rebuild
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# the VM in the host. On the other hand, the root filesystem is a
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# read/writable disk image persistent across VM reboots.
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{config, pkgs, ...}:
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{
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# All the modules the initrd needs to mount the host filesystem via
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# CIFS. Also use paravirtualised network and block devices for
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# performance.
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boot.initrd.extraKernelModules =
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["cifs" "virtio_net" "virtio_pci" "virtio_blk" "virtio_balloon" "nls_utf8"];
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boot.initrd.postDeviceCommands =
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''
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ipconfig 10.0.2.15:::::eth0:none
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'';
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# Mount the host filesystem via CIFS, and bind-mount the Nix store
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# of the host into our own filesystem.
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fileSystems =
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[ { mountPoint = "/";
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device = "/dev/vda";
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}
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{ mountPoint = "/hostfs";
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device = "//10.0.2.4/qemu";
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fsType = "cifs";
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options = "guest,username=nobody";
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neededForBoot = true;
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}
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{ mountPoint = "/nix/store";
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device = "/hostfs/nix/store";
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options = "bind";
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neededForBoot = true;
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}
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];
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# Starting DHCP brings down eth0, which kills the connection to the
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# host filesystem and thus deadlocks the system.
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networking.useDHCP = false;
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system.build.vm = pkgs.runCommand "nixos-vm" {}
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''
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ensureDir $out
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ln -s ${config.system.build.system} $out/system
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ensureDir $out/bin
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cat > $out/bin/run-nixos-vm <<EOF
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#! ${pkgs.stdenv.shell}
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export PATH=${pkgs.samba}/sbin:\$PATH
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${pkgs.kvm}/bin/qemu-system-x86_64 \
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-net nic,model=virtio -net user -smb / \
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-drive file=\$diskImage,if=virtio,boot=on \
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-kernel ${config.system.build.system}/kernel \
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-initrd ${config.system.build.system}/initrd \
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-append "\$(cat ${config.system.build.system}/kernel-params) init=${config.system.build.bootStage2} systemConfig=${config.system.build.system}"
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EOF
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chmod u+x $out/bin/run-nixos-vm
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'';
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# sendfile() is currently broken over CIFS, so fix it here for all
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# configurations that use Apache.
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services.httpd.extraConfig = "EnableSendFile Off";
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}
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