nixos: Initial netbooting installer

nixos/modules/build.nix

@@ -1,6 +1,6 @@
 { lib, pkgs, extendModules, modulesPath, options, config, ... }:
 let
-  inherit (lib) recursiveUpdate mkOption mkDefault mkIf mkMerge flatten optional;
+  inherit (lib) recursiveUpdate mkOption mkDefault mkIf mkMerge mkForce flatten optional;
   inherit (lib.my) mkBoolOpt' dummyOption;
 
   cfg = config.my.build;
@@ -43,15 +43,144 @@ let
     modules = flatten [
       "${modulesPath}/installer/netboot/netboot.nix"
       allHardware
+    ];
+  };
+
+  asNetboot = extendModules {
+    modules = flatten [
+      allHardware
       ({ pkgs, config, ... }: {
-        system.build.netbootArchive = pkgs.runCommand "netboot-${config.system.name}-archive.tar" { } ''
-          ${pkgs.gnutar}/bin/tar -rvC "${config.system.build.kernel}" \
-            -f "$out" "${config.system.boot.loader.kernelFile}"
-          ${pkgs.gnutar}/bin/tar -rvC "${config.system.build.netbootRamdisk}" \
-            -f "$out" initrd
-          ${pkgs.gnutar}/bin/tar -rvC "${config.system.build.netbootIpxeScript}" \
-            -f "$out" netboot.ipxe
-        '';
+        boot = {
+          loader.grub.enable = false;
+          initrd = {
+            kernelModules = [ "nbd" ];
+
+            systemd = {
+              storePaths = with pkgs; [
+                gnused
+                nbd
+                netcat
+              ];
+              extraBin = with pkgs; {
+                dmesg = "${util-linux}/bin/dmesg";
+                ip = "${iproute2}/bin/ip";
+                nbd-client = "${nbd}/bin/nbd-client";
+              };
+              extraConfig = ''
+                DefaultTimeoutStartSec=10
+                DefaultDeviceTimeoutSec=10
+              '';
+
+              network = {
+                enable = true;
+                wait-online.enable = true;
+
+                networks."10-netboot" = {
+                  matchConfig.Name = "et-boot";
+                  DHCP = "yes";
+                };
+              };
+
+              services = {
+                nbd = {
+                  description = "NBD Root FS";
+
+                  script = ''
+                    get_cmdline() {
+                      ${pkgs.gnused}/bin/sed -rn "s/^.*$1=(\\S+).*\$/\\1/p" < /proc/cmdline
+                    }
+
+                    s="$(get_cmdline nbd_server)"
+                    until ${pkgs.netcat}/bin/nc -zv "$s" 22; do
+                      sleep 0.1
+                    done
+
+                    exec ${pkgs.nbd}/bin/nbd-client -systemd-mark -N "$(get_cmdline nbd_export)" "$s" /dev/nbd0
+                  '';
+                  unitConfig = {
+                    IgnoreOnIsolate = "yes";
+                    DefaultDependencies = "no";
+                  };
+                  serviceConfig = {
+                    Type = "forking";
+                    Restart = "on-failure";
+                    RestartSec = 10;
+                  };
+
+                  wantedBy = [ "initrd-root-device.target" ];
+                };
+              };
+            };
+          };
+
+          postBootCommands = ''
+            # After booting, register the contents of the Nix store
+            # in the Nix database in the COW root.
+            ${config.nix.package}/bin/nix-store --load-db < /nix-path-registration
+
+            # nixos-rebuild also requires a "system" profile and an
+            # /etc/NIXOS tag.
+            touch /etc/NIXOS
+            ${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system
+          '';
+        };
+
+        programs.nbd.enable = true;
+
+        fileSystems = {
+          "/" = {
+            fsType = "ext4";
+            device = "/dev/nbd0";
+            noCheck = true;
+            autoResize = true;
+          };
+        };
+
+        networking.useNetworkd = mkForce true;
+
+        systemd = {
+          network.networks."10-boot" = {
+            matchConfig.Name = "et-boot";
+            DHCP = "yes";
+            networkConfig.KeepConfiguration = "yes";
+          };
+        };
+
+        system.build = {
+          rootImage = pkgs.callPackage "${modulesPath}/../lib/make-ext4-fs.nix" {
+            storePaths = [ config.system.build.toplevel ];
+            volumeLabel = "netboot-root";
+          };
+          netbootScript = pkgs.writeText "boot.ipxe" ''
+            #!ipxe
+            kernel ${pkgs.stdenv.hostPlatform.linux-kernel.target} init=${config.system.build.toplevel}/init initrd=initrd ifname=et-boot:''${mac} nbd_server=''${next-server} ${toString config.boot.kernelParams} ''${cmdline}
+            initrd initrd
+            boot
+          '';
+
+          netbootTree = pkgs.linkFarm "netboot-${config.system.name}" [
+            {
+              name = config.system.boot.loader.kernelFile;
+              path = "${config.system.build.kernel}/${config.system.boot.loader.kernelFile}";
+            }
+            {
+              name = "initrd";
+              path = "${config.system.build.initialRamdisk}/initrd";
+            }
+            {
+              name = "rootfs.ext4";
+              path = config.system.build.rootImage;
+            }
+            {
+              name = "boot.ipxe";
+              path = config.system.build.netbootScript;
+            }
+          ];
+          netbootArchive = pkgs.runCommand "netboot-${config.system.name}.tar.zst" { } ''
+            export PATH=${pkgs.zstd}/bin:$PATH
+            ${pkgs.gnutar}/bin/tar --dereference --zstd -cvC ${config.system.build.netbootTree} -f "$out" .
+          '';
+        };
       })
     ];
   };
@@ -77,6 +206,7 @@ in
       asISO = mkAsOpt asISO "a bootable .iso image";
       asContainer = mkAsOpt asContainer "a container";
       asKexecTree = mkAsOpt asKexecTree "a kexec-able kernel and initrd";
+      asNetboot = mkAsOpt asNetboot "a netboot-able kernel initrd, and iPXE script";
 
       buildAs = options.system.build;
     };
@@ -110,7 +240,8 @@ in
         iso = config.my.asISO.config.system.build.isoImage;
         container = config.my.asContainer.config.system.build.toplevel;
         kexecTree = config.my.asKexecTree.config.system.build.kexecTree;
-        netbootArchive = config.my.asKexecTree.config.system.build.netbootArchive;
+        netbootTree = config.my.asNetboot.config.system.build.netbootTree;
+        netbootArchive = config.my.asNetboot.config.system.build.netbootArchive;
       };
     };
   };