boot.initrd.network: Support DHCP

This allows us to use it for EC2 instances.

2 files changed, 58 insertions, 45 deletions

diff --git a/nixos/modules/system/boot/initrd-network.nix b/nixos/modules/system/boot/initrd-network.nix
index e1e49bce6938..abf88734a558 100644
--- a/nixos/modules/system/boot/initrd-network.nix
+++ b/nixos/modules/system/boot/initrd-network.nix
@@ -6,6 +6,23 @@ let
 
   cfg = config.boot.initrd.network;
 
+  udhcpcScript = pkgs.writeScript "udhcp-script"
+    ''
+      #! /bin/sh
+      if [ "$1" = bound ]; then
+        ip address add "$ip/$mask" dev "$interface"
+        if [ -n "$router" ]; then
+          ip route add default via "$router" dev "$interface"
+        fi
+        if [ -n "$dns" ]; then
+          rm -f /etc/resolv.conf
+          for i in $dns; do
+            echo "nameserver $dns" >> /etc/resolv.conf
+          done
+        fi
+      fi
+    '';
+
 in
 
 {
@@ -16,10 +33,13 @@ in
       type = types.bool;
       default = false;
       description = ''
-        Add network connectivity support to initrd.
-
-        Network options are configured via <literal>ip</literal> kernel
-        option, according to the kernel documentation.
+        Add network connectivity support to initrd. The network may be
+        configured using the <literal>ip</literal> kernel parameter,
+        as described in <link
+        xlink:href="https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt">the
+        kernel documentation</link>.  Otherwise, if
+        <option>networking.useDHCP</option> is enabled, an IP address
+        is acquired using DHCP.
       '';
     };
 
@@ -43,18 +63,35 @@ in
       copy_bin_and_libs ${pkgs.mkinitcpio-nfs-utils}/bin/ipconfig
     '';
 
-    boot.initrd.preLVMCommands = ''
-      # Search for interface definitions in command line
-      for o in $(cat /proc/cmdline); do
-        case $o in
-          ip=*)
-            ipconfig $o && hasNetwork=1
-            ;;
-        esac
-      done
-
-      ${cfg.postCommands}
-    '';
+    boot.initrd.preLVMCommands =
+      # Search for interface definitions in command line.
+      ''
+        for o in $(cat /proc/cmdline); do
+          case $o in
+            ip=*)
+              ipconfig $o && hasNetwork=1
+              ;;
+          esac
+        done
+      ''
+
+      # Otherwise, use DHCP.
+      + optionalString config.networking.useDHCP ''
+        if [ -z "$hasNetwork" ]; then
+
+          # Bring up all interfaces.
+          for iface in $(cd /sys/class/net && ls); do
+            echo "bringing up network interface $iface..."
+            ip link set "$iface" up
+          done
+
+          # Acquire a DHCP lease.
+          echo "acquiring IP address via DHCP..."
+          udhcpc --quit --now --script ${udhcpcScript}
+        fi
+      ''
+
+      + cfg.postCommands;
 
   };
 
diff --git a/nixos/modules/virtualisation/amazon-image.nix b/nixos/modules/virtualisation/amazon-image.nix
index dd2cdd43f31c..7d16206517d4 100644
--- a/nixos/modules/virtualisation/amazon-image.nix
+++ b/nixos/modules/virtualisation/amazon-image.nix
@@ -8,28 +8,7 @@
 
 with lib;
 
-let
-
-  cfg = config.ec2;
-
-  udhcpcScript = pkgs.writeScript "udhcp-script"
-    ''
-      #! /bin/sh
-      if [ "$1" = bound ]; then
-        ip address add "$ip/$mask" dev "$interface"
-        if [ -n "$router" ]; then
-          ip route add default via "$router" dev "$interface"
-        fi
-        if [ -n "$dns" ]; then
-          rm -f /etc/resolv.conf
-          for i in $dns; do
-            echo "nameserver $dns" >> /etc/resolv.conf
-          done
-        fi
-      fi
-    '';
-
-in
+let cfg = config.ec2; in
 
 {
   imports = [ ../profiles/headless.nix ./ec2-data.nix ./amazon-grow-partition.nix ./amazon-init.nix ];
@@ -41,10 +20,7 @@ in
       autoResize = true;
     };
 
-    boot.initrd.kernelModules =
-      [ "xen-blkfront" "xen-netfront"
-        "af_packet" # <- required by udhcpc
-      ];
+    boot.initrd.kernelModules = [ "xen-blkfront" "xen-netfront" ];
     boot.kernelParams = mkIf cfg.hvm [ "console=ttyS0" ];
 
     # Prevent the nouveau kernel module from being loaded, as it
@@ -67,6 +43,8 @@ in
         kill -9 -1
       '';
 
+    boot.initrd.network.enable = true;
+
     # Mount all formatted ephemeral disks and activate all swap devices.
     # We cannot do this with the ‘fileSystems’ and ‘swapDevices’ options
     # because the set of devices is dependent on the instance type
@@ -79,12 +57,10 @@ in
     boot.initrd.postMountCommands =
       ''
         metaDir=$targetRoot/etc/ec2-metadata
-        mkdir -m 0755 $targetRoot/etc
+        mkdir -m 0755 -p $targetRoot/etc
         mkdir -m 0700 -p "$metaDir"
 
         echo "getting EC2 instance metadata..."
-        ip link set eth0 up
-        udhcpc --interface eth0 --quit --now --script ${udhcpcScript}
 
         if ! [ -e "$metaDir/ami-manifest-path" ]; then
           wget -q -O "$metaDir/ami-manifest-path" http://169.254.169.254/1.0/meta-data/ami-manifest-path