Add filesystem option to automatically grow to the maximum size

This is primarily for EC2 and other cloud environments, where the disk
may be bigger than the original image.

nixos/modules/system/boot/stage-1-init.sh

@@ -290,10 +290,23 @@ mountFS() {
         if [ -z "$fsType" ]; then fsType=auto; fi
     fi
 
-    echo "$device /mnt-root$mountPoint $fsType $options" >> /etc/fstab
+    # Filter out x- options, which busybox doesn't do yet.
+    local optionsFiltered="$(IFS=,; for i in $options; do if [ "${i:0:2}" != "x-" ]; then echo -n $i,; fi; done)"
+
+    echo "$device /mnt-root$mountPoint $fsType $optionsFiltered" >> /etc/fstab
 
     checkFS "$device" "$fsType"
 
+    # Optionally resize the filesystem.
+    case $options in
+        *x-nixos.autoresize*)
+            if [ "$fsType" = ext2 -o "$fsType" = ext3 -o "$fsType" = ext4 ]; then
+                echo "resizing $device..."
+                resize2fs "$device"
+            fi
+            ;;
+    esac
+
     # Create backing directories for unionfs-fuse.
     if [ "$fsType" = unionfs-fuse ]; then
         for i in $(IFS=:; echo ${options##*,dirs=}); do

nixos/modules/system/boot/stage-1.nix

@@ -70,6 +70,12 @@ let
       copy_bin_and_libs ${pkgs.kmod}/bin/kmod
       ln -sf kmod $out/bin/modprobe
 
+      # Copy resize2fs if needed.
+      ${optionalString (any (fs: fs.autoResize) (attrValues config.fileSystems)) ''
+        # We need mke2fs in the initrd.
+        copy_bin_and_libs ${pkgs.e2fsprogs}/sbin/resize2fs
+      ''}
+
       ${config.boot.initrd.extraUtilsCommands}
 
       # Copy ld manually since it isn't detected correctly
@@ -393,7 +399,6 @@ in
       }
     ];
 
-
     system.build.bootStage1 = bootStage1;
     system.build.initialRamdisk = initialRamdisk;
     system.build.extraUtils = extraUtils;