Add overlay for roll_dataset

Signed-off-by: magic_rb <richard@brezak.sk>

flake.nix

@@ -103,6 +103,7 @@
         overlays/itp
         overlays/virtiofsd-zfs
         overlays/show-files-to-be-deleted
+        overlays/rolling_datasets
 
         inputs.uterranix.flakeModule
       ];

overlays/rolling_datasets/bin/roll_dataset

@@ -0,0 +1,28 @@
+# -*- mode: shell-script -*-
+
+source @out@/share/functions/get_old_datasets
+
+if [[ "$#" != 3 ]] ; then
+    echo "This script requires precisely 2 arguments!"
+    exit 1
+fi
+
+dataset="$1"
+
+generation="$(zfs get :generation "$dataset" -H -o value)"
+generation="$(("$generation" + 1))"
+
+zfs set ":generation=$generation" "$dataset"
+zfs send "$dataset" | zfs recv "$dataset/$generation"
+zfs rollback "$dataset@blank" && echo "rollback complete"
+
+while IFS="\n" read gen
+do
+    printf "$gen < $(("$generation" - 10)) => "
+    if [ "$gen" -lt "$(("$generation" - 10))" ]; then
+        zfs destroy -r "$dataset/$gen"
+        echo "destroyed"
+    else
+        echo "kept"
+    fi
+done <<< "$(get_old_datasets "$dataset")"

overlays/rolling_datasets/default.nix

@@ -0,0 +1,67 @@
+{ inputs, ... }:
+{
+  flake.overlays.rolling_datasets =
+    final: prev:
+    let
+      writeTextFile =
+        { name # the name of the derivation
+        , text
+        , executable ? false # run chmod +x ?
+        , destination ? ""   # relative path appended to $out eg "/bin/foo"
+        , checkPhase ? ""    # syntax checks, e.g. for scripts
+        , env ? {}
+        }:
+        final.runCommand name
+          ({ inherit text executable;
+            passAsFile = [ "text" ];
+            # Pointless to do this on a remote machine.
+            preferLocalBuild = true;
+            allowSubstitutes = false;
+          } // env)
+          ''
+            n=$out${destination}
+            mkdir -p "$(dirname "$n")"
+
+            if [ -e "$textPath" ]; then
+              mv "$textPath" "$n"
+            else
+              echo -n "$text" > "$n"
+            fi
+
+            ${checkPhase}
+
+            (test -n "$executable" && chmod +x "$n") || true
+          '';
+      writeShellScriptBin = name : text : env :
+        writeTextFile {
+          inherit name;
+          executable = true;
+          destination = "/bin/${name}";
+          text = ''
+            #!${final.runtimeShell}
+            ${text}
+            '';
+          checkPhase = ''
+            ${final.stdenv.shell} -n $out/bin/${name}
+          '';
+        };
+    in
+      {
+        rolling_datasets =
+          final.runCommand "rolling_datasets" {
+
+          } ''
+            mkdir -p $out/bin
+            mkdir -p $out/share/functions
+
+            for binary in ${./bin}/* ; do
+              substituteAll "$binary" "$out/bin/$(basename "$binary")"
+            done
+
+            for function in ${./functions}/* ; do
+              substituteAll "$function" "$out/share/functions/$(basename "$function")"
+            done
+          '';
+      };
+}
+

overlays/rolling_datasets/functions/get_old_datasets

@@ -0,0 +1,6 @@
+# -*- mode: shell-script -*-
+function get_old_datasets()
+{
+  dataset="$1"
+  zfs list "$dataset" -t filesystem -r -H -o name | xargs -I {} ${final.runtimeShell} -c 'echo "$1" | rev | cut -f 1 -d "/" | rev' sh {} | grep -v "$dataset"
+}