Add rollback functionality in nix-on-droid

modules/build/activation.nix

@@ -8,6 +8,8 @@ with lib;
 let
   cfg = config.build;
 
+  profileDirectory = "/nix/var/nix/profiles/nix-on-droid";
+
   # Programs that always should be available on the activation
   # script's PATH.
   activationBinPaths = lib.makeBinPath [
@@ -108,13 +110,6 @@ in
         internal = true;
         description = "Package containing /etc files.";
       };
-
-      profileDirectory = mkOption {
-        type = types.path;
-        readOnly = true;
-        internal = true;
-        description = "Path to nix-on-droid profile.";
-      };
     };
 
   };
@@ -126,8 +121,13 @@ in
 
     build = {
       activationAfter.linkProfile = ''
-        generationDir="$(dirname "$(realpath $0)")"
-        $DRY_RUN_CMD nix-env --profile "${cfg.profileDirectory}" --set "$generationDir"
+        generationDir="$(dirname $0)"
+
+        if [[ $generationDir =~ ^${profileDirectory}-([0-9]+)-link$ ]]; then
+          $DRY_RUN_CMD nix-env --profile "${profileDirectory}" --switch-generation "''${BASH_REMATCH[1]}"
+        else
+          $DRY_RUN_CMD nix-env --profile "${profileDirectory}" --set "$generationDir"
+        fi
       '';
 
       activationPackage =
@@ -151,8 +151,6 @@ in
             ln --symbolic ${config.environment.binSh} $out/filesystem/bin/sh
             ln --symbolic ${config.environment.usrBinEnv} $out/filesystem/usr/bin/env
           '';
-
-      profileDirectory = "/nix/var/nix/profiles/nix-on-droid";
     };
 
   };

nix-on-droid/nix-on-droid.sh

@@ -5,18 +5,24 @@ PATH=@coreutils@/bin:@nix@/bin:${PATH:+:}$PATH
 set -eu
 set -o pipefail
 
+PROFILE_DIRECTORY="/nix/var/nix/profiles/nix-on-droid"
+
 function errorEcho() {
     >&2 echo $@
 }
 
+function doGenerations() {
+    nix-env --profile $PROFILE_DIRECTORY --list-generations
+}
+
 function doHelp() {
     echo "Usage: $0 [OPTION] COMMAND"
     echo
     echo "Options"
     echo
-    echo "  -v|--verbose    Verbose output"
-    echo "  -n|--dry-run    Do a dry run, only prints what actions would be taken"
     echo "  -h|--help       Print this help"
+    echo "  -n|--dry-run    Do a dry run, only prints what actions would be taken"
+    echo "  -v|--verbose    Verbose output"
     echo
     echo "Options passed on to nix build"
     echo
@@ -29,8 +35,16 @@ function doHelp() {
     echo
     echo "Commands"
     echo
+    echo "  generations     Show all generations"
+    echo
     echo "  help            Print this help"
+    echo
+    echo "  rollback        Rollback and activate configuration"
+    echo
     echo "  switch          Build and activate configuration"
+    echo
+    echo "  switch-generation NUM"
+    echo "                  Switch generation and activate configuration"
 }
 
 function doSwitch() {
@@ -55,15 +69,29 @@ function doSwitch() {
     "${generationDir}/activate"
 }
 
+function doSwitchGeneration() {
+    local generationNum=$1
+
+    if [[ -x "${PROFILE_DIRECTORY}-${generationNum}-link/activate" ]]; then
+        echo "Run activation script..."
+        "${PROFILE_DIRECTORY}-${generationNum}-link/activate"
+    else
+        errorEcho "Activation was not successful, generation is either broken or already garbage collected."
+        errorEcho "See nix-on-droid generations for available generations."
+        exit 1
+    fi
+}
+
 
 COMMAND=
+COMMAND_ARGS=()
 PASSTHROUGH_OPTS=()
 
 while [[ $# -gt 0 ]]; do
     opt="$1"
     shift
     case $opt in
-        help|switch)
+        generations|help|rollback|switch|switch-generation)
             COMMAND="$opt"
             ;;
         -h|--help)
@@ -87,10 +115,17 @@ while [[ $# -gt 0 ]]; do
         -v|--verbose)
             export VERBOSE=1
             ;;
-        *)
-            errorEcho "$0: unknown option '$opt'"
-            errorEcho "Run '$0 --help' for usage help"
-            exit 1
+            *)
+                case $COMMAND in
+                    switch-generation)
+                        COMMAND_ARGS+=("$opt")
+                        ;;
+                    *)
+                        errorEcho "$0: unknown option '$opt'"
+                        errorEcho "Run '$0 --help' for usage help"
+                        exit 1
+                        ;;
+                esac
             ;;
     esac
 done
@@ -101,12 +136,31 @@ if [[ -z $COMMAND ]]; then
 fi
 
 case $COMMAND in
-    switch)
-        doSwitch
+    generations)
+        doGenerations
         ;;
     help)
         doHelp
         ;;
+    rollback)
+        if [[ $(readlink $PROFILE_DIRECTORY) =~ ^nix-on-droid-([0-9]+)-link$ ]]; then
+            doSwitchGeneration $((${BASH_REMATCH[1]} - 1))
+        else
+            errorEcho "nix-on-droid profile link is broken, please run nix-on-droid switch to fix it."
+            exit 1
+        fi
+        ;;
+    switch)
+        doSwitch
+        ;;
+    switch-generation)
+        if [[ ${#COMMAND_ARGS[@]} -eq 1 ]]; then
+            doSwitchGeneration ${COMMAND_ARGS[0]}
+        else
+            errorEcho "switch-generation expects one argument, got ${#COMMAND_ARGS[@]}."
+            exit 1
+        fi
+        ;;
     *)
         errorEcho "Unknown command: $COMMAND"
         doHelp >&2