populate: add passage source type

Update README.md to fix broken link with infos to the `target` attribute

README.md

@@ -1,12 +1,13 @@
-# krops (krebs ops)
+# krops (krebs operations)
 
-krops is a lightweigt toolkit to deploy NixOS systems, remotely or locally.
+krops is a lightweight toolkit to deploy NixOS systems, remotely or locally.
 
 
 ## Some Features
 
 - store your secrets in [password store](https://www.passwordstore.org/)
-- build your system remotely
+                     or [passage](https://github.com/FiloSottile/passage)
+- build your systems remotely
 - minimal overhead (it's basically just `nixos-rebuild switch`!)
 - run from custom nixpkgs branch/checkout/fork
 
@@ -15,12 +16,12 @@ krops is a lightweigt toolkit to deploy NixOS systems, remotely or locally.
 
 Create a file named `krops.nix` (name doesn't matter) with following content:
 
-```
+```nix
 let
   krops = (import <nixpkgs> {}).fetchgit {
     url = https://cgit.krebsco.de/krops/;
-    rev = "3022582ade8049e6ccf18f358cedb996d6716945";
-    sha256 = "0k3zhv2830z4bljcdvf6ciwjihk2zzcn9y23p49c6sba5hbsd6jb";
+    rev = "v1.25.0";
+    sha256 = "07mg3iaqjf1w49vmwfchi7b1w55bh7rvsbgicp2m47gnj9alwdb6";
   };
 
   lib = import "${krops}/lib";
@@ -52,11 +53,175 @@ in
 ```
 
 and run `$(nix-build --no-out-link krops.nix)` to deploy the target machine.
+krops exports some funtions under `krops.` namely:
 
-Under the hood, this will make the sources available on the target machine
+## writeDeploy
+
+This will make the sources available on the target machine
 below `/var/src`, and execute `nixos-rebuild switch -I /var/src`.
 
 
+### `target`
+
+The `target` attribute to `writeDeploy` can either be a string or an attribute
+set, specifying where to make the sources available, as well as where to run
+the deployment.
+
+If specified as string, the format could be described as:
+```
+[[USER]@]HOST[:PORT][/SOME/PATH]
+```
+
+Portions in square brackets are optional.
+
+If the `USER` is the empty string, as in e.g. `@somehost`, then the username
+will be obtained by ssh from its configuration files.
+
+If the `target` attribute is an attribute set, then it can specify the
+attributes `extraOptions`, `host`, `path`, `port`, `sudo`, and `user`.
+The `extraOptions` is a list of strings that get passed to ssh as additional
+arguments.  The `sudo` attribute is a boolean and if set to true, then it's
+possible to to deploy to targets that disallow sshing in as root, but allow
+(preferably passwordless) sudo.
+Example:
+
+```nix
+pkgs.krops.writeDeploy "deploy" {
+  source = /* ... */;
+  target = lib.mkTarget "user@host/path" // {
+    extraOptions = [
+      "-o" "LogLevel=DEBUG"
+    ];
+    sudo = true;
+  };
+}
+```
+For more details about the `target` attribute, please check the `mkTarget`
+function in [lib/default.nix](lib/default.nix).
+
+### `backup` (optional, defaults to false)
+
+Backup all paths specified in source before syncing new sources.
+
+### `buildTarget` (optional)
+
+If set the evaluation and build of the system will be executed on this host.
+`buildTarget` takes the same arguments as target.
+Sources will be synced to both `buildTarget` and `target`.
+Built packages will be uploaded from the `buildTarget` to `target` directly
+This requires the building machine to have ssh access to the target.
+To build the system on the same machine, that runs the krops command,
+set up a local ssh service and set the build host to localhost.
+
+### `crossDeploy` (optional, defaults to false)
+
+Use this option if target host architecture is not the same as the build host
+architecture as set by `buildHost` i.e. deploying to aarch64 from a x86_64
+machine. Setting this option will disable building & running nix in the wrong
+architecture when running `nixos-rebuild` on the deploying machine. It is
+required to set `nixpkgs.localSystem.system` in the NixOS configuration to the
+architecture of the target host. This option is only useful if the build host
+also has remote builders that are capable of producing artifacts for the deploy
+architecture.
+
+### `fast` (optional, defaults to false)
+
+Run `nixos-rebuild` immediately without building the system in a dedicated `nix
+build` step.
+
+### `force` (optional, defaults to false)
+
+Create the sentinel file (`/var/src/.populate`) before syncing the new source.
+
+### `operation` (optional, defaults to "switch")
+
+Specifies which `nixos-rebuild` operation to perform.
+
+### `useNixOutputMonitor` (optional, defaults to `"opportunistic"`)
+
+Specifies when to pipe `nixos-rebuild`'s output to
+[nom](https://github.com/maralorn/nix-output-monitor).
+
+Supported values:
+
+* `"opportunistic"` (default) -
+  Use `nom` only if it is present on the target machine.
+
+* `"optimistic"` -
+  Use `nom`, assuming it is present on the target machine.
+
+* `"pessimistic"` -
+  Use `nom` via `nix-shell` on the target machine.
+
+* `true` -
+  Use `nom`.
+  If it is not present on the target machine, then use it via `nix-shell`.
+
+* `false` -
+  Don't use `nom`
+
+## writeTest
+
+Very similiar to writeDeploy, but just builds the system on the target without
+activating it.
+
+This basically makes the sources available on the target machine
+below `/var/src`, and executes `NIX_PATH=/var/src nix-build -A system '<nixpkgs/nixos>'`.
+
+### `target`
+
+[see `writeDeploy`](#writeDeploy)
+
+### `backup` (optional, defaults to false)
+
+[see `writeDeploy`](#writeDeploy)
+
+### `force` (optional, defaults to false)
+
+[see `writeDeploy`](#writeDeploy)
+
+### `trace` (optional, defaults to false)
+
+run nix-build with `--show-trace`
+
+## writeCommand
+
+This can be used to run other commands than `nixos-rebuild` or pre/post build hooks.
+
+### `command`
+
+A function which takes the targetPath as an attribute.
+Example to activate/deactivate a swapfile before/after build:
+
+```nix
+pkgs.krops.writeCommand "deploy-with-swap" {
+  source = source;
+  target = "root@YOUR_IP_ADDRESS_OR_HOST_NAME_HERE";
+  command = targetPath: ''
+    swapon /var/swapfile
+    nixos-rebuild -I ${targetPath} switch
+    swapoff /var/swapfile
+  '';
+}
+```
+
+### `target`
+
+[see `writeDeploy`](#writeDeploy)
+
+### `backup` (optional, defaults to false)
+
+[see `writeDeploy`](#writeDeploy)
+
+### `force` (optional, defaults to false)
+
+[see `writeDeploy`](#writeDeploy)
+
+### `allocateTTY` (optional, defaults to false)
+
+whether the ssh session should do a pseudo-terminal allocation.
+sets `-t` on the ssh command.
+
 ## Source Types
 
 ### `derivation`
@@ -77,13 +242,28 @@ using [`rsync`](https://rsync.samba.org/).
 Supported attributes:
 
 * `path` -
-  absolute path to files that should by transfered
+  absolute path to files that should by transferred.
 
 * `useChecksum` (optional) -
   boolean that controls whether file contents should be checked to decide
   whether a file has changed.  This is useful when `path` points at files
   with mangled timestamps, e.g. the Nix store.
 
+  The default value is `true` if `path` is a derivation, and `false` otherwise.
+
+* `filters` (optional)
+  List of filters that should be passed to [`rsync`](https://rsync.samba.org/).
+  Filters are specified as attribute sets with the attributes `type` and
+  `pattern`.  Supported filter types are `include` and `exclude`.
+  Checkout the filter rules section in the
+  [rsync manual](https://download.samba.org/pub/rsync/rsync.html)
+  for further information.
+
+* `deleteExcluded` (optional)
+  boolean that controls whether the excluded directories should be deleted
+  if they exist on the target. This is passed to the `--delete-excluded` option
+  of rsync. Defaults to `true`.
+
 
 ### `git`
 
@@ -100,6 +280,10 @@ Supported attributes:
 * `clean.exclude` -
   List of patterns that should be excluded from Git cleaning.
 
+* `shallow` (optional)
+  boolean that controls whether only the requested commit ref. should be fetched
+  instead of the whole history, to save disk space and bandwith. Defaults to `false`.
+
 
 ### `pass`
 
@@ -115,6 +299,29 @@ Supported attributes:
   sub-directory in the password store.
 
 
+### `passage`
+
+The passage source type decrypts files from a local
+[passage store](https://github.com/FiloSottile/passage)
+and transfers them to the target using
+[`rsync`](https://rsync.samba.org/).
+
+Supported attributes:
+
+* `dir` -
+  Path to the passage store.
+  For a partial transfer, this may point to a subdirectory.
+  Example: `~/.passage/store/hosts/MYHOSTNAME`
+
+* `identities_file` (optional) -
+  Path to the identities file.
+  Defaults to `~/.passage/identities`.
+
+* `age` (optional) -
+  Path of the age binary.
+  Defaults to `age` (absolute path gets resolved using `passage`'s search path.)
+
+
 ### `pipe`
 
 Executes a local command, capture its stdout, and send that as a file to the
@@ -143,8 +350,9 @@ Supported attributes:
 
 ## Communication
 
-Comments, questions, pull-requests, etc. are very welcome, and can be directed
+Comments, questions, pull-requests and patches, etc. are very welcome, and can be directed
 at:
 
-- IRC: #krebs at freenode
+- IRC: #krebs at hackint
 - Mail: [spam@krebsco.de](mailto:spam@krebsco.de)
+- Github: https://github.com/krebs/krops/

ci.nix

@@ -5,7 +5,7 @@ let
   pkgs = import "${krops}/pkgs" {};
 
   source = lib.evalSource [{
-    nixos-config.file = toString (pkgs.writeText "nixos-config" ''
+    nixos-config.file = pkgs.writeText "nixos-config" ''
       { pkgs, ... }: {
 
         fileSystems."/" = { device = "/dev/sda1"; };
@@ -13,7 +13,7 @@ let
         services.openssh.enable = true;
         environment.systemPackages = [ pkgs.git ];
       }
-    '');
+    '';
     nixpkgs.symlink = toString <nixpkgs>;
   }];
 in {

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1689940971,
+        "narHash": "sha256-397xShPnFqPC59Bmpo3lS+/Aw0yoDRMACGo1+h2VJMo=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9ca785644d067445a4aa749902b29ccef61f7476",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,29 @@
+{
+  description = "krops - krebs operations";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs, ... }:
+    let
+      supportedSystems = [
+        "x86_64-linux"
+        "i686-linux"
+        "aarch64-linux"
+        "riscv64-linux"
+      ];
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+    in
+    {
+      lib = forAllSystems (system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+          krops = pkgs.callPackage ./pkgs/krops {};
+          populate = pkgs.callPackage ./pkgs/populate {};
+        in {
+          inherit populate;
+          inherit (krops) rebuild runShell withNixOutputMonitor writeCommand writeDeploy writeTest;
+        });
+    };
+}

lib/default.nix

@@ -28,13 +28,23 @@ let {
       # This function's return value can be used as pkgs.populate input.
       source: sanitize (eval source).config.source;
 
-    getHostName = let
+    maybeHostName = default: let
       # We're parsing /etc/hostname here because reading
       # /proc/sys/kernel/hostname yields ""
-      y = lib.filter lib.types.label.check (lib.splitString "\n" (lib.readFile /etc/hostname));
+      path = "/etc/hostname";
+      lines = lib.splitString "\n" (lib.readFile path);
+      hostNames = lib.filter lib.types.label.check lines;
     in
-      if lib.length y != 1 then throw "malformed /etc/hostname" else
-      lib.elemAt y 0;
+      if lib.pathExists path then
+        if lib.length hostNames == 1 then
+          lib.head hostNames
+        else
+          lib.trace "malformed ${path}" default
+      else
+        default;
+
+    firstWord = s:
+      lib.head (lib.match "^([^[:space:]]*).*" s);
 
     isLocalTarget = let
       origin = lib.mkTarget "";
@@ -43,15 +53,26 @@ let {
       lib.elem target.host [origin.host "localhost"];
 
     mkTarget = s: let
-      default = defVal: val: if val != null then val else defVal;
-      parse = lib.match "(([^@]+)@)?(([^:/]+))?(:([^/]+))?(/.*)?" s;
+      parse = lib.match "(([^@]*)@)?(([^:/]+))?(:([^/]+))?(/.*)?" s;
       elemAt' = xs: i: if lib.length xs > i then lib.elemAt xs i else null;
+      filterNull = lib.filterAttrs (n: v: v != null);
     in {
-      user = default (lib.getEnv "LOGNAME") (elemAt' parse 1);
-      host = default (lib.maybeEnv "HOSTNAME" lib.getHostName) (elemAt' parse 3);
-      port = default "22" /* "ssh"? */ (elemAt' parse 5);
-      path = default "/var/src" /* no default? */ (elemAt' parse 6);
-    };
+      user = lib.maybeEnv "LOGNAME" null;
+      host = lib.maybeEnv "HOSTNAME" (lib.maybeHostName "localhost");
+      port = null;
+      path = "/var/src";
+      sudo = false;
+      extraOptions = [];
+    } // (if lib.isString s then filterNull {
+      user = elemAt' parse 1;
+      host = elemAt' parse 3;
+      port = elemAt' parse 5;
+      path = elemAt' parse 6;
+    } else s);
+
+    mkUserPortSSHOpts = target:
+      (lib.optionals (target.user != null) ["-l" target.user]) ++
+      (lib.optionals (target.port != null) ["-p" target.port]);
 
     shell = let
       isSafeChar = lib.testString "[-+./0-9:=A-Z_a-z]";

lib/types/populate.nix

@@ -21,11 +21,15 @@
       };
       file = lib.mkOption {
         apply = x:
-          if lib.types.absolute-pathname.check x
+          if lib.types.absolute-pathname.check x || lib.types.package.check x
             then { path = x; }
             else x;
         default = null;
-        type = lib.types.nullOr (lib.types.either lib.types.absolute-pathname source-types.file);
+        type = lib.types.nullOr (lib.types.oneOf [
+          lib.types.absolute-pathname
+          lib.types.package
+          source-types.file
+        ]);
       };
       git = lib.mkOption {
         default = null;
@@ -35,6 +39,17 @@
         default = null;
         type = lib.types.nullOr source-types.pass;
       };
+      passage = lib.mkOption {
+        apply = x:
+          if lib.types.pathname.check x
+            then { dir = x; }
+            else x;
+        default = null;
+        type = lib.types.nullOr (lib.types.oneOf [
+          lib.types.pathname
+          source-types.passage
+        ]);
+      };
       pipe = lib.mkOption {
         apply = x:
           if lib.types.absolute-pathname.check x
@@ -54,6 +69,18 @@
     };
   });
 
+  filter = lib.types.submodule {
+    options = {
+      type = lib.mkOption {
+        type = lib.types.enum ["include" "exclude"];
+        default = "exclude";
+      };
+      pattern = lib.mkOption {
+        type = lib.types.str;
+      };
+    };
+  };
+
   source-types = {
     derivation = lib.types.submodule {
       options = {
@@ -71,6 +98,43 @@
           default = false;
           type = lib.types.bool;
         };
+        exclude = lib.mkOption {
+          apply = x:
+            if x != [] then
+              lib.warn
+                "file.*.exclude is deprecated in favor of file.*.filters"
+                x
+            else
+              x;
+          description = ''
+            DEPRECATED, use `filters`.
+          '';
+          type = lib.types.listOf lib.types.str;
+          default = [];
+          example = [".git"];
+        };
+        filters = lib.mkOption {
+          type = lib.types.listOf filter;
+          default = [];
+          example = [
+            {
+              type = "include";
+              pattern = "*.nix";
+            }
+            {
+              type = "include";
+              pattern = "*/";
+            }
+            {
+              type = "exclude";
+              pattern = "*";
+            }
+          ];
+        };
+        deleteExcluded = lib.mkOption {
+          default = true;
+          type = lib.types.bool;
+        };
       };
     };
     git = lib.types.submodule {
@@ -81,12 +145,20 @@
             type = lib.types.listOf lib.types.str;
           };
         };
+        fetchAlways = lib.mkOption {
+          type = lib.types.bool;
+          default = false;
+        };
         ref = lib.mkOption {
           type = lib.types.str; # TODO lib.types.git.ref
         };
         url = lib.mkOption {
           type = lib.types.str; # TODO lib.types.git.url
         };
+        shallow = lib.mkOption {
+          default = false;
+          type = lib.types.bool;
+        };
       };
     };
     pass = lib.types.submodule {
@@ -99,6 +171,21 @@
         };
       };
     };
+    passage = lib.types.submodule {
+      options = {
+        age = lib.mkOption {
+          default = "age";
+          type = lib.types.pathname;
+        };
+        dir = lib.mkOption {
+          type = lib.types.pathname;
+        };
+        identities_file = lib.mkOption {
+          default = toString ~/.passage/identities;
+          type = lib.types.pathname;
+        };
+      };
+    };
     pipe = lib.types.submodule {
       options = {
         command = lib.mkOption {

pkgs/default.nix

@@ -1,15 +1,7 @@
 { overlays ? [], ... }@args:
 
-let
-  nix-writers = builtins.fetchGit {
-    url = https://cgit.krebsco.de/nix-writers/;
-    rev = "c528cf970e292790b414b4c1c8c8e9d7e73b2a71";
-  };
-in
-
 import <nixpkgs> (args // {
-  overlays = overlays ++ [
+  overlays = [
     (import ./overlay.nix)
-    (import "${nix-writers}/pkgs")
-  ];
+  ] ++ overlays;
 })

pkgs/krops/default.nix

@@ -2,64 +2,145 @@ let
   lib = import ../../lib;
 in
 
-{ exec, nix, openssh, populate, writeDash }: rec {
+{ nix, openssh, populate, writers }: rec {
 
-  build = target:
-    exec "rebuild.${target.host}" rec {
-      filename = "${openssh}/bin/ssh";
-      argv = [
-        filename
-        "-l" target.user
-        "-p" target.port
-        "-t"
-        target.host
-        (lib.concatStringsSep " " [
-          "nix build"
-          "-I ${lib.escapeShellArg target.path}"
-          "--no-link -f '<nixpkgs/nixos>'"
-          "config.system.build.toplevel"
-        ])
-      ];
-    };
+  rebuild = {
+    useNixOutputMonitor
+  }:
+  args: target:
+    runShell target {}
+      (withNixOutputMonitor target useNixOutputMonitor /* sh */ ''
+        NIX_PATH=${lib.escapeShellArg target.path} \
+        nixos-rebuild ${lib.escapeShellArgs args}
+      '');
 
-  rebuild = args: target:
-    exec "rebuild.${target.host}" rec {
-      filename = "${openssh}/bin/ssh";
-      argv = [
-        filename
-        "-l" target.user
-        "-p" target.port
-        target.host
-        "nixos-rebuild -I ${lib.escapeShellArg target.path} ${
-          lib.concatMapStringsSep " " lib.escapeShellArg args
-        }"
-      ];
-    };
+  runShell = target: {
+    allocateTTY ? false
+  }: command:
+    let
+      command' = /* sh */ ''
+        ${lib.optionalString target.sudo "sudo"} \
+        /bin/sh -c ${lib.escapeShellArg command}
+      '';
+    in
+      if lib.isLocalTarget target
+      then command'
+      else
+        writers.writeDash "krops.${target.host}.${lib.firstWord command}" ''
+          exec ${openssh}/bin/ssh ${lib.escapeShellArgs (lib.flatten [
+            (lib.mkUserPortSSHOpts target)
+            (if allocateTTY then "-t" else "-T")
+            target.extraOptions
+            target.host
+            command'
+          ])}
+        '';
 
-  writeDeploy = name: { force ? false, source, target }: let
+  withNixOutputMonitor = target: mode_: command: let
+    mode =
+      lib.getAttr (lib.typeOf mode_)  {
+        bool = lib.toJSON mode_;
+        string = mode_;
+      };
+  in /* sh */ ''
+    printf '# use nix-output-monitor: %s\n' ${lib.escapeShellArg mode} >&2
+    ${lib.getAttr mode rec {
+      opportunistic = /* sh */ ''
+        if command -v nom >/dev/null; then
+          ${optimistic}
+        else
+          ${false}
+        fi
+      '';
+      optimistic = /* sh */ ''
+        (${command}) 2>&1 | nom
+      '';
+      pessimistic = /* sh */ ''
+        NIX_PATH=${lib.escapeShellArg target.path} \
+        nix-shell -p nix-output-monitor --run ${lib.escapeShellArg optimistic}
+      '';
+      true = /* sh */ ''
+        if command -v nom >/dev/null; then
+          ${optimistic}
+        else
+          ${pessimistic}
+        fi
+      '';
+      false = command;
+    }}
+  '';
+
+  writeCommand = name: {
+    command ? (targetPath: "echo ${targetPath}"),
+    backup ? false,
+    force ? false,
+    allocateTTY ? false,
+    source,
+    target
+  }: let
     target' = lib.mkTarget target;
   in
-    writeDash name ''
+    writers.writeDash name ''
       set -efu
-      ${populate { inherit force source; target = target'; }}
-      ${build target'}
-      ${rebuild ["switch"] target'}
+      ${populate { inherit backup force source; target = target'; }}
+      ${runShell target' { inherit allocateTTY; } (command target'.path)}
     '';
 
-  writeTest = name: { force ? false, source, target }: let
+  writeDeploy = name: {
+    backup ? false,
+    buildTarget ? null,
+    crossDeploy ? false,
+    fast ? null,
+    force ? false,
+    operation ? "switch",
+    source,
+    target,
+    useNixOutputMonitor ? "opportunistic"
+  }: let
+    buildTarget' =
+      if buildTarget == null
+        then target'
+        else lib.mkTarget buildTarget;
+    target' = lib.mkTarget target;
+  in
+    lib.traceIf (fast != null) "writeDeploy: it's now always fast, setting the `fast` attribute is deprecated and will be removed in future" (
+      writers.writeDash name ''
+        set -efu
+        ${lib.optionalString (buildTarget' != target')
+          (populate { inherit backup force source; target = buildTarget'; })}
+        ${populate { inherit backup force source; target = target'; }}
+        ${rebuild { inherit useNixOutputMonitor; } ([
+          operation
+        ] ++ lib.optionals crossDeploy [
+          "--no-build-nix"
+        ] ++ lib.optionals (buildTarget' != target') [
+          "--build-host" "${buildTarget'.user}@${buildTarget'.host}"
+          "--target-host" "${target'.user}@${target'.host}"
+        ] ++ lib.optionals target'.sudo [
+          "--use-remote-sudo"
+        ]) buildTarget'}
+      ''
+    );
+
+  writeTest = name: {
+    backup ? false,
+    force ? false,
+    source,
+    target,
+    trace ? false
+  }: let
     target' = lib.mkTarget target;
   in
     assert lib.isLocalTarget target';
-    writeDash name ''
+    writers.writeDash name ''
       set -efu
-      ${populate { inherit force source; target = target'; }} >&2
+      ${populate { inherit backup force source; target = target'; }} >&2
       NIX_PATH=${lib.escapeShellArg target'.path} \
       ${nix}/bin/nix-build \
           -A system \
           --keep-going \
           --no-out-link \
-          --show-trace \
+          ${lib.optionalString trace "--show-trace"} \
           '<nixpkgs/nixos>'
     '';
-
 }

pkgs/populate/default.nix

@@ -1,17 +1,17 @@
 with import ../../lib;
 with shell;
 
-{ coreutils, dash, findutils, git, jq, openssh, pass, rsync, writeDash }:
+{ coreutils, dash, findutils, git, jq, openssh, pass, passage, rsync, writers }:
 
 let
   check = { force, target }: let
     sentinelFile = "${target.path}/.populate";
-  in shell' target /* sh */ ''
+  in runShell target /* sh */ ''
     ${optionalString force /* sh */ ''
       mkdir -vp ${quote (dirOf sentinelFile)} >&2
       touch ${quote sentinelFile}
     ''}
-    if ! test -f ${quote sentinelFile}; then
+    if ! test -e ${quote sentinelFile}; then
       >&2 printf 'error: missing sentinel file: %s\n' ${quote (
         optionalString (!isLocalTarget target) "${target.host}:" +
         sentinelFile
@@ -20,20 +20,60 @@ let
     fi
   '';
 
-  pop.derivation = target: source: shell' target /* sh */ ''
+  do-backup = { target }: let
+    sentinelFile = "${target.path}/.populate";
+  in
+    runShell target /* sh */ ''
+      if ! test -d ${quote sentinelFile}; then
+        >&2 printf 'error" sentinel file is not a directory: %s\n' ${quote (
+          optionalString (!isLocalTarget target) "${target.host}:" +
+          sentinelFile
+        )}
+        exit 1
+      fi
+      rsync >&2 \
+          -aAXF \
+          --delete \
+          --exclude /.populate \
+          --link-dest=${quote target.path} \
+          ${target.path}/ \
+          ${target.path}/.populate/backup/
+    '';
+
+  pop.derivation = target: source: runShell target /* sh */ ''
     nix-build -E ${quote source.text} -o ${quote target.path} >&2
   '';
 
   pop.file = target: source: let
-    configAttrs = ["useChecksum"];
-    config = filterAttrs (name: _: elem name configAttrs) source;
+    config = rsyncDefaultConfig // derivedConfig // sourceConfig;
+    derivedConfig = {
+      useChecksum =
+        if isStorePath source.path
+          then true
+          else rsyncDefaultConfig.useChecksum;
+    };
+    sourceConfig =
+      filterAttrs (name: _: elem name (attrNames rsyncDefaultConfig)) source;
+    sourcePath =
+      if isStorePath source.path
+        then quote (toString source.path)
+        else quote source.path;
   in
-    rsync' target config (quote source.path);
+    rsync' target config sourcePath;
 
-  pop.git = target: source: shell' target /* sh */ ''
+  pop.git = target: source: runShell target /* sh */ ''
     set -efu
+    # Remove target path if it doesn't look like a git worktree.
+    # This can happen e.g. when it had a different type earlier.
+    if ! test -e ${quote target.path}/.git; then
+      rm -fR ${quote target.path}
+    fi
     if ! test -e ${quote target.path}; then
-      git clone --recurse-submodules ${quote source.url} ${quote target.path}
+      ${if source.shallow then /* sh */ ''
+        git init ${quote target.path}
+      '' else /* sh */ ''
+        git clone --recurse-submodules ${quote source.url} ${quote target.path}
+      ''}
     fi
     cd ${quote target.path}
     if ! url=$(git config remote.origin.url); then
@@ -46,9 +86,21 @@ let
     hash=${quote source.ref}
 
     if ! test "$(git log --format=%H -1)" = "$hash"; then
-      if ! git log -1 "$hash" >/dev/null 2>&1; then
-        git fetch origin
-      fi
+      ${if source.fetchAlways then /* sh */ ''
+        ${if source.shallow then /* sh */ ''
+          git fetch --depth=1 origin "$hash"
+        '' else /* sh */ ''
+          git fetch origin
+        ''}
+      '' else /* sh */ ''
+        if ! git log -1 "$hash" >/dev/null 2>&1; then
+          ${if source.shallow then /* sh */ ''
+            git fetch --depth=1 origin "$hash"
+          '' else /* sh */ ''
+            git fetch origin
+          ''}
+        fi
+      ''}
       git reset --hard "$hash" >&2
       git submodule update --init --recursive
     fi
@@ -67,8 +119,16 @@ let
     umask 0077
 
     if test -e ${quote source.dir}/.git; then
-      local_pass_info=${quote source.name}\ $(${git}/bin/git -C ${quote source.dir} log -1 --format=%H ${quote source.name})
-      remote_pass_info=$(${shell' target /* sh */ ''
+      local_pass_info=${quote source.name}\ $(
+        ${git}/bin/git -C ${quote source.dir} log -1 --format=%H ${quote source.name}
+        # we append a hash for every symlink, otherwise we would miss updates on
+        # files where the symlink points to
+        ${findutils}/bin/find ${quote source.dir}/${quote source.name} -type l \
+            -exec ${coreutils}/bin/realpath {} + |
+          ${coreutils}/bin/sort |
+          ${findutils}/bin/xargs -r -n 1 ${git}/bin/git -C ${quote source.dir} log -1 --format=%H
+      )
+      remote_pass_info=$(${runShell target /* sh */ ''
         cat ${quote target.path}/.pass_info || :
       ''})
 
@@ -83,45 +143,80 @@ let
       rm -fR "$tmp_dir"
     }
 
-    ${findutils}/bin/find ${quote passPrefix} -type f |
+    ${findutils}/bin/find ${quote passPrefix} -type f -follow ! -name .gpg-id |
     while read -r gpg_path; do
 
       rel_name=''${gpg_path#${quote passPrefix}}
       rel_name=''${rel_name%.gpg}
 
       pass_date=$(
-        ${git}/bin/git -C ${quote source.dir} log -1 --format=%aI "$gpg_path"
+        if test -e ${quote source.dir}/.git; then
+          ${git}/bin/git -C ${quote source.dir} log -1 --format=%aI "$gpg_path"
+        fi
       )
       pass_name=${quote source.name}/$rel_name
       tmp_path=$tmp_dir/$rel_name
 
       ${coreutils}/bin/mkdir -p "$(${coreutils}/bin/dirname "$tmp_path")"
       PASSWORD_STORE_DIR=${quote source.dir} ${pass}/bin/pass show "$pass_name" > "$tmp_path"
-      ${coreutils}/bin/touch -d "$pass_date" "$tmp_path"
+      if [ -n "$pass_date" ]; then
+        ${coreutils}/bin/touch -d "$pass_date" "$tmp_path"
+      fi
     done
 
     if test -n "''${local_pass_info-}"; then
       echo "$local_pass_info" > "$tmp_dir"/.pass_info
     fi
 
-    ${rsync' target {} /* sh */ "$tmp_dir"}
+    ${rsync' target rsyncDefaultConfig /* sh */ "$tmp_dir"}
+  '';
+
+  pop.passage = target: source: /* sh */ ''
+    set -efu
+
+    export PASSAGE_AGE=${quote source.age}
+    export PASSAGE_DIR=${quote source.dir}
+    export PASSAGE_IDENTITIES_FILE=${quote source.identities_file}
+
+    umask 0077
+
+    tmp_dir=$(${coreutils}/bin/mktemp -dt populate-passage.XXXXXXXX)
+    trap cleanup EXIT
+    cleanup() {
+      rm -fR "$tmp_dir"
+    }
+
+    ${findutils}/bin/find "$PASSAGE_DIR" -type f -name \*.age -follow |
+    while read -r age_path; do
+
+      rel_name=''${age_path#$PASSAGE_DIR}
+      rel_name=''${rel_name%.age}
+
+      tmp_path=$tmp_dir/$rel_name
+
+      ${coreutils}/bin/mkdir -p "$(${coreutils}/bin/dirname "$tmp_path")"
+      ${passage}/bin/passage show "$rel_name" > "$tmp_path"
+      ${coreutils}/bin/touch -r "$age_path" "$tmp_path"
+    done
+
+    ${rsync' target rsyncDefaultConfig /* sh */ "$tmp_dir"}
   '';
 
   pop.pipe = target: source: /* sh */ ''
     ${quote source.command} | {
-      ${shell' target /* sh */ "cat > ${quote target.path}"}
+      ${runShell target /* sh */ "cat > ${quote target.path}"}
     }
   '';
 
   # TODO rm -fR instead of ln -f?
-  pop.symlink = target: source: shell' target /* sh */ ''
+  pop.symlink = target: source: runShell target /* sh */ ''
     ln -fnsT ${quote source.target} ${quote target.path}
   '';
 
   populate = target: name: source: let
     source' = source.${source.type};
     target' = target // { path = "${target.path}/${name}"; };
-  in writeDash "populate.${target'.host}.${name}" ''
+  in writers.writeDash "populate.${target'.host}.${name}" ''
     set -efu
     ${pop.${source.type} target' source'}
   '';
@@ -132,39 +227,59 @@ let
       source_path=$source_path/
     fi
     ${rsync}/bin/rsync \
-        ${optionalString (config.useChecksum or false) /* sh */ "--checksum"} \
+        ${optionalString config.useChecksum /* sh */ "--checksum"} \
+        ${optionalString target.sudo /* sh */ "--rsync-path=\"sudo rsync\""} \
+        ${concatMapStringsSep " "
+          (pattern: /* sh */ "--exclude ${quote pattern}")
+          config.exclude} \
+        ${concatMapStringsSep " "
+          (filter: /* sh */ "--${filter.type} ${quote filter.pattern}")
+          config.filters} \
         -e ${quote (ssh' target)} \
         -vFrlptD \
-        --delete-excluded \
+        ${optionalString config.deleteExcluded /* sh */ "--delete-excluded"} \
         "$source_path" \
         ${quote (
-          optionalString (!isLocalTarget target)
-                         "${target.user}@${target.host}:" +
+          optionalString (!isLocalTarget target) (
+            (optionalString (target.user != "") "${target.user}@") +
+            "${target.host}:"
+          ) +
           target.path
         )} \
       >&2
   '';
 
-  shell' = target: script:
-    if isLocalTarget target
-      then script
-      else /* sh */ ''
-        ${ssh' target} ${quote target.host} ${quote script}
-      '';
+  rsyncDefaultConfig = {
+    useChecksum = false;
+    exclude = [];
+    filters = [];
+    deleteExcluded = true;
+  };
 
-  ssh' = target: concatMapStringsSep " " quote [
+  runShell = target: command:
+    if isLocalTarget target
+      then command
+      else
+        if target.sudo then /* sh */ ''
+          ${ssh' target} ${quote target.host} ${quote "sudo bash -c ${quote command}"}
+        '' else ''
+          ${ssh' target} ${quote target.host} ${quote command}
+        '';
+
+  ssh' = target: concatMapStringsSep " " quote (flatten [
     "${openssh}/bin/ssh"
-    "-l" target.user
-    "-o" "ControlPersist=no"
-    "-p" target.port
+    (mkUserPortSSHOpts target)
     "-T"
-  ];
+    target.extraOptions
+  ]);
 
 in
 
-{ force ? false, source, target }: writeDash "populate.${target.host}" ''
+{ backup ? false, force ? false, source, target }:
+writers.writeDash "populate.${target.host}" ''
   set -efu
   ${check { inherit force target; }}
   set -x
+  ${optionalString backup (do-backup { inherit target; })}
   ${concatStringsSep "\n" (mapAttrsToList (populate target) source)}
 ''