nix: configure sharefs via fileSystems

Turns out this did not work because in the vm test harness, virtualisation.fileSystems completely and silently overrides fileSystems, causing its contents to not even be evaluated anymore. This is not documented as far as I can tell, and is not obvious by any stretch of the imagination. The current hack is cargo culted from nix-community/impermanence and hopefully lasts until this project fully replaces nix.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/sharefs/test/configuration.nix

@@ -1,4 +1,4 @@
-{ pkgs, config, ... }:
+{ pkgs, ... }:
 {
   users.users = {
     alice = {
@@ -17,9 +17,6 @@
   environment = {
     # For benchmarking sharefs:
     systemPackages = [ pkgs.fsmark ];
-
-    # For sharefs option checks without adding to PATH:
-    etc.sharefs.source = "${config.environment.hakurei.package}/libexec/sharefs";
   };
 
   virtualisation = {

cmd/sharefs/test/test.py

@@ -2,14 +2,14 @@ start_all()
 machine.wait_for_unit("multi-user.target")
 
 # To check sharefs version:
-print(machine.succeed("/etc/sharefs -V"))
+print(machine.succeed("sharefs -V"))
 
-# Make sure sharefs did not terminate:
-machine.wait_for_unit("sharefs.service")
+# Make sure sharefs started:
+machine.wait_for_unit("sdcard.mount")
 
 machine.succeed("mkdir /mnt")
 def check_bad_opts_output(opts, want, source="/etc", privileged=False):
-    output = machine.fail(("" if privileged else "sudo -u alice -i ") + f"/etc/sharefs -f -o source={source},{opts} /mnt 2>&1")
+    output = machine.fail(("" if privileged else "sudo -u alice -i ") + f"sharefs -f -o source={source},{opts} /mnt 2>&1")
     if output != want:
         raise Exception(f"unexpected output: {output}")
 
@@ -40,7 +40,7 @@ machine.succeed("rmdir /mnt")
 
 # Unprivileged mount/unmount:
 machine.succeed("sudo -u alice -i mkdir /home/alice/{sdcard,persistent}")
-machine.succeed("sudo -u alice -i /etc/sharefs -o source=/home/alice/persistent /home/alice/sdcard")
+machine.succeed("sudo -u alice -i sharefs -o source=/home/alice/persistent /home/alice/sdcard")
 machine.succeed("sudo -u alice -i touch /home/alice/sdcard/check")
 machine.succeed("sudo -u alice -i umount /home/alice/sdcard")
 machine.succeed("sudo -u alice -i rm /home/alice/persistent/check")

flake.nix

@@ -138,6 +138,10 @@
               ;
           };
           hsu = pkgs.callPackage ./cmd/hsu/package.nix { inherit (self.packages.${system}) hakurei; };
+          sharefs = pkgs.linkFarm "sharefs" {
+            "bin/sharefs" = "${hakurei}/libexec/sharefs";
+            "bin/mount.fuse.sharefs" = "${hakurei}/libexec/sharefs";
+          };
 
           dist = pkgs.runCommand "${hakurei.name}-dist" { buildInputs = hakurei.targetPkgs ++ [ pkgs.pkgsStatic.musl ]; } ''
             # go requires XDG_CACHE_HOME for the build cache

nixos.nix

@@ -24,11 +24,38 @@ let
   getsubuid = userid: appid: userid * 100000 + 10000 + appid;
   getsubname = userid: appid: "u${toString userid}_a${toString appid}";
   getsubhome = userid: appid: "${cfg.stateDir}/u${toString userid}/a${toString appid}";
+
+  mountpoints = {
+    ${cfg.sharefs.name} = mkIf (cfg.sharefs.source != null) {
+      depends = [ cfg.sharefs.source ];
+      device = "sharefs";
+      fsType = "fuse.sharefs";
+      noCheck = true;
+      options = [
+        "rw"
+        "noexec"
+        "nosuid"
+        "nodev"
+        "noatime"
+        "allow_other"
+        "mkdir"
+        "source=${cfg.sharefs.source}"
+        "setuid=${toString config.users.users.${cfg.sharefs.user}.uid}"
+        "setgid=${toString config.users.groups.${cfg.sharefs.group}.gid}"
+      ];
+    };
+  };
 in
 
 {
   imports = [ (import ./options.nix packages) ];
 
+  options = {
+    # Forward declare a dummy option for VM filesystems since the real one won't exist
+    # unless the VM module is actually imported.
+    virtualisation.fileSystems = lib.mkOption { };
+  };
+
   config = mkIf cfg.enable {
     assertions = [
       (
@@ -66,38 +93,9 @@ in
       ) "" cfg.users;
     };
 
-    systemd.services = {
-      sharefs = mkIf (cfg.sharefs.source != null) {
-        unitConfig.RequiresMountsFor = cfg.sharefs.source;
-        serviceConfig = {
-          NoNewPrivileges = true;
-        };
-        script = ''
-          ${pkgs.coreutils}/bin/install -dm0 ${cfg.sharefs.name}
-
-          exec ${cfg.package}/libexec/sharefs -f \
-            -o ${
-              lib.join "," [
-                "noexec"
-                "nosuid"
-                "nodev"
-                "noatime"
-                "auto_unmount"
-                "allow_other"
-                "setuid=$(id -u ${cfg.sharefs.user})"
-                "setgid=$(id -g ${cfg.sharefs.group})"
-                "source=${cfg.sharefs.source}"
-                "mkdir"
-              ]
-            } ${cfg.sharefs.name}
-        '';
-
-        # do not unmount on configuration changes
-        restartIfChanged = false;
-
-        wantedBy = [ "multi-user.target" ];
-      };
-    };
+    environment.systemPackages = optional (cfg.sharefs.source != null) cfg.sharefs.package;
+    fileSystems = mountpoints;
+    virtualisation.fileSystems = mountpoints;
 
     home-manager =
       let

options.md

@@ -809,6 +809,96 @@ package
 
 
 
+## environment\.hakurei\.sharefs\.package
+
+
+
+The sharefs package to use\.
+
+
+
+*Type:*
+package
+
+
+
+*Default:*
+` <derivation sharefs> `
+
+
+
+## environment\.hakurei\.sharefs\.group
+
+
+
+Name of the group to run the sharefs daemon as\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "sharefs" `
+
+
+
+## environment\.hakurei\.sharefs\.name
+
+
+
+Host path to mount sharefs on\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "/sdcard" `
+
+
+
+## environment\.hakurei\.sharefs\.source
+
+
+
+Writable backing directory\. Setting this to null disables sharefs\.
+
+
+
+*Type:*
+null or string
+
+
+
+*Default:*
+` null `
+
+
+
+## environment\.hakurei\.sharefs\.user
+
+
+
+Name of the user to run the sharefs daemon as\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "sharefs" `
+
+
+
 ## environment\.hakurei\.shell
 
 

options.nix

@@ -41,6 +41,12 @@ in
       };
 
       sharefs = {
+        package = mkOption {
+          type = types.package;
+          default = packages.${pkgs.stdenv.hostPlatform.system}.sharefs;
+          description = "The sharefs package to use.";
+        };
+
         user = mkOption {
           type = types.str;
           default = "sharefs";