zfs: respect canmount

Also refactor `zpool` type to use `zfs_fs` to construct the root dataset
for the zpool, which means we no longer need to duplicate the dataset
create and mount logic inside the `zpool` type.

lib/types/zfs_fs.nix

@@ -6,17 +6,27 @@
       default = config._module.args.name;
       description = "Name of the dataset";
     };
+
+    _name = lib.mkOption {
+      type = lib.types.str;
+      default = "${config._parent.name}/${config.name}";
+      internal = true;
+      description = "Fully quantified name for dataset";
+    };
+
     type = lib.mkOption {
       type = lib.types.enum [ "zfs_fs" ];
       default = "zfs_fs";
       internal = true;
       description = "Type";
     };
+
     options = lib.mkOption {
       type = lib.types.attrsOf lib.types.str;
       default = { };
       description = "Options to set for the dataset";
     };
+
     mountOptions = lib.mkOption {
       type = lib.types.listOf lib.types.str;
       default = [ "defaults" ];
@@ -33,6 +43,7 @@
       internal = true;
       default = parent;
     };
+
     _meta = lib.mkOption {
       internal = true;
       readOnly = true;
@@ -40,6 +51,7 @@
       default = _dev: { };
       description = "Metadata";
     };
+
     _create = diskoLib.mkCreateOption {
       inherit config options;
       # -u prevents mounting newly created datasets, which is
@@ -47,17 +59,18 @@
       # since (create order != mount order)
       # -p creates parents automatically
       default = ''
-        zfs create -up ${config._parent.name}/${config.name} \
+        zfs create -up ${config._name} \
           ${lib.concatStringsSep " " (lib.mapAttrsToList (n: v: "-o ${n}=${v}") config.options)}
       '';
-    };
+    } // { readOnly = false; };
+
     _mount = diskoLib.mkMountOption {
       inherit config options;
       default =
-        lib.optionalAttrs (config.options.mountpoint or "" != "none") {
+        lib.optionalAttrs (config.options.mountpoint or "" != "none" && config.options.canmount or "" != "off") {
           fs.${config.mountpoint} = ''
-            if ! findmnt ${config._parent.name}/${config.name} "${rootMountPoint}${config.mountpoint}" >/dev/null 2>&1; then
+            if ! findmnt ${config._name} "${rootMountPoint}${config.mountpoint}" >/dev/null 2>&1; then
-              mount ${config._parent.name}/${config.name} "${rootMountPoint}${config.mountpoint}" \
+              mount ${config._name} "${rootMountPoint}${config.mountpoint}" \
                 -o X-mount.mkdir \
                 ${lib.concatMapStringsSep " " (opt: "-o ${opt}") config.mountOptions} \
                 ${lib.optionalString ((config.options.mountpoint or "") != "legacy") "-o zfsutil"} \
@@ -66,19 +79,21 @@
           '';
         };
     };
+
     _config = lib.mkOption {
       internal = true;
       readOnly = true;
       default =
-        lib.optional (config.options.mountpoint or "" != "none") {
+        lib.optional (config.options.mountpoint or "" != "none" && config.options.canmount or "" != "off") {
           fileSystems.${config.mountpoint} = {
-            device = "${config._parent.name}/${config.name}";
+            device = "${config._name}";
             fsType = "zfs";
             options = config.mountOptions ++ lib.optional ((config.options.mountpoint or "") != "legacy") "zfsutil";
           };
         };
       description = "NixOS configuration";
     };
+
     _pkgs = lib.mkOption {
       internal = true;
       readOnly = true;

lib/types/zpool.nix

@@ -85,32 +85,13 @@
               zpool import -l -R ${rootMountPoint} '${config.name}'
             ${lib.concatMapStrings (x: x.dev or "") (lib.attrValues datasetMounts)}
           '';
-          fs = (datasetMounts.fs or { }) // lib.optionalAttrs (config.mountpoint != null) {
+          inherit (datasetMounts) fs;
-            ${config.mountpoint} = ''
-              if ! findmnt ${config.name} "${rootMountPoint}${config.mountpoint}" >/dev/null 2>&1; then
-                mount ${config.name} "${rootMountPoint}${config.mountpoint}" \
-                  ${lib.optionalString ((config.options.mountpoint or "") != "legacy") "-o zfsutil"} \
-                  ${lib.concatMapStringsSep " " (opt: "-o ${opt}") config.mountOptions} \
-                  -o X-mount.mkdir \
-                  -t zfs
-              fi
-            '';
-          };
         };
     };
     _config = lib.mkOption {
       internal = true;
       readOnly = true;
-      default = [
+      default = map (dataset: dataset._config) (lib.attrValues config.datasets);
-        (map (dataset: dataset._config) (lib.attrValues config.datasets))
-        (lib.optional (config.mountpoint != null) {
-          fileSystems.${config.mountpoint} = {
-            device = config.name;
-            fsType = "zfs";
-            options = config.mountOptions ++ lib.optional ((config.options.mountpoint or "") != "legacy") "zfsutil";
-          };
-        })
-      ];
       description = "NixOS configuration";
     };
     _pkgs = lib.mkOption {
@@ -121,4 +102,14 @@
       description = "Packages";
     };
   };
+
+  config = {
+    datasets."__root" = {
+      _name = config.name;
+      _create = "";
+      type = "zfs_fs";
+      mountpoint = config.mountpoint;
+      options = config.rootFsOptions;
+    };
+  };
 }