nixpkgs/nixos/lib/eval-config.nix

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# From an end-user configuration file (`configuration.nix'), build a NixOS
# configuration object (`config') from which we can retrieve option
# values.
# !!! Please think twice before adding to this argument list!
# Ideally eval-config.nix would be an extremely thin wrapper
# around lib.evalModules, so that modular systems that have nixos configs
# as subcomponents (e.g. the container feature, or nixops if network
# expressions are ever made modular at the top level) can just use
# types.submodule instead of using eval-config.nix
evalConfigArgs@
{ # !!! system can be set modularly, would be nice to remove
system ? builtins.currentSystem
, # !!! is this argument needed any more? The pkgs argument can
# be set modularly anyway.
pkgs ? null
, # !!! what do we gain by making this configurable?
baseModules ? import ../modules/module-list.nix
, # !!! See comment about args in lib/modules.nix
extraArgs ? {}
, # !!! See comment about args in lib/modules.nix
specialArgs ? {}
, modules
, modulesLocation ? (builtins.unsafeGetAttrPos "modules" evalConfigArgs).file or null
, # !!! See comment about check in lib/modules.nix
check ? true
Add support for lightweight NixOS containers You can now say: systemd.containers.foo.config = { services.openssh.enable = true; services.openssh.ports = [ 2022 ]; users.extraUsers.root.openssh.authorizedKeys.keys = [ "ssh-dss ..." ]; }; which defines a NixOS instance with the given configuration running inside a lightweight container. You can also manage the configuration of the container independently from the host: systemd.containers.foo.path = "/nix/var/nix/profiles/containers/foo"; where "path" is a NixOS system profile. It can be created/updated by doing: $ nix-env --set -p /nix/var/nix/profiles/containers/foo \ -f '<nixos>' -A system -I nixos-config=foo.nix The container configuration (foo.nix) should define boot.isContainer = true; to optimise away the building of a kernel and initrd. This is done automatically when using the "config" route. On the host, a lightweight container appears as the service "container-<name>.service". The container is like a regular NixOS (virtual) machine, except that it doesn't have its own kernel. It has its own root file system (by default /var/lib/containers/<name>), but shares the Nix store of the host (as a read-only bind mount). It also has access to the network devices of the host. Currently, if the configuration of the container changes, running "nixos-rebuild switch" on the host will cause the container to be rebooted. In the future we may want to send some message to the container so that it can activate the new container configuration without rebooting. Containers are not perfectly isolated yet. In particular, the host's /sys/fs/cgroup is mounted (writable!) in the guest.
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, prefix ? []
, lib ? import ../../lib
, extraModules ? let e = builtins.getEnv "NIXOS_EXTRA_MODULE_PATH";
in if e == "" then [] else [(import e)]
}:
let pkgs_ = pkgs;
in
let
evalModulesMinimal = (import ./default.nix {
inherit lib;
# Implicit use of feature is noted in implementation.
featureFlags.minimalModules = { };
}).evalModules;
pkgsModule = rec {
_file = ./eval-config.nix;
key = _file;
config = {
# Explicit `nixpkgs.system` or `nixpkgs.localSystem` should override
# this. Since the latter defaults to the former, the former should
# default to the argument. That way this new default could propagate all
# they way through, but has the last priority behind everything else.
nixpkgs.system = lib.mkDefault system;
# Stash the value of the `system` argument. When using `nesting.children`
# we want to have the same default value behavior (immediately above)
# without any interference from the user's configuration.
nixpkgs.initialSystem = system;
_module.args.pkgs = lib.mkIf (pkgs_ != null) (lib.mkForce pkgs_);
};
};
withWarnings = x:
lib.warnIf (evalConfigArgs?extraArgs) "The extraArgs argument to eval-config.nix is deprecated. Please set config._module.args instead."
lib.warnIf (evalConfigArgs?check) "The check argument to eval-config.nix is deprecated. Please set config._module.check instead."
x;
legacyModules =
lib.optional (evalConfigArgs?extraArgs) {
config = {
_module.args = extraArgs;
};
}
++ lib.optional (evalConfigArgs?check) {
config = {
_module.check = lib.mkDefault check;
};
};
allUserModules =
let
# Add the invoking file (or specified modulesLocation) as error message location
# for modules that don't have their own locations; presumably inline modules.
locatedModules =
if modulesLocation == null then
modules
else
map (lib.setDefaultModuleLocation modulesLocation) modules;
in
locatedModules ++ legacyModules;
noUserModules = evalModulesMinimal ({
inherit prefix specialArgs;
modules = baseModules ++ extraModules ++ [ pkgsModule modulesModule ];
});
# Extra arguments that are useful for constructing a similar configuration.
modulesModule = {
config = {
_module.args = {
inherit noUserModules baseModules extraModules modules;
};
};
};
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nixosWithUserModules = noUserModules.extendModules { modules = allUserModules; };
in
withWarnings nixosWithUserModules // {
inherit extraArgs;
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inherit (nixosWithUserModules._module.args) pkgs;
}