diff --git a/doc/manual/src/language/advanced-attributes.md b/doc/manual/src/language/advanced-attributes.md index 5e8aaeba0..86f0f24b5 100644 --- a/doc/manual/src/language/advanced-attributes.md +++ b/doc/manual/src/language/advanced-attributes.md @@ -229,6 +229,8 @@ Derivations can declare some infrequently used optional attributes. [`outputHashAlgo`](#adv-attr-outputHashAlgo) like for *fixed-output derivations* (see above). + It also implicitly requires that the machine to build the derivation must have the `ca-derivations` [system feature](@docroot@/command-ref/conf-file.md#conf-system-features). + - [`passAsFile`]{#adv-attr-passAsFile}\ A list of names of attributes that should be passed via files rather than environment variables. For example, if you have @@ -335,3 +337,15 @@ Derivations can declare some infrequently used optional attributes. This is useful, for example, when generating self-contained filesystem images with their own embedded Nix store: hashes found inside such an image refer to the embedded store and not to the host's Nix store. + +- [`requiredSystemFeatures`]{#adv-attr-requiredSystemFeatures}\ + + If a derivation has the `requiredSystemFeatures` attribute, then Nix will only build it on a machine that has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features). + + For example, setting + + ```nix + requiredSystemFeatures = [ "kvm" ]; + ``` + + ensures that the derivation can only be built on a machine with the `kvm` feature. diff --git a/doc/manual/src/release-notes/rl-2.12.md b/doc/manual/src/release-notes/rl-2.12.md index e2045d7bf..e1e3efe1a 100644 --- a/doc/manual/src/release-notes/rl-2.12.md +++ b/doc/manual/src/release-notes/rl-2.12.md @@ -2,7 +2,6 @@ * On Linux, Nix can now run builds in a user namespace where they run as root (UID 0) and have 65,536 UIDs available. - This is primarily useful for running containers such as `systemd-nspawn` inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn]. diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh index cf10edebd..0569f43b9 100644 --- a/src/libstore/globals.hh +++ b/src/libstore/globals.hh @@ -343,7 +343,7 @@ public: users in `build-users-group`. UIDs are allocated starting at 872415232 (0x34000000) on Linux and 56930 on macOS. - )"}; + )", {}, true, Xp::AutoAllocateUids}; Setting startId{this, #if __linux__ @@ -697,19 +697,40 @@ public: getDefaultSystemFeatures(), "system-features", R"( - A set of system “features” supported by this machine, e.g. `kvm`. - Derivations can express a dependency on such features through the - derivation attribute `requiredSystemFeatures`. For example, the - attribute + A set of system “features” supported by this machine. - requiredSystemFeatures = [ "kvm" ]; + This complements the [`system`](#conf-system) and [`extra-platforms`](#conf-extra-platforms) configuration options and the corresponding [`system`](@docroot@/language/derivations.md#attr-system) attribute on derivations. - ensures that the derivation can only be built on a machine with the - `kvm` feature. + A derivation can require system features in the [`requiredSystemFeatures` attribute](@docroot@/language/advanced-attributes.md#adv-attr-requiredSystemFeatures), and the machine to build the derivation must have them. - This setting by default includes `kvm` if `/dev/kvm` is accessible, - and the pseudo-features `nixos-test`, `benchmark` and `big-parallel` - that are used in Nixpkgs to route builds to specific machines. + System features are user-defined, but Nix sets the following defaults: + + - `kvm` + + Included by default if `/dev/kvm` is accessible. + + - `nixos-test`, `benchmark`, `big-parallel` + + These historical pseudo-features are always enabled for backwards compatibility, as they are used in Nixpkgs to route Hydra builds to specific machines. + + - `ca-derivations` + + Included by default if the [`ca-derivations` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-ca-derivations) is enabled. + + This system feature is implicitly required by derivations with the [`__contentAddressed` attribute](@docroot@/language/advanced-attributes.md#adv-attr-__contentAddressed). + + - `recursive-nix` + + Included by default if the [`recursive-nix` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-recursive-nix) is enabled. + + - `uid-range` + + On Linux, Nix can run builds in a user namespace where they run as root (UID 0) and have 65,536 UIDs available. + This is primarily useful for running containers such as `systemd-nspawn` inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn]. + + [nspawn]: https://github.com/NixOS/nix/blob/67bcb99700a0da1395fa063d7c6586740b304598/tests/systemd-nspawn.nix. + + Included by default on Linux if the [`auto-allocate-uids`](#conf-auto-allocate-uids) setting is enabled. )", {}, false}; Setting substituters{ diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh index da1a3eefb..4e233bac3 100644 --- a/src/libstore/store-api.hh +++ b/src/libstore/store-api.hh @@ -153,19 +153,22 @@ struct StoreConfig : public Config Setting priority{this, 0, "priority", R"( - Priority of this store when used as a substituter. A lower value means a higher priority. + Priority of this store when used as a [substituter](@docroot@/command-ref/conf-file.md#conf-substituters). + A lower value means a higher priority. )"}; Setting wantMassQuery{this, false, "want-mass-query", R"( - Whether this store (when used as a substituter) can be - queried efficiently for path validity. + Whether this store can be queried efficiently for path validity when used as a [substituter](@docroot@/command-ref/conf-file.md#conf-substituters). )"}; Setting systemFeatures{this, getDefaultSystemFeatures(), "system-features", - "Optional features that the system this store builds on implements (like \"kvm\")."}; + R"( + Optional [system features](@docroot@/command-ref/conf-file.md#conf-system-features) available on the system this store uses to build derivations. + Example: `"kvm"` + )" }; }; class Store : public std::enable_shared_from_this, public virtual StoreConfig