Merge pull request #8706 from fricklerhandwerk/doc-system-features

document system features
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Valentin Gagarin 2023-09-26 04:21:31 +02:00 committed by GitHub
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4 changed files with 53 additions and 16 deletions

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@ -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.

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@ -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.
<!-- FIXME: move this to its own section about system features -->
This is primarily useful for running containers such as `systemd-nspawn`
inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn].

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@ -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<uint32_t> 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<Strings> substituters{

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@ -153,19 +153,22 @@ struct StoreConfig : public Config
Setting<int> 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<bool> 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<StringSet> 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<Store>, public virtual StoreConfig