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Add external builders

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These are helper programs that execute derivations for specified
system types (e.g. using QEMU to emulate another system type).

To use, set `external-builders`:

  external-builders = [{"systems": ["aarch64-linux"], "program": "/path/to/external-builder.py"}]

The external builder gets one command line argument, the path to a JSON file containing all necessary information about the derivation:

  {
    "args": [...],
    "builder": "/nix/store/kwcyvgdg98n98hqapaz8sw92pc2s78x6-bash-5.2p37/bin/bash",
    "env": {
      "HOME": "/homeless-shelter",
      ...
    },
    "realStoreDir": "/tmp/nix/nix/store",
    "storeDir": "/nix/store",
    "tmpDir": "/tmp/nix-shell.dzQ2hE/nix-build-patchelf-0.14.3.drv-46/build",
    "tmpDirInSandbox": "/build"
  }

Co-authored-by: Cole Helbling <cole.helbling@determinate.systems>
This commit is contained in:
Eelco Dolstra 2025-10-03 14:34:13 +02:00
parent 76ac3758d7
commit 584ef0ffd3
6 changed files with 274 additions and 18 deletions
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43
src/libstore/unix/build/derivation-builder.cc
View file

@ -229,6 +229,12 @@ protected:
return acquireUserLock(1, false);
}
/**
* Throw an exception if we can't do this derivation because of
* missing system features.
*/
virtual void checkSystem();
/**
* Return the paths that should be made available in the sandbox.
* This includes:
@ -666,21 +672,8 @@ static bool checkNotWorldWritable(std::filesystem::path path)
return true;
}
std::optional<Descriptor> DerivationBuilderImpl::startBuild()
void DerivationBuilderImpl::checkSystem()
{
if (useBuildUsers()) {
if (!buildUser)
buildUser = getBuildUser();
if (!buildUser)
return std::nullopt;
}
/* Make sure that no other processes are executing under the
sandbox uids. This must be done before any chownToBuilder()
calls. */
prepareUser();
/* Right platform? */
if (!drvOptions.canBuildLocally(store, drv)) {
auto msg =
@ -704,6 +697,24 @@ std::optional<Descriptor> DerivationBuilderImpl::startBuild()
throw BuildError(BuildResult::Failure::InputRejected, msg);
}
}
std::optional<Descriptor> DerivationBuilderImpl::startBuild()
{
if (useBuildUsers()) {
if (!buildUser)
buildUser = getBuildUser();
if (!buildUser)
return std::nullopt;
}
checkSystem();
/* Make sure that no other processes are executing under the
sandbox uids. This must be done before any chownToBuilder()
calls. */
prepareUser();
auto buildDir = store.config->getBuildDir();
@ -1909,12 +1920,16 @@ StorePath DerivationBuilderImpl::makeFallbackPath(const StorePath & path)
#include "chroot-derivation-builder.cc"
#include "linux-derivation-builder.cc"
#include "darwin-derivation-builder.cc"
#include "external-derivation-builder.cc"
namespace nix {
std::unique_ptr<DerivationBuilder> makeDerivationBuilder(
LocalStore & store, std::unique_ptr<DerivationBuilderCallbacks> miscMethods, DerivationBuilderParams params)
{
if (auto builder = ExternalDerivationBuilder::newIfSupported(store, miscMethods, params))
return builder;
bool useSandbox = false;
/* Are we doing a sandboxed build? */