External derivation builders #14145
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External derivation builders #14145
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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 <[email protected]>
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Mic92
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Oct 5, 2025
Mic92
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Oct 5, 2025
| Setting<ExternalBuilders> externalBuilders{ | ||
| this, | ||
| {}, | ||
| "external-builders", |
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This is a privileged nix option, right?
Mic92
reviewed
Oct 5, 2025
| std::unique_ptr<DerivationBuilder> makeDerivationBuilder( | ||
| LocalStore & store, std::unique_ptr<DerivationBuilderCallbacks> miscMethods, DerivationBuilderParams params) | ||
| { | ||
| if (auto builder = ExternalDerivationBuilder::newIfSupported(store, miscMethods, params)) |
There was a problem hiding this comment.
Does this filter out builtin derivations?
Mic92
reviewed
Oct 5, 2025
| "/nix/store/vj1c3wf9…-source-stdenv.sh", | ||
| "/nix/store/shkw4qm9…-default-builder.sh" | ||
| ], | ||
| "builder": "/nix/store/s1qkj0ph…-bash-5.2p37/bin/bash", |
There was a problem hiding this comment.
The following are not needed?
"inputDrvs": {
"ag533xlxphzj8nh4y9wsksf057fgsls0-hello-2.12.2.tar.gz.drv": {
"dynamicOutputs": {},
"outputs": [
"out"
]
},
"j3aid0i43g57xkf4z9fbiqcbb4ljb06r-stdenv-darwin.drv": {
"dynamicOutputs": {},
"outputs": [
"out"
]
},
"pmlwjrsjfdk5r9j1mw97hm3pj0mc8lqk-version-check-hook.drv": {
"dynamicOutputs": {},
"outputs": [
"out"
]
},
"sbx1ghn3g6vaad1i8m730zbdsa3m9lyv-bash-5.3p3.drv": {
"dynamicOutputs": {},
"outputs": [
"out"
]
}
},
"inputSrcs": [
"l622p70vy8k5sh7y5wizi5f2mic6ynpg-source-stdenv.sh",
"shkw4qm9qcw5sc5n1k5jznc83ny02r39-default-builder.sh"
],
xokdvium
reviewed
Oct 5, 2025
Comment on lines
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to
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| for (auto & i : drv.args) | ||
| l.push_back(rewriteStrings(i, inputRewrites)); | ||
| json.emplace("args", std::move(l)); | ||
| } | ||
| { | ||
| auto j = nlohmann::json::object(); | ||
| for (auto & [name, value] : env) | ||
| j.emplace(name, rewriteStrings(value, inputRewrites)); | ||
| json.emplace("env", std::move(j)); | ||
| } |
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Wouldn't it make sense to reuse the existing shored-up JSON derivation format @Ericson2314 has worked on?
xokdvium
reviewed
Oct 5, 2025
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| pid = startProcess([&]() { | ||
| openSlave(); | ||
| try { | ||
| commonChildInit(); | ||
|
|
||
| Strings args = {externalBuilder.program}; |
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Considering that this will be run in the daemon would it be prudent to start dropping capabilities before executing the child?
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Motivation
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: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" }Context
Upstreamed from Determinate Nix (DeterminateSystems#78). This is the mechanism that allows doing Linux builds on macOS.
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