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unsafeDiscardReferences

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Adds a new boolean structured attribute
`outputChecks.<output>.unsafeDiscardReferences` which disables scanning
an output for runtime references.

    __structuredAttrs = true;
    outputChecks.out.unsafeDiscardReferences = true;

This is useful when creating filesystem images containing their own embedded Nix
store: they are self-contained blobs of data with no runtime dependencies.

Setting this attribute requires the experimental feature
`discard-references` to be enabled.
This commit is contained in:
Naïm Favier 2022-09-23 23:30:29 +02:00
parent 15341334b5
commit 15f7fa59be
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GPG key ID: 95AFCE8211908325
7 changed files with 58 additions and 7 deletions
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27
src/libstore/build/local-derivation-goal.cc
View file

@ -2319,11 +2319,30 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
buildUser ? std::optional(buildUser->getUIDRange()) : std::nullopt,
inodesSeen);
debug("scanning for references for output '%s' in temp location '%s'", outputName, actualPath);
bool discardReferences = false;
if (auto structuredAttrs = parsedDrv->getStructuredAttrs()) {
if (auto outputChecks = get(*structuredAttrs, "outputChecks")) {
if (auto output = get(*outputChecks, outputName)) {
if (auto unsafeDiscardReferences = get(*output, "unsafeDiscardReferences")) {
settings.requireExperimentalFeature(Xp::DiscardReferences);
if (!unsafeDiscardReferences->is_boolean())
throw Error("attribute 'outputChecks.\"%s\".unsafeDiscardReferences' of derivation '%s' must be a Boolean", outputName, drvPath.to_string());
discardReferences = unsafeDiscardReferences->get<bool>();
}
}
}
}
/* Pass blank Sink as we are not ready to hash data at this stage. */
NullSink blank;
auto references = scanForReferences(blank, actualPath, referenceablePaths);
StorePathSet references;
if (discardReferences)
debug("discarding references of output '%s'", outputName);
else {
debug("scanning for references for output '%s' in temp location '%s'", outputName, actualPath);
/* Pass blank Sink as we are not ready to hash data at this stage. */
NullSink blank;
references = scanForReferences(blank, actualPath, referenceablePaths);
}
outputReferencesIfUnregistered.insert_or_assign(
outputName,

1
src/libutil/experimental-features.cc
View file

@ -16,6 +16,7 @@ std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
{ Xp::ReplFlake, "repl-flake" },
{ Xp::AutoAllocateUids, "auto-allocate-uids" },
{ Xp::Cgroups, "cgroups" },
{ Xp::DiscardReferences, "discard-references" },
};
const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)

1
src/libutil/experimental-features.hh
View file

@ -25,6 +25,7 @@ enum struct ExperimentalFeature
ReplFlake,
AutoAllocateUids,
Cgroups,
DiscardReferences,
};
/**