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Simplify the handling of the hash modulo

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Rather than having four different but very similar types of hashes, make
only one, with a tag indicating whether it corresponds to a regular of
deferred derivation.

This implies a slight logical change: The original Nix+multiple-outputs
model assumed only one hash-modulo per derivation. Adding
multiple-outputs CA derivations changed this as these have one
hash-modulo per output. This change is now treating each derivation as
having one hash modulo per output.
This obviously means that we internally loose the guaranty that
all the outputs of input-addressed derivations have the same hash
modulo. But it turns out that it doesn’t matter because there’s nothing
in the code taking advantage of that fact (and it probably shouldn’t
anyways).

The upside is that it is now much easier to work with these hashes, and
we can get rid of a lot of useless `std::visit{ overloaded`.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>
This commit is contained in:
Théophane Hufschmitt 2022-03-16 14:21:09 +01:00
parent 2d572a250f
commit 390269ed87
5 changed files with 56 additions and 118 deletions
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77
src/libstore/derivations.cc
View file

@ -474,7 +474,7 @@ Sync<DrvHashes> drvHashes;
/* Look up the derivation by value and memoize the
`hashDerivationModulo` call.
*/
static const DrvHashModulo pathDerivationModulo(Store & store, const StorePath & drvPath)
static const DrvHash pathDerivationModulo(Store & store, const StorePath & drvPath)
{
{
auto hashes = drvHashes.lock();
@ -509,7 +509,7 @@ static const DrvHashModulo pathDerivationModulo(Store & store, const StorePath &
don't leak the provenance of fixed outputs, reducing pointless cache
misses as the build itself won't know this.
*/
DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs)
DrvHash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs)
{
auto type = drv.type();
@ -524,7 +524,10 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
+ store.printStorePath(dof.path(store, drv.name, i.first)));
outputHashes.insert_or_assign(i.first, std::move(hash));
}
return outputHashes;
return DrvHash{
.hashes = outputHashes,
.kind = DrvHash::Kind::Regular,
};
}
auto kind = std::visit(overloaded {
@ -540,65 +543,36 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
},
}, drv.type().raw());
/* For other derivations, replace the inputs paths with recursive
calls to this function. */
std::map<std::string, StringSet> inputs2;
for (auto & [drvPath, inputOutputs0] : drv.inputDrvs) {
// Avoid lambda capture restriction with standard / Clang
auto & inputOutputs = inputOutputs0;
const auto & res = pathDerivationModulo(store, drvPath);
std::visit(overloaded {
// Regular non-CA derivation, replace derivation
[&](const DrvHash & drvHash) {
kind |= drvHash.kind;
inputs2.insert_or_assign(drvHash.hash.to_string(Base16, false), inputOutputs);
},
// CA derivation's output hashes
[&](const CaOutputHashes & outputHashes) {
std::set<std::string> justOut = { "out" };
for (auto & output : inputOutputs) {
/* Put each one in with a single "out" output.. */
const auto h = outputHashes.at(output);
inputs2.insert_or_assign(
h.to_string(Base16, false),
justOut);
}
},
}, res.raw());
if (res.kind == DrvHash::Kind::Deferred)
kind = DrvHash::Kind::Deferred;
for (auto & outputName : inputOutputs) {
const auto h = res.hashes.at(outputName);
inputs2[h.to_string(Base16, false)].insert(outputName);
}
}
auto hash = hashString(htSHA256, drv.unparse(store, maskOutputs, &inputs2));
return DrvHash { .hash = hash, .kind = kind };
}
void operator |= (DrvHash::Kind & self, const DrvHash::Kind & other) noexcept
{
switch (other) {
case DrvHash::Kind::Regular:
break;
case DrvHash::Kind::Deferred:
self = other;
break;
std::map<std::string, Hash> outputHashes;
for (const auto & [outputName, _] : drv.outputs) {
outputHashes.insert_or_assign(outputName, hash);
}
return DrvHash {
.hashes = outputHashes,
.kind = kind,
};
}
std::map<std::string, Hash> staticOutputHashes(Store & store, const Derivation & drv)
{
std::map<std::string, Hash> res;
std::visit(overloaded {
[&](const DrvHash & drvHash) {
for (auto & outputName : drv.outputNames()) {
res.insert({outputName, drvHash.hash});
}
},
[&](const CaOutputHashes & outputHashes) {
res = outputHashes;
},
}, hashDerivationModulo(store, drv, true).raw());
return res;
return hashDerivationModulo(store, drv, true).hashes;
}
@ -747,7 +721,7 @@ static void rewriteDerivation(Store & store, BasicDerivation & drv, const String
auto hashModulo = hashDerivationModulo(store, Derivation(drv), true);
for (auto & [outputName, output] : drv.outputs) {
if (std::holds_alternative<DerivationOutput::Deferred>(output.raw())) {
auto & h = hashModulo.requireNoFixedNonDeferred();
auto & h = hashModulo.hashes.at(outputName);
auto outPath = store.makeOutputPath(outputName, h, drv.name);
drv.env[outputName] = store.printStorePath(outPath);
output = DerivationOutput::InputAddressed {
@ -758,13 +732,6 @@ static void rewriteDerivation(Store & store, BasicDerivation & drv, const String
}
const Hash & DrvHashModulo::requireNoFixedNonDeferred() const {
auto * drvHashOpt = std::get_if<DrvHash>(&raw());
assert(drvHashOpt);
assert(drvHashOpt->kind == DrvHash::Kind::Regular);
return drvHashOpt->hash;
}
static bool tryResolveInput(
Store & store, StorePathSet & inputSrcs, StringMap & inputRewrites,
const StorePath & inputDrv, const StringSet & inputOutputs)