libstore: extract env and args rewriting from child

this really doesn't have to be here, it doesn't help very much. doing it
in the parent is cheap enough to not care and sandbox setup is not async
yet *anyway*, so we would not even notice if the old way was any faster.

Change-Id: I5a3a99af0fa5928e9a42f9c6589d98ff38b8c775

lix/libstore/build/local-derivation-goal.cc

@@ -860,8 +860,23 @@ try {
         setupConfiguredCertificateAuthority();
     }
 
+    /* Fill in the environment. */
+    Strings envStrs;
+    for (auto & i : env) {
+        envStrs.push_back(rewriteStrings(i.first + "=" + i.second, inputRewrites));
+    }
+
+    /* Fill in the arguments. */
+    Strings args;
+
+    args.push_back(std::string(baseNameOf(drv->builder)));
+
+    for (auto & i : drv->args) {
+        args.push_back(rewriteStrings(i, inputRewrites));
+    }
+
     /* Fork a child to build the package. */
-    pid = startChild(netrcData, caFileData, std::move(builderOut));
+    pid = startChild(netrcData, caFileData, envStrs, args, std::move(builderOut));
 
     /* parent */
     pid.setSeparatePG(true);
@@ -900,6 +915,8 @@ try {
 Pid LocalDerivationGoal::startChild(
     const std::optional<std::string> & netrcData,
     const std::optional<std::string> & caFileData,
+    const Strings & envStrs,
+    const Strings & args,
     AutoCloseFD logPTY
 )
 {
@@ -908,7 +925,7 @@ Pid LocalDerivationGoal::startChild(
             throw SysError("failed to redirect build output to log file");
         }
         closeOnExec(STDERR_FILENO, false);
-        runChild(netrcData, caFileData);
+        runChild(netrcData, caFileData, envStrs, args);
     });
 }
 
@@ -1144,7 +1161,10 @@ void LocalDerivationGoal::chownToBuilder(const AutoCloseFD & fd)
 }
 
 void LocalDerivationGoal::runChild(
-    const std::optional<std::string> & netrcData, const std::optional<std::string> & caFileData
+    const std::optional<std::string> & netrcData,
+    const std::optional<std::string> & caFileData,
+    const Strings & envStrs,
+    const Strings & args
 )
 {
     /* Warning: in the child we should absolutely not make any SQLite
@@ -1174,11 +1194,6 @@ void LocalDerivationGoal::runChild(
 
         // FIXME: set other limits to deterministic values?
 
-        /* Fill in the environment. */
-        Strings envStrs;
-        for (auto & i : env)
-            envStrs.push_back(rewriteStrings(i.first + "=" + i.second, inputRewrites));
-
         /* If we are running in `build-users' mode, then switch to the
            user we allocated above.  Make sure that we drop all root
            privileges.  Note that above we have closed all file
@@ -1205,14 +1220,6 @@ void LocalDerivationGoal::runChild(
 
         finishChildSetup();
 
-        /* Fill in the arguments. */
-        Strings args;
-
-        args.push_back(std::string(baseNameOf(drv->builder)));
-
-        for (auto & i : drv->args)
-            args.push_back(rewriteStrings(i, inputRewrites));
-
         /* Indicate that we managed to set up the build environment. */
         writeFull(STDERR_FILENO, std::string("\2\n"));
 

lix/libstore/build/local-derivation-goal.hh

@@ -214,8 +214,12 @@ struct LocalDerivationGoal : public DerivationGoal
     /**
      * Run the builder's process.
      */
-    void
-    runChild(const std::optional<std::string> & netrcData, const std::optional<std::string> & caFileData);
+    void runChild(
+        const std::optional<std::string> & netrcData,
+        const std::optional<std::string> & caFileData,
+        const Strings & envStrs,
+        const Strings & args
+    );
 
     /**
      * Check that the derivation outputs all exist and register them
@@ -315,6 +319,8 @@ protected:
     virtual Pid startChild(
         const std::optional<std::string> & netrcData,
         const std::optional<std::string> & caFileData,
+        const Strings & envStrs,
+        const Strings & args,
         AutoCloseFD logPTY
     );
 

lix/libstore/platform/linux.cc

@@ -1241,6 +1241,8 @@ bool LinuxLocalDerivationGoal::prepareChildSetup()
 Pid LinuxLocalDerivationGoal::startChild(
     const std::optional<std::string> & netrcData,
     const std::optional<std::string> & caFileData,
+    const Strings & envStrs,
+    const Strings & args,
     AutoCloseFD logPTY
 )
 {
@@ -1253,7 +1255,7 @@ Pid LinuxLocalDerivationGoal::startChild(
 
     // If we're not sandboxing no need to faff about, use the fallback
     if (!useChroot) {
-        return LocalDerivationGoal::startChild(netrcData, caFileData, std::move(logPTY));
+        return LocalDerivationGoal::startChild(netrcData, caFileData, envStrs, args, std::move(logPTY));
     }
     /* Set up private namespaces for the build:
 
@@ -1329,7 +1331,8 @@ Pid LinuxLocalDerivationGoal::startChild(
             options.cloneFlags |= CLONE_NEWUSER;
         }
 
-        pid_t child = startProcess([&]() { runChild(netrcData, caFileData); }, options).release();
+        pid_t child =
+            startProcess([&]() { runChild(netrcData, caFileData, envStrs, args); }, options).release();
 
         writeFull(sendPid.writeSide.get(), fmt("%d\n", child));
         _exit(0);

lix/libstore/platform/linux.hh

@@ -76,6 +76,8 @@ private:
     Pid startChild(
         const std::optional<std::string> & netrcData,
         const std::optional<std::string> & caFileData,
+        const Strings & envStrs,
+        const Strings & args,
         AutoCloseFD logPTY
     ) override;