libstore: Add LocalDerivationGoal prepareSandbox hook

Add a new OS-specific hook called `prepareSandbox`, run before forking
On Darwin this is empty as nothing is required,
on Linux this creates the chroot directory and adds basic files,
and on platforms using a fallback this throws an exception

Change-Id: Ie30c38c387f2e0e5844b2afa32fd4d33b1180dae

1 files changed, 17 insertions, 0 deletions

diff --git a/src/libstore/build/local-derivation-goal.hh b/src/libstore/build/local-derivation-goal.hh
index 91329ca35..857339b5d 100644
--- a/src/libstore/build/local-derivation-goal.hh
+++ b/src/libstore/build/local-derivation-goal.hh
@@ -325,11 +325,28 @@ protected:
     using DerivationGoal::DerivationGoal;
 
     /**
+     * Setup dependencies outside the sandbox.
+     * Called in the parent nix process.
+     */
+    virtual void prepareSandbox()
+    {
+        throw Error("sandboxing builds is not supported on this platform");
+    };
+
+    /**
      * Execute the builder, replacing the current process.
      * Generally this means an `execve` call.
      */
     virtual void execBuilder(std::string builder, Strings args, Strings envStrs);
 
+    /**
+     * Whether derivation can be built on current platform with `uid-range` feature
+     */
+    virtual bool supportsUidRange()
+    {
+        return false;
+    }
+
 };
 
 }