From 885bebf13b619816c0196100accc312c86e0abdf Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Mon, 23 Feb 2015 15:52:04 +0100
Subject: [PATCH] More graceful fallback for chroots on Linux < 2.13

---
 src/libstore/build.cc | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index ac5ca7bc3..707c416d6 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1997,12 +1997,11 @@ void DerivationGoal::startBuilder()
             int flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | CLONE_NEWUTS | CLONE_PARENT | SIGCHLD;
             if (!fixedOutput) flags |= CLONE_NEWNET;
             pid_t child = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
-            if (child == -1) {
-                if (errno == EINVAL)
-                    throw SysError("cloning builder process (Linux chroot builds require 3.13 or later)");
-                else
-                    throw SysError("cloning builder process");
-            }
+            if (child == -1 && errno == EINVAL)
+                /* Fallback for Linux < 2.13 where CLONE_NEWPID and
+                   CLONE_PARENT are not allowed together. */
+                child = clone(childEntry, stack + sizeof(stack) - 8, flags & ~CLONE_NEWPID, this);
+            if (child == -1) throw SysError("cloning builder process");
             writeFull(builderOut.writeSide, int2String(child) + "\n");
             _exit(0);
         });