From d98755b0c291fed59c71957ac8dbe4ee94e58b10 Mon Sep 17 00:00:00 2001
From: Will Dietz <w@wdtz.org>
Date: Wed, 14 Mar 2018 21:39:01 -0500
Subject: [PATCH] nix-daemon: preserve errno in signal handler (thanks tsan)

---
 src/nix-daemon/nix-daemon.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 890bffa19..30e2b5455 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -816,8 +816,11 @@ static void processConnection(bool trusted)
 
 static void sigChldHandler(int sigNo)
 {
+    // Ensure we don't modify errno of whatever we've interrupted
+    auto saved_errno = errno;
     /* Reap all dead children. */
     while (waitpid(-1, 0, WNOHANG) > 0) ;
+    errno = saved_errno;
 }