From 5a49c5b9b12c305ed450a71ceb1a001585903a19 Mon Sep 17 00:00:00 2001
From: Alexey Rybalchenko <alexryba@gmail.com>
Date: Tue, 28 Apr 2020 19:17:47 +0200
Subject: [PATCH] Truncate the file used for the region mapping

---
 fairmq/shmem/Region.cxx | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fairmq/shmem/Region.cxx b/fairmq/shmem/Region.cxx
index 4259fee4..1132bb94 100644
--- a/fairmq/shmem/Region.cxx
+++ b/fairmq/shmem/Region.cxx
@@ -19,6 +19,7 @@
 
 #include <cerrno>
 #include <chrono>
+#include <ios>
 
 using namespace std;
 
@@ -49,7 +50,17 @@ Region::Region(Manager& manager, uint64_t id, uint64_t size, bool remote, Region
     if (path != "") {
         fName = string(path + fName);
 
-        fFile = fopen(fName.c_str(), fRemote ? "r+" : "w+");
+        if (!fRemote) {
+            // create a file
+            filebuf fbuf;
+            if (fbuf.open(fName, ios_base::in | ios_base::out | ios_base::trunc | ios_base::binary)) {
+                // set the size
+                fbuf.pubseekoff(size - 1, ios_base::beg);
+                fbuf.sputc(0);
+            }
+        }
+
+        fFile = fopen(fName.c_str(), "r+");
 
         if (!fFile) {
             LOG(error) << "Failed to initialize file: " << fName;