From 76df06ff8fa39ae0cb0d167b7f622139778dc7d7 Mon Sep 17 00:00:00 2001
From: Kamil Dudka <kdudka@redhat.com>
Date: Thu, 4 Jan 2018 09:42:10 +0100
Subject: [PATCH] mv -n: do not overwrite the destination

... if it is created by another process after mv has checked its
non-existence.

* src/copy.c (copy_internal): Use renameat2 (..., RENAME_NOREPLACE)
if called by mv -n.  If it fails with EEXIST in that case, pretend
successful rename as if the existing destination file was detected
by the preceding lstat call.

Fixes https://bugs.gnu.org/29961
---
 src/copy.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/copy.c b/src/copy.c
index 2a804945e..be4e357a8 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -53,6 +53,7 @@
 #include "ignore-value.h"
 #include "ioblksize.h"
 #include "quote.h"
+#include "renameat2.h"
 #include "root-uid.h"
 #include "same.h"
 #include "savedir.h"
@@ -2319,7 +2320,12 @@ copy_internal (char const *src_name, char const *dst_name,
 
   if (x->move_mode)
     {
-      if (rename (src_name, dst_name) == 0)
+      int flags = 0;
+      if (x->interactive == I_ALWAYS_NO)
+        /* do not replace DST_NAME if it was created since our last check */
+        flags = RENAME_NOREPLACE;
+
+      if (renameat2 (AT_FDCWD, src_name, AT_FDCWD, dst_name, flags) == 0)
         {
           if (x->verbose)
             {
@@ -2351,6 +2357,15 @@ copy_internal (char const *src_name, char const *dst_name,
           return true;
         }
 
+      if ((flags & RENAME_NOREPLACE) && (errno == EEXIST))
+        {
+          /* Pretend the rename succeeded, so the caller (mv)
+             doesn't end up removing the source file.  */
+          if (rename_succeeded)
+            *rename_succeeded = true;
+          return true;
+        }
+
       /* FIXME: someday, consider what to do when moving a directory into
          itself but when source and destination are on different devices.  */
 
-- 
2.13.6