From c0190137ca67014008c92f04926f0cdf22db84b3 Mon Sep 17 00:00:00 2001
From: Giampaolo Rodola <g.rodola@gmail.com>
Date: Mon, 10 May 2021 22:45:06 +0200
Subject: bpo-43743 add comment stating _USE_CP_SENDFILE should not be removed
 (#26024)

---
 Lib/shutil.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Lib/shutil.py b/Lib/shutil.py
index e29fe4d..55cfe35 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -40,6 +40,8 @@ elif _WINDOWS:
     import nt
 
 COPY_BUFSIZE = 1024 * 1024 if _WINDOWS else 64 * 1024
+# This should never be removed, see rationale in:
+# https://bugs.python.org/issue43743#msg393429
 _USE_CP_SENDFILE = hasattr(os, "sendfile") and sys.platform.startswith("linux")
 _HAS_FCOPYFILE = posix and hasattr(posix, "_fcopyfile")  # macOS
 
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