From: Andy Pan <panjf2000@gmail.com>
Date: Mon, 27 Feb 2023 04:47:39 +0000 (+0800)
Subject: os: skip zero-copy attempts with copy_file_range(2)/splice(2) for target files with... 
X-Git-Tag: go1.21rc1~1446
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=08a68b73a4843dfe8c4896cace3242b895342511;p=gostls13.git

os: skip zero-copy attempts with copy_file_range(2)/splice(2) for target files with O_APPEND flag

Change-Id: I6cccac9295ab4a9bf7f7a33382a34f31b1c4a000
Reviewed-on: https://go-review.googlesource.com/c/go/+/471496
Auto-Submit: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Andy Pan <panjf2000@gmail.com>
---

diff --git a/src/os/readfrom_linux.go b/src/os/readfrom_linux.go
index 2a81b7abfe..514d873ece 100644
--- a/src/os/readfrom_linux.go
+++ b/src/os/readfrom_linux.go
@@ -16,6 +16,15 @@ var (
 )
 
 func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
+	// Neither copy_file_range(2) nor splice(2) supports destinations opened with
+	// O_APPEND, so don't bother to try zero-copy with these system calls.
+	//
+	// Visit https://man7.org/linux/man-pages/man2/copy_file_range.2.html#ERRORS and
+	// https://man7.org/linux/man-pages/man2/splice.2.html#ERRORS for details.
+	if f.appendMode {
+		return 0, false, nil
+	}
+
 	written, handled, err = f.copyFileRange(r)
 	if handled {
 		return
@@ -74,12 +83,6 @@ func getPollFD(r io.Reader) *poll.FD {
 }
 
 func (f *File) copyFileRange(r io.Reader) (written int64, handled bool, err error) {
-	// copy_file_range(2) does not support destinations opened with
-	// O_APPEND, so don't even try.
-	if f.appendMode {
-		return 0, false, nil
-	}
-
 	var (
 		remain int64
 		lr     *io.LimitedReader