internal,os: employ copy_file_range(2) for file-to-file copying on FreeBSD

FreeBSD 13.0 introduced the Linux-compatible copy_file_range(2) system call,
we should make use of it.

Ref:
https://www.gnu.org/software/gnulib/manual/html_node/copy_005ffile_005frange.html
https://reviews.freebsd.org/D20584?id=60021
https://man.freebsd.org/cgi/man.cgi?copy_file_range(2)

Change-Id: I75edb5629717289c8887be436613d3a8b3820bdc
Reviewed-on: https://go-review.googlesource.com/c/go/+/604655
Run-TryBot: Andy Pan <panjf2000@gmail.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

5 files changed, 125 insertions, 2 deletions

diff --git a/src/os/export_freebsd_test.go b/src/os/export_freebsd_test.go
new file mode 100644
index 0000000000..56bfcc6c71
--- /dev/null
+++ b/src/os/export_freebsd_test.go
@@ -0,0 +1,9 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+var (
+	PollCopyFileRangeP = &pollCopyFileRange
+)
diff --git a/src/os/readfrom_freebsd_test.go b/src/os/readfrom_freebsd_test.go
new file mode 100644
index 0000000000..186049951f
--- /dev/null
+++ b/src/os/readfrom_freebsd_test.go
@@ -0,0 +1,57 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	"internal/poll"
+	. "os"
+	"testing"
+)
+
+var (
+	copyFileTests = []copyFileTestFunc{newCopyFileRangeTest}
+	copyFileHooks = []copyFileTestHook{hookCopyFileRange}
+)
+
+func testCopyFiles(t *testing.T, size, limit int64) {
+	testCopyFileRange(t, size, limit)
+}
+
+func testCopyFileRange(t *testing.T, size int64, limit int64) {
+	dst, src, data, hook, name := newCopyFileRangeTest(t, size)
+	testCopyFile(t, dst, src, data, hook, limit, name)
+}
+
+// newCopyFileRangeTest initializes a new test for copy_file_range.
+// It hooks package os' call to poll.CopyFileRange and returns the hook,
+// so it can be inspected.
+func newCopyFileRangeTest(t *testing.T, size int64) (dst, src *File, data []byte, hook *copyFileHook, name string) {
+	t.Helper()
+
+	name = "newCopyFileRangeTest"
+
+	dst, src, data = newCopyFileTest(t, size)
+	hook, _ = hookCopyFileRange(t)
+
+	return
+}
+
+func hookCopyFileRange(t *testing.T) (hook *copyFileHook, name string) {
+	name = "hookCopyFileRange"
+
+	hook = new(copyFileHook)
+	orig := *PollCopyFileRangeP
+	t.Cleanup(func() {
+		*PollCopyFileRangeP = orig
+	})
+	*PollCopyFileRangeP = func(dst, src *poll.FD, remain int64) (int64, bool, error) {
+		hook.called = true
+		hook.dstfd = dst.Sysfd
+		hook.srcfd = src.Sysfd
+		hook.written, hook.handled, hook.err = orig(dst, src, remain)
+		return hook.written, hook.handled, hook.err
+	}
+	return
+}
diff --git a/src/os/readfrom_unix_test.go b/src/os/readfrom_unix_test.go
index 9ed633639a..98a4e6af81 100644
--- a/src/os/readfrom_unix_test.go
+++ b/src/os/readfrom_unix_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build linux || solaris
+//go:build freebsd || linux || solaris
 
 package os_test
 
diff --git a/src/os/zero_copy_freebsd.go b/src/os/zero_copy_freebsd.go
new file mode 100644
index 0000000000..4751ca46be
--- /dev/null
+++ b/src/os/zero_copy_freebsd.go
@@ -0,0 +1,57 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"internal/poll"
+	"io"
+)
+
+var pollCopyFileRange = poll.CopyFileRange
+
+func (f *File) writeTo(w io.Writer) (written int64, handled bool, err error) {
+	return 0, false, nil
+}
+
+func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
+	// copy_file_range(2) doesn't supports destinations opened with
+	// O_APPEND, so don't bother to try zero-copy with these system calls.
+	//
+	// Visit https://man.freebsd.org/cgi/man.cgi?copy_file_range(2)#ERRORS for details.
+	if f.appendMode {
+		return 0, false, nil
+	}
+
+	var (
+		remain int64
+		lr     *io.LimitedReader
+	)
+	if lr, r, remain = tryLimitedReader(r); remain <= 0 {
+		return 0, true, nil
+	}
+
+	var src *File
+	switch v := r.(type) {
+	case *File:
+		src = v
+	case fileWithoutWriteTo:
+		src = v.File
+	default:
+		return 0, false, nil
+	}
+
+	if src.checkValid("ReadFrom") != nil {
+		// Avoid returning the error as we report handled as false,
+		// leave further error handling as the responsibility of the caller.
+		return 0, false, nil
+	}
+
+	written, handled, err = pollCopyFileRange(&f.pfd, &src.pfd, remain)
+	if lr != nil {
+		lr.N -= written
+	}
+
+	return written, handled, wrapSyscallError("copy_file_range", err)
+}
diff --git a/src/os/zero_copy_stub.go b/src/os/zero_copy_stub.go
index fb70124fca..0470a205ef 100644
--- a/src/os/zero_copy_stub.go
+++ b/src/os/zero_copy_stub.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !linux && !solaris
+//go:build !freebsd && !linux && !solaris
 
 package os