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>

6 files changed, 84 insertions, 6 deletions

diff --git a/src/internal/syscall/unix/copy_file_range_linux.go b/src/internal/syscall/unix/copy_file_range_unix.go
index cf0a279a7a..16a434219e 100644
--- a/src/internal/syscall/unix/copy_file_range_linux.go
+++ b/src/internal/syscall/unix/copy_file_range_unix.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build freebsd || linux
+
 package unix
 
 import (
diff --git a/src/internal/syscall/unix/kernel_version_freebsd.go b/src/internal/syscall/unix/kernel_version_freebsd.go
new file mode 100644
index 0000000000..ef9ee136f3
--- /dev/null
+++ b/src/internal/syscall/unix/kernel_version_freebsd.go
@@ -0,0 +1,48 @@
+// 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 unix
+
+import (
+	"sync"
+	"syscall"
+)
+
+// KernelVersion returns major and minor kernel version numbers
+// parsed from the syscall.Sysctl("kern.osrelease")'s value,
+// or (0, 0) if the version can't be obtained or parsed.
+func KernelVersion() (major, minor int) {
+	release, err := syscall.Sysctl("kern.osrelease")
+	if err != nil {
+		return 0, 0
+	}
+
+	parseNext := func() (n int) {
+		for i, c := range release {
+			if c == '.' {
+				release = release[i+1:]
+				return
+			}
+			if '0' <= c && c <= '9' {
+				n = n*10 + int(c-'0')
+			}
+		}
+		release = ""
+		return
+	}
+
+	major = parseNext()
+	minor = parseNext()
+
+	return
+}
+
+// SupportCopyFileRange reports whether the kernel supports the copy_file_range(2).
+// This function will examine both the kernel version and the availability of the system call.
+var SupportCopyFileRange = sync.OnceValue(func() bool {
+	// The copy_file_range() function first appeared in FreeBSD 13.0.
+	major, _ := KernelVersion()
+	_, err := CopyFileRange(0, nil, 0, nil, 0, 0)
+	return major >= 13 && err != syscall.ENOSYS
+})
diff --git a/src/internal/syscall/unix/kernel_version_freebsd_test.go b/src/internal/syscall/unix/kernel_version_freebsd_test.go
new file mode 100644
index 0000000000..694440e325
--- /dev/null
+++ b/src/internal/syscall/unix/kernel_version_freebsd_test.go
@@ -0,0 +1,23 @@
+// 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 unix_test
+
+import (
+	"internal/syscall/unix"
+	"syscall"
+	"testing"
+)
+
+func TestSupportCopyFileRange(t *testing.T) {
+	major, minor := unix.KernelVersion()
+	t.Logf("Running on FreeBSD %d.%d\n", major, minor)
+
+	_, err := unix.CopyFileRange(0, nil, 0, nil, 0, 0)
+	want := err != syscall.ENOSYS
+	got := unix.SupportCopyFileRange()
+	if want != got {
+		t.Fatalf("SupportCopyFileRange, got %t; want %t", got, want)
+	}
+}
diff --git a/src/internal/syscall/unix/kernel_version_linux.go b/src/internal/syscall/unix/kernel_version_linux.go
index 71e8aa4c57..f3656288ef 100644
--- a/src/internal/syscall/unix/kernel_version_linux.go
+++ b/src/internal/syscall/unix/kernel_version_linux.go
@@ -8,11 +8,9 @@ import (
 	"syscall"
 )
 
-// KernelVersion returns major and minor kernel version numbers, parsed from
-// the syscall.Uname's Release field, or 0, 0 if the version can't be obtained
-// or parsed.
-//
-// Currently only implemented for Linux.
+// KernelVersion returns major and minor kernel version numbers
+// parsed from the syscall.Uname's Release field, or (0, 0) if
+// the version can't be obtained or parsed.
 func KernelVersion() (major, minor int) {
 	var uname syscall.Utsname
 	if err := syscall.Uname(&uname); err != nil {
diff --git a/src/internal/syscall/unix/kernel_version_other.go b/src/internal/syscall/unix/kernel_version_other.go
index fc65c1c823..91c14b31d9 100644
--- a/src/internal/syscall/unix/kernel_version_other.go
+++ b/src/internal/syscall/unix/kernel_version_other.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 unix
 
diff --git a/src/internal/syscall/unix/sysnum_freebsd.go b/src/internal/syscall/unix/sysnum_freebsd.go
new file mode 100644
index 0000000000..2c81110409
--- /dev/null
+++ b/src/internal/syscall/unix/sysnum_freebsd.go
@@ -0,0 +1,7 @@
+// 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 unix
+
+const copyFileRangeTrap uintptr = 569