unix: add Darwin support for clonefile syscalls

This commit adds support for three Darwin-specific calls that accelerate
the copying of files:

* clonefile()
* clonefileat()
* fclonefileat()

Fixes golang/go#41366

Change-Id: I7e6c525fc23d8474ea85feff24314d3d672d87ed
Reviewed-on: https://go-review.googlesource.com/c/sys/+/254757
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Tobias Klauser <tobias.klauser@gmail.com>

unix/syscall_darwin_test.go

@@ -4,6 +4,18 @@
 
 package unix_test
 
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"path"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+var testData = []byte("This is a test\n")
+
 // stringsFromByteSlice converts a sequence of attributes to a []string.
 // On Darwin, each entry is a NULL-terminated string.
 func stringsFromByteSlice(buf []byte) []string {
@@ -17,3 +29,152 @@ func stringsFromByteSlice(buf []byte) []string {
 	}
 	return result
 }
+
+func createTestFile(t *testing.T, dir string) (f *os.File, cleanup func() error) {
+	file, err := ioutil.TempFile(dir, "TestClonefile")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = file.Write(testData)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = file.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return file, func() error {
+		return os.Remove(file.Name())
+	}
+}
+
+func TestClonefile(t *testing.T) {
+	file, cleanup := createTestFile(t, "")
+	defer cleanup()
+
+	clonedName := file.Name() + "-cloned"
+	err := unix.Clonefile(file.Name(), clonedName, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(clonedName)
+
+	clonedData, err := ioutil.ReadFile(clonedName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(testData, clonedData) {
+		t.Errorf("Clonefile: got %q, expected %q", clonedData, testData)
+	}
+}
+
+func TestClonefileatWithCwd(t *testing.T) {
+	file, cleanup := createTestFile(t, "")
+	defer cleanup()
+
+	clonedName := file.Name() + "-cloned"
+	err := unix.Clonefileat(unix.AT_FDCWD, file.Name(), unix.AT_FDCWD, clonedName, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.Remove(clonedName)
+
+	clonedData, err := ioutil.ReadFile(clonedName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(testData, clonedData) {
+		t.Errorf("Clonefileat: got %q, expected %q", clonedData, testData)
+	}
+}
+
+func TestClonefileatWithRelativePaths(t *testing.T) {
+	srcDir, err := ioutil.TempDir("", "src")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(srcDir)
+
+	dstDir, err := ioutil.TempDir("", "dest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dstDir)
+
+	srcFd, err := unix.Open(srcDir, unix.O_RDONLY|unix.O_DIRECTORY, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close(srcFd)
+
+	dstFd, err := unix.Open(dstDir, unix.O_RDONLY|unix.O_DIRECTORY, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close(dstFd)
+
+	srcFile, cleanup := createTestFile(t, srcDir)
+	defer cleanup()
+
+	dstFile, err := ioutil.TempFile(dstDir, "TestClonefileat")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.Remove(dstFile.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	src := path.Base(srcFile.Name())
+	dst := path.Base(dstFile.Name())
+	err = unix.Clonefileat(srcFd, src, dstFd, dst, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	clonedData, err := ioutil.ReadFile(dstFile.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(testData, clonedData) {
+		t.Errorf("Clonefileat: got %q, expected %q", clonedData, testData)
+	}
+}
+
+func TestFclonefileat(t *testing.T) {
+	file, cleanup := createTestFile(t, "")
+	defer cleanup()
+
+	fd, err := unix.Open(file.Name(), unix.O_RDONLY, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close(fd)
+
+	dstFile, err := ioutil.TempFile("", "TestFclonefileat")
+	if err != nil {
+		t.Fatal(err)
+	}
+	os.Remove(dstFile.Name())
+
+	err = unix.Fclonefileat(fd, unix.AT_FDCWD, dstFile.Name(), 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	clonedData, err := ioutil.ReadFile(dstFile.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(testData, clonedData) {
+		t.Errorf("Fclonefileat: got %q, expected %q", clonedData, testData)
+	}
+}