fs: use io.Copy because go supports CopyFileRange

REF: golang/go@7be3f09

Signed-off-by: Wei Fu <fuweid89@gmail.com>

fs/copy.go

@@ -18,8 +18,10 @@ package fs
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
+	"runtime"
 	"sync"
 
 	"github.com/sirupsen/logrus"
@@ -199,5 +201,18 @@ func openAndCopyFile(target, source string) error {
 	}
 	defer tgt.Close()
 
-	return copyFileContent(tgt, src)
+	var tgtWriter io.Writer = tgt
+	if runtime.GOOS != "linux" {
+		tgtWriter = onlyWriter{tgt}
+	}
+
+	buf := bufferPool.Get().(*[]byte)
+	_, err = io.CopyBuffer(tgtWriter, src, *buf)
+	bufferPool.Put(buf)
+
+	return err
+}
+
+type onlyWriter struct {
+	io.Writer
 }

fs/copy_linux.go

@@ -18,7 +18,6 @@ package fs
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"syscall"
 
@@ -62,51 +61,6 @@ func copyFileInfo(fi os.FileInfo, src, name string) error {
 	return nil
 }
 
-const maxSSizeT = int64(^uint(0) >> 1)
-
-func copyFileContent(dst, src *os.File) error {
-	st, err := src.Stat()
-	if err != nil {
-		return fmt.Errorf("unable to stat source: %w", err)
-	}
-
-	size := st.Size()
-	first := true
-	srcFd := int(src.Fd())
-	dstFd := int(dst.Fd())
-
-	for size > 0 {
-		// Ensure that we are never trying to copy more than SSIZE_MAX at a
-		// time and at the same time avoids overflows when the file is larger
-		// than 4GB on 32-bit systems.
-		var copySize int
-		if size > maxSSizeT {
-			copySize = int(maxSSizeT)
-		} else {
-			copySize = int(size)
-		}
-		n, err := unix.CopyFileRange(srcFd, nil, dstFd, nil, copySize, 0)
-		if err != nil {
-			if (err != unix.ENOSYS && err != unix.EXDEV) || !first {
-				return fmt.Errorf("copy file range failed: %w", err)
-			}
-
-			buf := bufferPool.Get().(*[]byte)
-			_, err = io.CopyBuffer(dst, src, *buf)
-			bufferPool.Put(buf)
-			if err != nil {
-				return fmt.Errorf("userspace copy failed: %w", err)
-			}
-			return nil
-		}
-
-		first = false
-		size -= int64(n)
-	}
-
-	return nil
-}
-
 func copyXAttrs(dst, src string, excludes map[string]struct{}, errorHandler XAttrErrorHandler) error {
 	xattrKeys, err := sysx.LListxattr(src)
 	if err != nil {

fs/copy_unix.go

@@ -21,7 +21,6 @@ package fs
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"runtime"
 	"syscall"
@@ -61,14 +60,6 @@ func copyFileInfo(fi os.FileInfo, src, name string) error {
 	return nil
 }
 
-func copyFileContent(dst, src *os.File) error {
-	buf := bufferPool.Get().(*[]byte)
-	_, err := io.CopyBuffer(dst, src, *buf)
-	bufferPool.Put(buf)
-
-	return err
-}
-
 func copyXAttrs(dst, src string, excludes map[string]struct{}, errorHandler XAttrErrorHandler) error {
 	xattrKeys, err := sysx.LListxattr(src)
 	if err != nil {

fs/copy_windows.go

@@ -19,7 +19,6 @@ package fs
 import (
 	"errors"
 	"fmt"
-	"io"
 	"os"
 
 	winio "github.com/Microsoft/go-winio"
@@ -72,13 +71,6 @@ func copyFileInfo(fi os.FileInfo, src, name string) error {
 	return nil
 }
 
-func copyFileContent(dst, src *os.File) error {
-	buf := bufferPool.Get().(*[]byte)
-	_, err := io.CopyBuffer(dst, src, *buf)
-	bufferPool.Put(buf)
-	return err
-}
-
 func copyXAttrs(dst, src string, excludes map[string]struct{}, errorHandler XAttrErrorHandler) error {
 	return nil
 }