fs/linux: Clone(): add implementation using ioctl(FICLONE)

internal/fs/file_linux.go

@@ -0,0 +1,45 @@
+//go:build linux
+// +build linux
+
+package fs
+
+import (
+	"golang.org/x/sys/unix"
+	"os"
+)
+
+func init() {
+	registerCloneMethod(doCloneIoctl)
+}
+
+func withFileDescriptors(file1, file2 *os.File, fn func(fd1, fd2 int) (int, error)) (int, error) {
+	conn1, err := file1.SyscallConn()
+	if err != nil {
+		return 0, err
+	}
+	conn2, err := file2.SyscallConn()
+	if err != nil {
+		return 0, err
+	}
+	var n int
+	var err1, err2, err3 error
+	err1 = conn1.Control(func(first uintptr) {
+		err2 = conn2.Control(func(second uintptr) {
+			n, err3 = fn(int(first), int(second))
+		})
+	})
+	if err1 != nil {
+		return n, err1
+	}
+	if err2 != nil {
+		return n, err2
+	}
+	return n, err3
+}
+
+func doCloneIoctl(src, dest *os.File) (cloned bool, err error) {
+	_, err = withFileDescriptors(src, dest, func(srcFd, destFd int) (int, error) {
+		return 0, unix.IoctlFileClone(destFd, srcFd)
+	})
+	return true, err
+}