fs: separate integer conversion for different os

Change-Id: I8ff8e8dc9431b5af52e3ca8e78f0da73cead9008

fs/loopback.go

@@ -123,7 +123,7 @@ var _ = (NodeMknoder)((*LoopbackNode)(nil))
 
 func (n *LoopbackNode) Mknod(ctx context.Context, name string, mode, rdev uint32, out *fuse.EntryOut) (*Inode, syscall.Errno) {
 	p := filepath.Join(n.path(), name)
-	err := syscall.Mknod(p, mode, int(rdev))
+	err := syscall.Mknod(p, mode, intDev(rdev))
 	if err != nil {
 		return nil, ToErrno(err)
 	}

fs/loopback_darwin.go

@@ -123,3 +123,7 @@ func (n *LoopbackNode) CopyFileRange(ctx context.Context, fhIn FileHandle,
 	len uint64, flags uint64) (uint32, syscall.Errno) {
 	return 0, syscall.ENOSYS
 }
+
+func intDev(dev uint32) int {
+	return int(dev)
+}

fs/loopback_linux.go

@@ -61,3 +61,7 @@ func (n *LoopbackNode) CopyFileRange(ctx context.Context, fhIn FileHandle,
 	count, err := unix.CopyFileRange(lfIn.fd, &signedOffIn, lfOut.fd, &signedOffOut, int(len), int(flags))
 	return uint32(count), ToErrno(err)
 }
+
+func intDev(dev uint32) int {
+	return int(dev)
+}