fn fileSeekBy(userdata: ?*anyopaque, file: File, offset: i64) File.SeekError!void
fn fileSeekBy(userdata: ?*anyopaque, file: File, offset: i64) File.SeekError!void { const ev: *Evented = @ptrCast(@alignCast(userdata)); return ev.lseek(file.handle, @bitCast(offset), c.SEEK.CUR); }