[Qemu-devel] What "opaque" stand for?

[Kaiyuan]

Hello, all

I am reviewing source of Qemu. I can see parameter called "opaque" from a lot 
of function like this:
//@hw/timer/xilinx_timer.c
static uint64_t timer_read(void *opaque, hwaddr addr, unsigned int size)

{
...
}


, and its meaning confuse me. What does "opaque" stand for?


Thanks,
Kaiyuan Liang