How go get address of slice as u64? - c

Question

I transfered this C struct:
85 struct spi_ioc_transfer {
86 __u64 tx_buf;
87 __u64 rx_buf;
88
89 __u32 len;
90 __u32 speed_hz;
91
92 __u16 delay_usecs;
93 __u8 bits_per_word;
94 __u8 cs_change;
95 __u32 pad;
96
97 /* If the contents of 'struct spi_ioc_transfer' ever change
98 * incompatibly, then the ioctl number (currently 0) must change;
99 * ioctls with constant size fields get a bit more in the way of
100 * error checking than ones (like this) where that field varies.
101 *
102 * NOTE: struct layout is the same in 64bit and 32bit userspace.
103 */
104 };
to Rust:
struct SpiIocTransfer {
tx_buf: u64,
rx_buf: u64,
len: u32,
speed_hz: u32,
delay_usecs: u16,
bits_per_word: u8,
cs_change: u8,
pad: u32
/* If the contents of 'struct spi_ioc_transfer' ever change
* incompatibly, then the ioctl number (currently 0) must change;
* ioctls with constant size fields get a bit more in the way of
* error checking than ones (like this) where that field varies.
*
* NOTE: struct layout is the same in 64bit and 32bit userspace.
*/
}
However, I'm having problems in filling tx_buf and rx_buf:
C version:
int wiringPiSPIDataRW (int channel, unsigned char *data, int len)
{
struct spi_ioc_transfer spi ;
channel &= 1 ;
memset (&spi, 0, sizeof (spi)) ;
spi.tx_buf = (unsigned long)data ;
spi.rx_buf = (unsigned long)data ;
spi.len = len ;
My Rust version:
pub fn spi_data_rw(&mut self, channel_: i32, data: &[u8], len: u32) -> i32 {
let channel = channel_ & 1;
let spi = SpiIocTransfer::new();
spi.tx_buf = data.as_mut_ptr();//(unsigned long) ?
spi.rx_buf = data.as_mut_ptr();//(unsigned long) ?
Error:
error[E0308]: mismatched types
--> src/w25q.rs:68:29
|
68 | spi.rx_buf = data.as_mut_ptr();//(unsigned long) ?
| ^^^^^^^^^^^^^^^^^ expected `u64`, found *-ptr
|
= note: expected type `u64`
found raw pointer `*mut u8`
How do I get the address of the data slice as an u64?