#include <sys/ioctl.h>
#include <linux/spi/spidev.h>

int fd;
unsigned char buf[8192]; // Nice if this is page aligned
unsigned char cmd[2];
struct spi_ioc_txr xfer[3]; //struct is 32 bytes x3
int status;

fd = open('/dev/spidev<bus>.<device>', O_RDWR)
// handle error if fd < 0

memset - buf, cmd, xfer
cmd[0] = address >> 4;
cmd[1] = (address << 4) & 0xff;
if(read_command) {
    cmd[1] |= 1 << 3;
} // else write command
xfer[0].tx_buf = (unsigned long)cmd;
xfer[0].len = 2
xfer[0].speed_hz = 20000000; // 20,000,000 20MHz

xfer[1].rx_buf = (unsigned long)buf;
xfer[1].len = 4096;
xfer[1].speed_hz = 20000000;
xfer[2].rx_buf = (unsigned long)(buf + 4096);
xfer[2].len = 4096;
xfer[2].speed_hz = 20000000;

status = ioctl(fd, SPI_IOC_MESSAGE(3), xfer);
// error if < 0
// data now in xfer as bytes

$ sudo rmmod spidev
$ sudo modprobe spidev bufsiz=8192

$ echo "options spidev bufsiz=8192" | sudo tee /etc/modprobe.d/spidev.conf