我正在模仿Linux源代码中的gpio-hammer示例。我正在使用Raspberry Pi 3B +，希望LED闪烁。

这就是我要做的：

#include <linux/gpio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>

int main(int argc,const char **argv) {
    int fd,ret;
    struct gpiohandle_request req;
    struct gpiohandle_data data;

    char *gpio_dev_name = "/dev/gpiochip0";
    unsigned int gpio_line = 8;

    memset(&data.values,sizeof(data.values));

    // open device
    fd = open(gpio_dev_name,0);
    if (fd == -1) {
    fprintf(stderr,"Failed to open %s,%s\n",gpio_dev_name,strerror(errno));
    }

    // request gpio output
    req.lineoffsets[0] = gpio_line;
    req.flags = GPIOHANDLE_REQUEST_OUTPUT | GPIOHANDLE_REQUEST_actIVE_LOW;
    strcpy(req.consumer_label,"blink");
    req.lines = 1;
    memcpy(req.default_values,&data,sizeof(req.default_values));

    ret = ioctl(fd,GPIO_GET_LINEHANDLE_IOCTL,&req);
    if (ret == -1) {
        fprintf(stderr,"Failed to issue %s (%d),"GPIO_GET_LINEHANDLE_IOCTL",ret,strerror(errno));
    }

    // blink
    while (1) {
        // read data
        ret = ioctl(fd,GPIOHANDLE_GET_LINE_VALUES_IOCTL,&data);
        if (ret == -1) {
            ret = -errno;
            fprintf(stderr,"GPIOHANDLE_GET_LINE_VALUES_IOCTL",strerror(errno));
            exit(ret);
        }

        // flip digits
        data.values[0] = !data.values[0];

        // set data
        ret = ioctl(fd,GPIOHANDLE_SET_LINE_VALUES_IOCTL,"GPIOHANDLE_SET_LINE_VALUES_IOCTL",strerror(errno));
            exit(ret);
        }

        // delay
        sleep(1);
    }
}

我可以在RPi上编译gpio-hammer示例，并使用./gpio-hammer -n gpiochip0 -o 8运行它。连接到gpiochip0 line8的LED指示灯闪烁。

但是我的程序不起作用。失败

Failed to issue GPIOHANDLE_GET_LINE_VALUES_IOCTL (-22),Invalid argument

我研究了gpiolib的实现。如果ioctl cmd不是ioctl也不是EINVAL (22)，则gpio线句柄的GPIOHANDLE_GET_LINE_VALUES_IOCTL返回GPIOHANDLE_SET_LINE_VALUES_IOCTL。但是事实并非如此。怎么了？