韦东山设备信息查询例程学习

1.查询 阻塞机制

#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdio.h>

int main(int argc, char **argv)
{
    
    int fd;
    int ret;
    struct input_id id;
    int len;
    unsigned int evbit[2];
    unsigned char byte;
    int i;
    int bit;
    char read_buff[100] = {
    '\0'};
    struct input_event event;
    char *ev_names[] = {
    
		"EV_SYN ",
		"EV_KEY ",
		"EV_REL ",
		"EV_ABS ",
		"EV_MSC ",
		"EV_SW ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"NULL ",
		"EV_LED ",
		"EV_SND ",
		"NULL ",
		"EV_REP ",
		"EV_FF ",
		"EV_PWR ",
		};
    if (argc != 2)
	{
    
		printf("Usage: %s <dev>\ne.g., %s /dev/input/event0\n", argv[0], argv[0]);
		return -1;
	}

    fd = open(argv[1], O_RDWR ); /*| O_NONBLOCK*/
    if (fd < 0)
    {
    
        return -1;
    }
    ret = ioctl(fd, EVIOCGID, &id);
    if (ret == 0)
    {
    
        printf("bustype = 0x%x\n", id.bustype );
		printf("vendor = 0x%x\n", id.vendor  );
		printf("product = 0x%x\n", id.product );
		printf("version = 0x%x\n", id.version );
    }

    len = ioctl(fd, EVIOCGBIT(0, sizeof(evbit)), &evbit);

    if (len > 0)
    {
    
        printf("support ev type:");
        for (i = 0; i < len; i++)
        {
    
            byte = ((unsigned char *)evbit)[i];
            for (bit = 0; bit < 8; bit++)
            {
    
                if (byte & (1 << bit))
                {
    
                    printf("%s ", ev_names[i * 8 + bit]);
                }
            }
        }
        printf("\n");
    }
    while (1)
    {
    
        len = read(fd, &event, sizeof(event));
		if (len == sizeof(event))
		{
    
			printf("get event: type = 0x%x, code = 0x%x, value = 0x%x\n", event.type, event.code, event.value);
		}
        else
        {
    
            printf("read err.\n");
        }
    }
    return 0;
}

2.poll机制

#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <poll.h>

int main(int argc, char **argv)
{
    
    int fd;
    int ret;
    struct input_event event;
    struct pollfd fds[1];
    nfds_t nfds = 1;
   
    if (argc != 2)
	{
    
		printf("Usage: %s <dev>\ne.g., %s /dev/input/event0\n", argv[0], argv[0]);
		return -1;
	}

    fd = open(argv[1], O_RDWR ); /*| O_NONBLOCK*/
    if (fd < 0)
    {
    
        return -1;
    }
   
    fds[0].fd = fd;
    fds[0].events = POLLIN;
   
    while (1)
    {
    
   		fds[0].revents = 0;
        ret = poll(fds, nfds, 3000);
        if (ret > 0)
        {
    
            if (fds[0].revents == POLLIN)
            {
    
                while (read(fd, &event, sizeof(event)) == sizeof(event))
                {
    
					printf("get event: type = 0x%x, code = 0x%x, value = 0x%x\n", event.type, event.code, event.value);
                }
            }
            else
            {
    
                printf("read error.\n");
            }
        }
        else if(ret == 0)
        {
    
            printf("time out\n");
        }
        else
        {
    
            printf("poll err.\n");
        }
    }
    return 0;
}

3.select机制

#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>

/* According to earlier standards */
#include <sys/time.h>

int main(int argc, char **argv)
{
    
    int fd;
    int ret;
   
    struct input_event event;
    fd_set readfd;
    unsigned int nfds = 1;
    struct timeval time_val;

    if (argc != 2)
	{
    
		printf("Usage: %s <dev>\ne.g., %s /dev/input/event0\n", argv[0], argv[0]);
		return -1;
	}

    fd = open(argv[1], O_RDWR | O_NONBLOCK); 
    if (fd < 0)
    {
    
        return -1;
    }
    
    nfds = fd +1;
    FD_ZERO(&readfd);
    
    while (1)
    {
    
        time_val.tv_sec = 3;
        time_val.tv_usec = 0;
        FD_SET(fd, &readfd);
        ret = select(nfds, &readfd, NULL, NULL, &time_val);
        if (ret > 0)
        {
    
            if (FD_ISSET(fd, &readfd))
            {
    
                while (read(fd, &event, sizeof(event)) == sizeof(event))
                {
    
					printf("get event: type = 0x%x, code = 0x%x, value = 0x%x\n", event.type, event.code, event.value);
                }
            }
            else
            {
    
                printf("read error.\n");
            }
        }
        else if(ret == 0)
        {
    
            printf("time out\n");
        }
        else
        {
    
            printf("select err.\n");
        }
    }
    return 0;
}

poll和select在open的时候，要使用NONBLOCK， 即非阻塞。原因可以查看这里。

4.异步机制

#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>


int fd;
void my_sig_process(int sig)
{
    
    struct input_event event;
    while (read(fd, &event, sizeof(event)) == sizeof(event))
    {
    
        printf("get event: type = 0x%x, code = 0x%x, value = 0x%x\n", event.type, event.code, event.value);	
    }
}
int main(int argc, char **argv)
{
    
    
    int ret = 0;
    int cnt = 0;

    if (argc != 2)
	{
    
		printf("Usage: %s <dev>\ne.g., %s /dev/input/event0\n", argv[0], argv[0]);
		return -1;
	}
    
    fd = open(argv[1], O_RDWR | O_NONBLOCK); 
    if (fd < 0)
    {
    
        return -1;
    }
    
    signal(SIGIO, my_sig_process);
    fcntl(fd, F_SETOWN, getpid());
    ret = fcntl(fd, F_GETFL);
	fcntl(fd, F_SETFL, ret | FASYNC);

    while (1)
    {
    
        printf("main loop count = %d\n", cnt++);
		sleep(1);
    }
    return 0;
}