输入系统：epoll & inotify

一、epoll

作用：检测一个或多个文件的可读、可写等属性变化：

代码示例：

#include <sys/epoll.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>


#if 0
typedef union epoll_data {
   void        *ptr;
   int          fd;
   uint32_t     u32;
   uint64_t     u64;
} epoll_data_t;

#endif


#define DATA_MAX_LEN 500

/* usage: epoll <file1> [file2] [file3] ... */

int add_to_epoll(int fd, int epollFd)
{
    int result;
    struct epoll_event eventItem;
    memset(&eventItem, 0, sizeof(eventItem));
    eventItem.events = EPOLLIN;
    eventItem.data.fd = fd;
    result = epoll_ctl(epollFd, EPOLL_CTL_ADD, fd, &eventItem);
    return result;
}

void rm_from_epoll(int fd, int epollFd)
{
    epoll_ctl(epollFd, EPOLL_CTL_DEL, fd, NULL);
}


int main(int argc, char **argv)
{
    int mEpollFd;
    int i;
    char buf[DATA_MAX_LEN];

    // Maximum number of signalled FDs to handle at a time.
    static const int EPOLL_MAX_EVENTS = 16;

    // The array of pending epoll events and the index of the next event to be handled.
    struct epoll_event mPendingEventItems[EPOLL_MAX_EVENTS];

    
    if (argc < 2)
    {
        printf("Usage: %s <file1> [file2] [file3] ...\n", argv[0]);
        return -1;
    }

    /* epoll_create */
    mEpollFd = epoll_create(8);

    /* for each file:
     * open it
     * add it to epoll: epoll_ctl(...EPOLL_CTL_ADD...)
     */
    for (i = 1; i < argc; i++)     
    {
        //int tmpFd = open(argv[i], O_RDONLY|O_NONBLOCK);
        int tmpFd = open(argv[i], O_RDWR);
        add_to_epoll(tmpFd, mEpollFd);
    }

    /* epoll_wait */
    while (1)
    {
        
        int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, -1);
        for (i = 0; i < pollResult; i++)
        {
            printf("Reason: 0x%x\n", mPendingEventItems[i].events);
            int len = read(mPendingEventItems[i].data.fd, buf, DATA_MAX_LEN);
            buf[len] = '\0';
            printf("get data: %s\n", buf);
            //sleep(3);
        }
        
    }
    
    return 0;
}

 

二、inotify

作用： 监控一个目录下文件的增加、删除事件:

代码示例：

#include <unistd.h>
#include <stdio.h>
#include <sys/inotify.h>
#include <string.h>
#include <errno.h>


/*
 *参考: frameworks\native\services\inputflinger\EventHub.cpp
 */

/*Usage: inotify <dir> */

int read_process_inotify_fd(int fd)
{
    int res;
    char event_buf[512];
    int event_size;
    int event_pos = 0;
    struct inotify_event *event;
    
    /* read */    
    res = read(fd, event_buf, sizeof(event_buf));

    if(res < (int)sizeof(*event)) {
        if(errno == EINTR)
            return 0;
        printf("could not get event, %s\n", strerror(errno));
        return -1;
    }

    /* process
     * 读到的数据是1个或多个inotify_event
     * 它们的长度不一样
     * 逐个处理
     */

    while(res >= (int)sizeof(*event)) {
        event = (struct inotify_event *)(event_buf + event_pos);
        //printf("%d: %08x \"%s\"\n", event->wd, event->mask, event->len ? event->name : "");
        if(event->len) {
            if(event->mask & IN_CREATE) {
                printf("create file: %s\n", event->name);
            } else {
                printf("delete file: %s\n", event->name);
            }
        }
        event_size = sizeof(*event) + event->len;
        res -= event_size;
        event_pos += event_size;
    }
    return 0;
}

int main(int argc, char **argv)
{
    int mINotifyFd;
    int result;

    if (argc != 2)
    {
        printf("Usage: %s <dir>\n", argv[0]);
        return -1;
    }

    /* inotify_init */

    mINotifyFd = inotify_init();

    /* add watch */
    result = inotify_add_watch(mINotifyFd, argv[1], IN_DELETE | IN_CREATE);

    /* read */
    while (1)
    {
        read_process_inotify_fd(mINotifyFd);
    }

    return 0;
}

 

三、inotify和epoll的综合应用：

代码示例：

#include <sys/epoll.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/inotify.h>
#include <stdlib.h>
#include <errno.h>


#define DATA_MAX_LEN 500
#define MAX_FILES 1000

static char *base_dir;
static char *epoll_files[MAX_FILES];

#if 0
typedef union epoll_data {
   void        *ptr;
   int          fd;
   uint32_t     u32;
   uint64_t     u64;
} epoll_data_t;

#endif



/* usage: epoll <file1> [file2] [file3] ... */

int add_to_epoll(int fd, int epollFd)
{
    int result;
    struct epoll_event eventItem;
    memset(&eventItem, 0, sizeof(eventItem));
    eventItem.events = EPOLLIN;
    eventItem.data.fd = fd;
    result = epoll_ctl(epollFd, EPOLL_CTL_ADD, fd, &eventItem);  //添加一个文件句柄到epoll监测列表
    return result;
}

void rm_from_epoll(int fd, int epollFd)
{
    epoll_ctl(epollFd, EPOLL_CTL_DEL, fd, NULL);
}

//通过文件名找到epoll监测列表中对应该文件的下标
int get_epoll_fd_for_name(char *name)
{
    int i;
    char name_to_find[500];
    sprintf(name_to_find, "%s/%s", base_dir, name);

    for (i = 0; i < MAX_FILES; i++)
    {
        if (!epoll_files[i])
            continue;
        
        if (!strcmp(epoll_files[i], name_to_find))
            return i;
    }
    return -1;
}


/*
 *参考: frameworks\native\services\inputflinger\EventHub.cpp
 */

/*Usage: inotify <dir> */

int read_process_inotify_fd(int mINotifyFd, int mEpollFd)
{
    int res;
    char event_buf[512];
    int event_size;
    int event_pos = 0;
    struct inotify_event *event;
    
    /* read */    
    res = read(mINotifyFd, event_buf, sizeof(event_buf)); //返回值是一个或多个inotify_event总和大小

    if(res < (int)sizeof(*event)) {
        if(errno == EINTR)
            return 0;
        printf("could not get event, %s\n", strerror(errno));
        return -1;
    }

    /* process
     * 读到的数据是1个或多个inotify_event
     * 它们的长度不一样
     * 逐个处理
     */

    while(res >= (int)sizeof(*event)) {
        event = (struct inotify_event *)(event_buf + event_pos);
        //printf("%d: %08x \"%s\"\n", event->wd, event->mask, event->len ? event->name : "");
        if(event->len) {
            if(event->mask & IN_CREATE) {
                printf("create file: %s\n", event->name);
                char *name = malloc(512);
                sprintf(name, "%s/%s", base_dir, event->name);
                int tmpFd = open(name, O_RDWR);

                printf("add to epoll: %s\n", name);
                add_to_epoll(tmpFd, mEpollFd);

                epoll_files[tmpFd] = name;
                    
            } else {
                printf("delete file: %s\n", event->name);
                int tmpFd = get_epoll_fd_for_name(event->name);
                if (tmpFd >= 0)
                {
                    printf("remove from epoll: %s/%s\n", base_dir, event->name);
                    rm_from_epoll(tmpFd, mEpollFd);
                    free(epoll_files[tmpFd]);
                }
            }
        }
        event_size = sizeof(*event) + event->len; //一个event大小=结构体大小+所含数据长度
        res -= event_size;
        event_pos += event_size;
    }
    return 0;
}


int main(int argc, char **argv)
{
    int mEpollFd;
    int i;
    char buf[DATA_MAX_LEN];
    int mINotifyFd;
    int result;

    // Maximum number of signalled FDs to handle at a time.
    static const int EPOLL_MAX_EVENTS = 16;

    // The array of pending epoll events and the index of the next event to be handled.
    struct epoll_event mPendingEventItems[EPOLL_MAX_EVENTS];

    
    if (argc != 2)
    {
        printf("Usage: %s <tmp>\n", argv[0]);
        return -1;
    }

    base_dir = argv[1];

    /* epoll_create */
    mEpollFd = epoll_create(8); //创建epoll文件句柄

    /* inotify_init */
    mINotifyFd = inotify_init(); //创建inotify文件句柄，可用epoll监测

    /* add watch */
    result = inotify_add_watch(mINotifyFd, base_dir, IN_DELETE | IN_CREATE); //设置监测inotify文件句柄

    add_to_epoll(mINotifyFd, mEpollFd); //使用epoll监测inotify文件句柄


    /* epoll_wait */
    while (1)
    {  
        int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, -1); //当文件有数据可读时返回
        for (i = 0; i < pollResult; i++)
        {
            if (mPendingEventItems[i].data.fd == mINotifyFd) //当监测到的文件句柄为mINodifyFd（目录）时说明有文件创建/删除
            {
                read_process_inotify_fd(mINotifyFd, mEpollFd); //根据event->name 添加/移除 对该文件的监测
            }
            else
            {
                printf("Reason: 0x%x\n", mPendingEventItems[i].events);
                int len = read(mPendingEventItems[i].data.fd, buf, DATA_MAX_LEN);
                buf[len] = '\0';
                printf("get data: %s\n", buf);
                //sleep(3);
            }
        }
        
    }
    
    return 0;
}