Android系统--输入系统（二）必备Linux知识_实现inotify_epoll.c
课后作业
1. 编写 inotify_epoll.c, 用它来监测tmp/目录: 有文件被创建/删除, 有文件可读出数据
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a. 当在tmp/下创建文件时, 会立刻监测到，并且使用epoll监测该文件
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b. 当文件有数据时，读出数据
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c. 当tmp/下文件被删除时，会立刻监测到，并且把它从epoll中移除不再监测
2. 程序基本框架
（1）初始化--初始化epoll和inotify，获取其fd
（2）添加事件
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对文件夹中文件的创建和删除进行检测--inotify_add_watch(mINotifyFd, dir, IN_DELETE | IN_CREATE);
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将监听事件加入epoll池中，监听事件行为--add_to_epoll(mINotifyFd, mEpollFd);
（3）等待事件发生
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添加、删除文件事件--read_process_inotify_fd(int mINotifyFd, int mEpollFd)
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往文件写入数据--read(mPendingEventItems[i].data.fd, buf, DATA_MAX_LEN);
实现代码：
#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 512
#define MAX_FILES 1024
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
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);
}
/*函数说明：传入文件名，根据epoll_file数组指针，判断每一项指向的是否有内容，如有则比较文件名是否相同*/
int get_epoll_fd_for_name(char *name)
{
int i;
char name_to_find[512];
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;
}
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));
if(res < (int)sizeof(*event)) {
if(errno == EINTR)
return 0;
printf("could not get event, %s
", 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"
", event->wd, event->mask, event->len ? event->name : "");
if(event->len) {
if(event->mask & IN_CREATE) {
printf("create file: %s
", event->name);
char *name = malloc(512);
sprintf(name, "%s/%s", base_dir, event->name);
int tmpFd = open(name, O_RDWR); //如有创建文件，则打开
printf("add to epoll: %s
", name);
add_to_epoll(tmpFd, mEpollFd); //将读取写入文件的事件加入epoll中
epoll_files[tmpFd] = name; //暂时保存文件名称，用于后面释放epoll中的该事件
} else {
printf("delete file: %s
", event->name);
int tmpFd = get_epoll_fd_for_name(event->name); //利用文件名查找对应的事件fd
if (tmpFd >= 0)
{
printf("remove from epoll: %s/%s
", base_dir, event->name);
rm_from_epoll(tmpFd, mEpollFd);
free(epoll_files[tmpFd]);
}
}
}
event_size = sizeof(*event) + event->len;
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>
",argv[0]);
return -1;
}
base_dir = argv[1];
//1. init
/* 1.1 epoll_create */
mEpollFd = epoll_create(8);
/* 1.2 inotify_init */
mINotifyFd = inotify_init();
//2. add
/* 2.1 add watch */
result = inotify_add_watch(mINotifyFd, base_dir, IN_DELETE | IN_CREATE);
/* 2.2 addto epoll*/
add_to_epoll(mINotifyFd, mEpollFd);
/* 3. epoll_wait */
while (1)
{
int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, -1);
for (i = 0; i < pollResult; i++)
{
if (mPendingEventItems[i].data.fd == mINotifyFd) //事件fd为文件添加和删除，则跳转到inotify处理函数
{
read_process_inotify_fd(mINotifyFd, mEpollFd);
}
else
{
printf("Reason: 0x%x
", mPendingEventItems[i].events);
int len = read(mPendingEventItems[i].data.fd, buf, DATA_MAX_LEN);
buf[len] = ' ';
printf("get data: %s
", buf);
}
}
}
return 0;
}
具体操作：
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gcc -o inotify_epoll inotify_epoll.c
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mkdir tmp
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./inotify_epoll tmp/ &
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mkfifo tmp/1 tmp/2 tmp/3
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echo aaa > tmp/1
echo bbb > tmp/2
echo ccc > tmp/3 -
rm tmp/3