linux文件系统变化通知机制(inotify)

如果我们需要实时的了解一个文件夹或者目录的变化，我们可以使用linux文件系统变化通知机制(inotify)，只要有变化，都会收到通知。

inotify是用来监视文件系统事件的机制，在linux 2.6.13内核中引入。

该机制可以用来监视文件和目录，当文件或目录发生变化时，内核会将文件或目录的变化发送给inotify文件描述符，在应用层只需调用read()就可以读取这些事件，非常的方便。更好的是，inotify文件描述符还可以使用select、poll、epoll这些接口来监听，当有事件发生是，inotify文件描述符会可读

1、api介绍

#include <sys/inotify.h>/* Create and initialize inotify instance.  */int inotify_init (void);(1) inotify_init()在内核中创建一个实体，并返回一个文件描述符fd。(2) 成功的话返回文件描述符，失败返回-1。/* Add watch of object NAME to inotify instance FD.  Notify about events specified by MASK.  */int inotify_add_watch (int __fd, const char *__name, uint32_t __mask);创建监视器要提供：(1) inotify实例inotify_init返回的文件描述符：fd。(2) 监视目标路径：name。(3) 监视事件列表：mask。(4) 如果成功，返回监视器描述符wd，否则返回-1。/* Remove the watch specified by WD from the inotify instance FD.  */int inotify_rm_watch (int __fd, int __wd);用于从监视器列表中删除一个监视器。(1) fd为inotify_init返回的文件描述符。(2) wd为inotify_add_watch返回监视器描述符。(3) 返回值：0 成功，-1 失败。

2、事件结构体

/* Structure describing an inotify event.  */struct inotify_event{  int wd;       /* Watch descriptor.  */  uint32_t mask;    /* Watch mask.  */  uint32_t cookie;  /* Cookie to synchronize two events.  */  uint32_t len;     /* Length (including NULs) of name.  */  char name;    /* Name.  */};（1）wd为监视器描述符。（2）mask代表当前事件是什么事件，在事件列表可查。（3）len为name的长度。动态变化的，其实就是被监视发生变化的文件夹名或者文件名。（3）、被监视到的文件夹名称/文件名。

3、事件列表

/* Supported events suitable for MASK parameter of INOTIFY_ADD_WATCH.  */#define IN_ACCESS    0x00000001 /* File was accessed.  */#define IN_MODIFY    0x00000002 /* File was modified.  */#define IN_ATTRIB    0x00000004 /* Metadata changed.  */#define IN_CLOSE_WRITE   0x00000008 /* Writtable file was closed.  */#define IN_CLOSE_NOWRITE 0x00000010 /* Unwrittable file closed.  */#define IN_CLOSE     (IN_CLOSE_WRITE | IN_CLOSE_NOWRITE) /* Close.  */#define IN_OPEN      0x00000020 /* File was opened.  */#define IN_MOVED_FROM    0x00000040 /* File was moved from X.  */#define IN_MOVED_TO      0x00000080 /* File was moved to Y.  */#define IN_MOVE      (IN_MOVED_FROM | IN_MOVED_TO) /* Moves.  */#define IN_CREATE    0x00000100 /* Subfile was created.  */#define IN_DELETE    0x00000200 /* Subfile was deleted.  */#define IN_DELETE_SELF   0x00000400 /* Self was deleted.  */#define IN_MOVE_SELF     0x00000800 /* Self was moved.  *//* Events sent by the kernel.  */#define IN_UNMOUNT   0x00002000 /* Backing fs was unmounted.  */#define IN_Q_OVERFLOW    0x00004000 /* Event queued overflowed.  */#define IN_IGNORED   0x00008000 /* File was ignored.  *//* Helper events.  */#define IN_CLOSE     (IN_CLOSE_WRITE | IN_CLOSE_NOWRITE)    /* Close.  */#define IN_MOVE      (IN_MOVED_FROM | IN_MOVED_TO)      /* Moves.  *//* Special flags.  */#define IN_ONLYDIR   0x01000000 /* Only watch the path if it is a                       directory.  */#define IN_DONT_FOLLOW   0x02000000 /* Do not follow a sym link.  */#define IN_MASK_ADD  0x20000000 /* Add to the mask of an already                       existing watch.  */#define IN_ISDIR     0x40000000 /* Event occurred against dir.  */#define IN_ONESHOT   0x80000000 /* Only send event once.  *//* All events which a program can wait on.  */#define IN_ALL_EVENTS    (IN_ACCESS | IN_MODIFY | IN_ATTRIB | IN_CLOSE_WRITE  \              | IN_CLOSE_NOWRITE | IN_OPEN | IN_MOVED_FROM        \              | IN_MOVED_TO | IN_CREATE | IN_DELETE           \              | IN_DELETE_SELF | IN_MOVE_SELF)

4、测试程序

////  test_inotify.cpp//  ////  Created by jianjian Qi on 9/11/16.//  Copyright © 2016 tgbtgb. All rights reserved.//#include <stdio.h>#include <string.h>#include <stdlib.h>#include <sys/inotify.h>#include <unistd.h>#define EVENT_NUM 12#define BUFF_SIZE 1024char *event_str[EVENT_NUM] ={  "IN_ACCESS",  "IN_MODIFY",  "IN_ATTRIB",  "IN_CLOSE_WRITE",  "IN_CLOSE_NOWRITE",  "IN_OPEN",  "IN_MOVED_FROM",  "IN_MOVED_TO",  "IN_CREATE",  "IN_DELETE",  "IN_DELETE_SELF",  "IN_MOVE_SELF"};int main(int argc, char *argv[]){  int fd;  int wd;  int len;  int nread;  char buf[BUFF_SIZE];  struct inotify_event *event;  int i;  if (argc < 2)  {    fprintf(stderr, "%s path\n", argv[0]);    return -1;  }  fd = inotify_init();  if ( fd < 0 )  {    fprintf(stderr, "inotify_init failed\n");    return -1;  }  wd = inotify_add_watch(fd, argv[1], IN_ALL_EVENTS);  if (wd < 0)  {    fprintf(stderr, "inotify_add_watch %s failed\n", argv[1]);    return -1;  }  memset(buf, 0, BUFF_SIZE);  while ( (len = read(fd, buf, sizeof(buf) - 1)) > 0 )  {    nread = 0;    while ( len > 0 )    {      event = (struct inotify_event *)&buf[nread];      for ( i=0; i<EVENT_NUM; i++)      {        if ((event->mask >> i) & 1)        {          if (event->len > 0)          {            fprintf(stdout, "%s --- %s\n", event->name, event_str[i]);          }          else          {            fprintf(stdout, "%s --- %s\n", " ", event_str[i]);          }        }      }      nread = nread + sizeof(struct inotify_event) + event->len;      len   = len - sizeof(struct inotify_event) - event->len;    }  }  return 0;}

5、编译

#g++ test_inotify.cpp

6、运行

#./a.out ~/Desktop/test/
index0.ts — IN_CREATE
index0.ts — IN_OPEN
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_MODIFY
index0.ts — IN_CLOSE_WRITE
index1.ts — IN_CREATE
index1.ts — IN_OPEN
index.m3u8.tmp — IN_CREATE
index.m3u8.tmp — IN_OPEN
index.m3u8.tmp — IN_MODIFY
index.m3u8.tmp — IN_CLOSE_WRITE
index.m3u8.tmp — IN_MOVED_FROM
index.m3u8 — IN_MOVED_TO

参考网址：http://linux.die.net/man/7/inotify