inotify例程

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最新推荐文章于 2024-07-24 10:10:28 发布

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分类专栏： linux application 文章标签： file events buffer descriptor struct attributes

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#include
#include
#include

char * monitored_files [] = {
 " ./tmp_file " ,
 " ./tmp_dir " ,
 " /mnt/sda3/windows_file "
} ;

struct wd_name {
 int wd ;
 char * name ;
} ;

#define WD_NUM 3
struct wd_name wd_array [ WD_NUM ] ; //用于存储文件路径名和watch描述符

//inotify机制事件对应说明数组
char * event_array [] = {
 " File was accessed " ,
 " File was modified " ,
 " File attributes were changed " ,
 " writtable file closed " ,
 " Unwrittable file closed " ,
 " File was opened " ,
 " File was moved from X " ,
 " File was moved to Y " ,
 " Subfile was created " ,
 " Subfile was deleted " ,
 " Self was deleted " ,
 " Self was moved " ,
 "" ,
 " Backing fs was unmounted " ,
 " Event queued overflowed " ,
 " File was ignored "
} ;
#define EVENT_NUM 16
#define MAX_BUF_SIZE 1024

int main ( void )
{
 int fd ;
 int wd ;
 char buffer [ 1024 ] ;
 char * offset = NULL ;
 struct inotify_event * event ;
 int len , tmp_len ;
 char strbuf [ 16 ] ;
 int i = 0 ;

 fd = inotify_init () ;
 if ( fd < 0 ) {
 printf ( " Fail to initialize inotify. / n " ) ;
 exit ( - 1 ) ;

 }
 for ( i = 0 ; i < WD_NUM ; i ++ ) {
 wd_array . name = monitored_files ; //存入文件路径名
 //给路径wd_array.name添加一个watch，监视所有事件，wd为返回的watch描述符
 wd = inotify_add_watch ( fd , wd_array . name , IN_ALL_EVENTS ) ;
 if ( wd < 0 ) {
 printf ( " Can't add watch for %s. / n " , wd_array . name ) ;
 exit ( - 1 ) ;
 }

 wd_array . wd = wd ;
 }

 while ( len = read ( fd , buffer , MAX_BUF_SIZE )) { //读取多个事件
 offset = buffer ;
 printf ( " Some event happens, len = %d. / n " , len ) ; //打印实际读取的长度
 event = ( struct inotify_event * ) buffer ; //得到事件

 while ((( char * ) event - buffer ) < len ) {
 if ( event -> mask & IN_ISDIR ) { //目录
 memcpy ( strbuf , " Direcotory " , 11 ) ;
 //“Direcotory”字符串长度为11
 }
 else {
 memcpy ( strbuf , " File " , 5 ) ;
 //“File”字符串长度为5，包括后面加一个空格
 }
 printf ( " Object type: %s / n " , strbuf ) ;

 for ( i = 0 ; i < WD_NUM ; i ++ ) {
 if ( event -> wd != wd_array . wd )
 continue ;
 printf ( " Object name: %s / n " , wd_array . name ) ;
 //打印文件路径名
 break ;
 }

 printf ( " Event mask: %08X / n " , event -> mask ) ; //打印事件掩码
 for ( i = 0 ; i < EVENT_NUM ; i ++ ) {
 if ( event_array [ 0 ] == '/ 0 ' )
 //空字符串行，说明事件对应说明不存在
 continue ;
 //将事件掩码的位匹配数组成员，如：00000020，即100000，对应i为5
 if ( event -> mask & ( 1 < ) ; 　
 //打印事件对应的说明字符串
 }
 }

 tmp_len = sizeof ( struct inotify_event ) + event -> len ;
 event = ( struct inotify_event * )( offset + tmp_len ) ; //得到下一个事件
 offset += tmp_len ;
 }
 }
}

C Code Snip

Incomplete, for a better example look at the Beagle source code in glue/inotify-glue.c.

// Initialize Inotify
fd = inotify_init ();
if (fd < 0) return -errno;

// Add a Watch
int wd;
wd = inotify_add_watch (fd, filename, mask);
if (wd < 0) return -errno;

// Read an inotify event (buffer should be at least the size of
static struc inotify_event *buffer = NULL;
buffer_size = sizeof (struct inotify_event);
*nr = read (fd, buffer, buffer_size);

inotify_rm_watch(wd);

PERL Code Snip

Using Linux::Inotify2, this package also allows the use of (really cool) callback functions on the watch. It's then up to the developer to call poll(), see the Linux::Inotify2 page for more information. This sample takes a more procedural approach.

use Linux::Inotify2;
my $inotify = new Linux::Inotify2();

foreach (@ARGV)
{
  $inotify->watch($_, IN_ALL_EVENTS);
}

while (1)
{
  # By default this will block until something is read
  my @events = $inotify->read();
  if (scalar(@events)==0)
  {
    print "read error: $!";
    last;
  }
  
  foreach (@events)
  {
    printf "File: %s; Mask: %d/n", $_->fullname, $_->mask;
  }

How it works

Inotify is used through a series of system calls specifically created for inotify.

int inotify_init()

Creates an inotify instance. Returns a file descriptor which all events are read from.

int inotify_add_watch(int fd, const char* pathname, int mask)

Starts watching the inode pointed to by pathname for events contained in mask. Returns a watch descriptor which is unique (within this inotify instance) to the inode pointed to by the pathname (NOTE: Multiple pathnames can point to the same inode/watch descriptor).

int inotify_rm_watch(int fd, int wd)

Cancels a watch on the given watch descriptor.

Events generated by inotify contain the following information:

Identifier	Contents
`wd`	watch descriptor
`mask`	event tag
`cookie`	cookie used to synchronize between `IN_MOVED_FROM` and `IN_MOVED_TO`
`len`	length of name field
`name`	the (optional) filename associated with this event (local to parent directory)

Some of the events that can be monitored for are:

IN_ACCESS - read of the file
IN_MODIFY - last modification
IN_ATTRIB - attributes of file change
IN_OPEN and IN_CLOSE - open or close of file
IN_MOVED_FROM and IN_MOVED_TO - when the file is moved or renamed
IN_DELETE - a file/directory deleted
IN_CREATE - a file/directory created
IN_DELETE_SELF - file monitored is deleted

参考：http://fanqiang.chinaunix.net/program/other/2005-05-10/3225.shtml
http://www.qqread.com/linux/2008/10/u435108_3.html
http://www.linuxjournal.com/article/8478
http://blog.csdn.net/absurd/archive/2007/06/18/1656944.aspx
http://blog.chinaunix.net/u/3425/showart_325415.html

QT 中也有相关的类，但要基于系统