关于Inotify对linux文件系统的监控

Linux提供了hotplup（热插拔），udev和inotify机制帮助我们可以看到底层硬件设备发生了什么，从而能够更好地管理设备，给用户提供更好地服务。

Inotify通过如下三个系统调用和返回的文件描述符上的文件IO操作来使用。

Inotify的使用有如下几个步骤：

1、创建'inotify实例（inotify_init（））

2、添加一个watch（inotify_add_watch（fd,path,mask）） 删除一个watch（inotify_rm_watch（fd，wd））

3、文件事件用一个inotify_event结构表示

struct inotify_event {

__s32 wd; /* watch descriptor */

__u32 mask; /* watch mask */

__u32 cookie; /* cookie to synchronize two event*/

__u32 len; /* length (including nulls) of name */

char name[0]; /* stub for possible name */

};

4、Read调用可以一次获得多个事件size_t len = read（fd，buf，BUF_LEN） 系统内核的实现原理：

每个inotify实例对应一个inotify_device结构：

struct inotify_device { wait_queue_head_t wq; /* wait queue for i/o */

struct idr idr; /* idr mapping wd -> watch */

struct semaphore sem; /* protects this bad boy */

struct list_head events; /* list of queued events */

struct list_head watches; /* list of watches */

atomic_t count; /* reference count */

struct user_struct *user; /* user who opened this dev */

unsigned int queue_size; /* size of the queue (bytes) */

unsigned int event_count; /* number of pending events */

unsigned int max_events; /* maximum number of events */

u32 last_wd; /* the last wd allocated */

};

使用实例：

#include

#include

#include

_syscall0(int, inotify_init)

_syscall3(int, inotify_add_watch, int, fd, const char *, path, __u32, mask)

_syscall2(int, inotify_rm_watch, int, fd, __u32, mask)

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];

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; ifor (i=0; imask & IN_ISDIR) {

memcpy(strbuf, "Direcotory", 11);

}

else {

memcpy(strbuf, "File", 5);

}

printf("Object type: %sn", strbuf);

for (i=0; iwd != wd_array.wd) continue;

printf("Object name: %sn", wd_array.name);

break;

}

printf("Event mask: %08Xn", event->mask);

for (i=0; imask & (1

event = (struct inotify_event *)(offset + tmp_len);

offset += tmp_len;