c - 使用daemon和inotify在C中制作一个文件监视器

Question

我正在使用 daemon 和 inotify 来监视文件。我不知道我的代码发生了什么。如果我使用 inotify_add_watch 来监视目录，它就可以工作。但它不适用于单个文件。如果您有任何想法，请帮助我。我认为问题出在 read() 部分。系统似乎无法将文件读入缓冲区。但我不太确定。 TIA。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <syslog.h>
#include <errno.h>

#include <linux/inotify.h>

#define EVENT_SIZE (sizeof (struct inotify_event))
#define EVENT_BUF_LEN (1024 * (EVENT_SIZE + 16))

静态无效 Skeleton_daemon(){

pid_t pid;

/* Fork off the parent process */
pid = fork();

/* An error occurred */
if (pid < 0){
    //printf("pid<0 error");
    exit(EXIT_FAILURE);
}
/* Success: Let the parent terminate */
if (pid > 0){
    //printf("pid>0 parent terminate");
    exit(EXIT_SUCCESS);
}

/* On success: The child process becomes session leader */
if (setsid() < 0){
    //printf("setsid <0");
    exit(EXIT_FAILURE);
}

/* Catch, ignore and handle signals */
//TODO: Implement a working signal handler */
signal(SIGCHLD, SIG_IGN);
signal(SIGHUP, SIG_IGN);

/* Fork off for the second time*/
pid = fork();

/* An error occurred */
if (pid < 0){
    //printf("pid<0");
    exit(EXIT_FAILURE);
}
/* Success: Let the parent terminate */
if (pid > 0){
    //printf("pid > 0 ");
    exit(EXIT_SUCCESS);
}
/* Set new file permissions */
umask(0);

/* Change the working directory to the root directory */
/* or another appropriated directory */
chdir("/");

/* Close all open file descriptors */
int x;
for (x = sysconf(_SC_OPEN_MAX); x>0; x--)
{
    close (x);
}

/* Open the log file */
openlog ("firstdaemon", LOG_PID, LOG_DAEMON);

}

int main(int argc, char *argv[] ){

int length, i = 0;

int fd;

int wd;

char buffer[EVENT_BUF_LEN];

skeleton_daemon();

//printf("the argv[] after daemon is %s",argv[1]);

syslog (LOG_NOTICE, "------------  First testing daemon started.----------");

/*creating the INOTIFY instance*/
fd = inotify_init();

/*checking for error*/
if ( fd < 0 ) {
  perror( "inotify_init" );
}

/*adding the directory into watch list. */
wd = inotify_add_watch( fd,  "/home/temp/test"    , IN_ALL_EVENTS  /* IN_IGNORED | IN_OPEN | IN_CLOSE_WRITE | IN_ATTRIB | IN_CREATE | IN_DELETE |IN_CLOSE | IN_MODIFY | IN_ACCESS */ );

if(wd<0){
syslog(LOG_NOTICE, "wd < 0");
perror("inotify_add_watch");    
}

//syslog(LOG_NOTICE, "THE FILE WE ARE MONITORING IS: %s",argv[1]);

while (1)
{
    //TODO: Insert daemon code here.

syslog (LOG_NOTICE, "~~~~~~~ One new testing daemon started.~~~~~~~~~");    

/*read to determine the event change happens on directory. Actually this read blocks until the change event occurs*/
    syslog (LOG_NOTICE, "BEFORE READ IN BUFFER");
    length = read( fd, buffer, EVENT_BUF_LEN );

syslog (LOG_NOTICE, "AFTER READ IN BUFFER.");

    /*checking for error*/
    if ( length < 0 ) {
      perror( "read" );
    }else if(length == 0){
    syslog(LOG_NOTICE," length =0 " );
    continue;
}

/*actually read return the list of change events happens. Here, read the change event one by one and process it accordingly.*/
while ( i < length ) {     
    struct inotify_event *event = ( struct inotify_event * ) &buffer[ i ];     
    if ( event->len ) {

    if (event->mask & IN_IGNORED) {
            inotify_rm_watch(fd,wd);
            inotify_add_watch(fd,"/home/test", IN_ALL_EVENTS );
        }       

    if ( event->mask & IN_ATTRIB ) {
                if ( event->mask & IN_ISDIR ) {
                    //printf( " directory %s ATTRIB .\n", event->name );
        syslog (LOG_NOTICE, " directory:chaning     ATTRIB .");
                    syslog (LOG_NOTICE, " directory:%s ATTRIB .", event->name);
                }   
                else {
        syslog (LOG_NOTICE, " directory:chaning     ATTRIB .");

                    syslog (LOG_NOTICE, " file:%s ATTRIB .", event->name);                            
                }   
            }  

    if ( event->mask & IN_MODIFY ) {
               if ( event->mask & IN_ISDIR ) {
                    //printf( " directory %s modified .\n", event->name );
        syslog (LOG_NOTICE, " dirtory:chaning    !!!!!!! .");
                    syslog (LOG_NOTICE, " file:%s modify.", event->name);
                }
                else {
        syslog (LOG_NOTICE, " file  modify:chaning!!! .");

                    syslog (LOG_NOTICE, " file:%s modify.", event->name);
                }
            }

    if ( event->mask & IN_CLOSE_WRITE ) {
                if ( event->mask & IN_ISDIR ) {
                    //printf( " directory %s modified .\n", event->name );
                    syslog (LOG_NOTICE, " CLSOE WRITE    !!!!!!! .");
                    //syslog (LOG_NOTICE, " file:%s modify.", event->name);
                }
                else {
                    //syslog (LOG_NOTICE, " file modify:changing!!! .");
                syslog (LOG_NOTICE, " CLSOE WRITE    !!!!!!! .");                   
                    //syslog (LOG_NOTICE, " file:%s modify.", event->name);
                }
            }

    if ( event->mask & IN_OPEN ) {
                if ( event->mask & IN_ISDIR ) {
                    //printf( "New directory %s opened.\n", event->name );
                    syslog (LOG_NOTICE, " directory:%s open.", event->name);
                }
                else {
        syslog (LOG_NOTICE, " file:opening.");

                    syslog (LOG_NOTICE, " file:%s open.", event->name);
                    //printf( "New file %s open.\n", event->name );

                }
            }

        if ( event->mask & IN_CREATE ) {
        if ( event->mask & IN_ISDIR ) {
            //printf( "New directory %s created.\n", event->name );
            syslog (LOG_NOTICE, "new directory:%s created.", event->name);
        }
        else {
            syslog (LOG_NOTICE, "new file:%s created.", event->name);
            //printf( "New file %s created.\n", event->name );

            }
        }
        else if ( event->mask & IN_DELETE ) {
        if ( event->mask & IN_ISDIR ) {
            syslog (LOG_NOTICE, "dir:%s is deleted.", event->name);
            //printf( "Directory %s deleted.\n", event->name );
        }
        else {
            syslog (LOG_NOTICE, "file:%s is deleted.", event->name);
            //printf( "File %s deleted.\n", event->name );
        }
        }

    else if ( event->mask & IN_ACCESS ) {
                if ( event->mask & IN_ISDIR ) {
                    syslog(LOG_NOTICE, "dir:%s is accessed.", event->name);
                    //printf( "The directory %s was accessed.\n", event->name );
                }
                else {
                    syslog(LOG_NOTICE, "file:%s is accessed.", event->name);
                    //printf( "The file %s was accessed.\n", event->name );
                }   
            } 

    if ( event->mask & IN_CLOSE ) {
                if ( event->mask & IN_ISDIR ) {
                    //printf( "New directory %s created.\n", event->name );
                    syslog (LOG_NOTICE, " directory:%s closed.", event->name);
                }
                else {
                    syslog (LOG_NOTICE, " file:%s closed.", event->name);
                    //printf( "New file %s created.\n", event->name );

                }
            }

        }
    i += EVENT_SIZE + event->len;
}

    i=0;    
syslog (LOG_NOTICE, "~~~~~~one testing daemon ended.~~~~~~~~~~");
    sleep (20);
}

/*removing the directory from the watch list.*/
inotify_rm_watch( fd, wd );

/*closing the INOTIFY instance*/
close( fd );

syslog (LOG_NOTICE, "--------------- first testing daemon terminated.----------------");
closelog();

return EXIT_SUCCESS;

}

Answer 1

您的代码中的问题是这样的:

if ( event->len )

来自 inotify 文档:

The name field is present only when an event is returned for a file inside a watched directory; it identifies the file pathname relative to the watched directory.

对于涉及为单个文件添加的监视的事件，event->len 的值为零。因此，其余代码永远不会执行。