[리눅스] 간단한 tail -f 구현

http://www.opensource.apple.com/source/text_cmds/text_cmds-9/tail/tail.c

 

출처: http://jangpd007.tistory.com/17

 

kernel 2.6.1 이상이어야 함 이하는 dnotify 사용해야 함

#include <stdio.h>
#include <time.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/inotify.h>

int   exitflag = 1;

int main (int argc, char *argv[])
{
  if (argc == 1)  {
    printf ("tail filename\n");
    return 0;
  }
  char  fname [256];
  sprintf (fname, "%s", argv[1]);
  FILE *fp = fopen (fname, "r");
  if (!fp)  {
    printf ("file(%s)open failed (%d:%s)\n", fname, errno, strerror (errno));
    return 0;
  }

  fseek(fp, 0, SEEK_END);
  int eventfd = inotify_init();
  if (eventfd < 0)  {
    printf ("initial inotify failed (%d:%s)\n", errno, strerror(errno));
    return 0;
  }
  int   wd = 0;
  wd = inotify_add_watch (eventfd, fname, IN_MODIFY|IN_DELETE_SELF|IN_MOVE_SELF);
  if (wd < 0) {
    printf ("add inotify watch failed (%d:%s)\n", errno, strerror(errno));
    return 0;
  }
  while (exitflag)  {
    fd_set  fdset;
    FD_ZERO (&fdset);
    FD_SET (eventfd, &fdset);
    struct  timeval tv;
    tv.tv_sec = 1;
    tv.tv_usec = 0;
    int rc = select ( eventfd + 1, &fdset, (fd_set*)NULL, (fd_set*)NULL, &tv);
    if (rc == 0)  continue;
    if (rc < 0) {
      printf ("select failed (%d:%s)\n", errno, strerror (errno));
      exitflag = 0;
      break;
    }
    if (!FD_ISSET(eventfd, &fdset)) continue;
    char  buff[1024];
    int readlen = read (eventfd, buff, sizeof (buff));
    if (readlen < 0)  {
      printf ("event read failed (%d:%s)\n", errno, strerror(errno));
      exitflag = 0;
      break;
    }
    int eventpos = 0;
    while (eventpos < readlen)  {
      struct  inotify_event *event = ( struct inotify_event*)&buff[eventpos];
      if (event->mask & IN_MODIFY)  {
        char  readbuff[1024];
        if (fgets (readbuff, sizeof (readbuff), fp) == NULL)  continue;
        printf ("%s", readbuff);
      }
      else if (event->mask & IN_DELETE_SELF || event->mask & IN_MOVE_SELF)  {
        printf ("file delete or move event recved\n");
        exitflag = 0;
        break;
      }
      eventpos += (sizeof (struct inotify_event) + event->len);
    }
  }
  inotify_rm_watch (eventfd, wd);
  close (eventfd);
  fclose (fp);
  printf ("normal terminate (exitflag = 0)\n");
  return 0;
}