NetBSDのfilemon機能を利用してファイル書き込みイベントをハンドリングするサンプルです。

nbsd_filemon_watch_write_event.c

/*
 * NetBSD filemonのファイル書き込みの監視サンプル。
 *
 *   $ gcc -Wall -Werror -g -o nbsd_filemon_watch_write_event nbsd_filemon_watch_write_event.c
 */

#include <dev/filemon/filemon.h>

#include <sys/wait.h>
#include <sys/ioctl.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <unistd.h>

extern char *optarg;
extern int optind;

int main(int argc, char *argv[])
{
    int ch;
    char *w_cmd = NULL;  // open(RDWR)
    
    while ((ch = getopt(argc, argv, "w:")) != -1) {
        switch (ch) {
            case 'w': w_cmd = optarg; break;
            case '?':
            default:
                break;
        }
    }
    argc -= optind;
    argv += optind;

#if DEBUG
    if (w_cmd) printf("W: open(RDWR)   %s\n", w_cmd);
#endif

    pid_t pid;
    int filemon_fd, temp_fd;
    int status;
    char temp_path[] = "/tmp/filemonXXXXXXXX";

    FILE *fp = NULL;
    char buf[BUFSIZ];
    int read_line = 0;
    int count = 0;
    int is_done = 0;

    filemon_fd = open("/dev/filemon", O_RDWR);
    temp_fd = mkstemp(temp_path);

    // give filemon the temp file to use
    ioctl(filemon_fd, FILEMON_SET_FD, &temp_fd);

    // children do not need these one they exec
    fcntl(filemon_fd, F_SETFD, FD_CLOEXEC);
    fcntl(temp_fd, F_SETFD, FD_CLOEXEC);

    pid = fork();
    switch(pid) {
        case -1:
            fprintf(stderr, "cannot fork");
            break;
        case 0:
            printf("filemon: %s\n", temp_path);
            pid = getpid();
            // tell filemon to monitor this process
            ioctl(filemon_fd, FILEMON_SET_PID, &pid);
            execvp(argv[0], argv);
            _exit(1);

            break;
        default:
           lseek(temp_fd, SEEK_SET, 0);

           is_done = 1;
           while (is_done) {
               fp = fopen(temp_path, "r");
               if (fp) {
                   count = 0;
                   while (fgets(buf, BUFSIZ-1, fp)) {
                       if (count++ < read_line) {
                           continue;
                       }

                       if (buf[0] == 'W') {
                           // "W 521 cal.txt" => "cal.txt"
                           char *path = strchr(buf, ' ');
                           path = strchr(++path, ' ');
                           ++path;

                           switch(fork()) {
                                case -1:
                                    fprintf(stderr, "cannot fork");
                                    break;
                                case 0:
                                    if (w_cmd) {
                                        char *script[] = { w_cmd, path, NULL };
                                        execvp(script[0], script);
                                    }
                                default:
                                    wait(&status);
                           }
                       }
                       if (buf[0] == '#') {
                           is_done = 0;
                           break;
                       }
                   }
                   read_line += count - read_line;

                   fclose(fp);
                   usleep(700000);
               }
           }

           wait(&status);
           close(filemon_fd);
           close(temp_fd);

           break;
    }

    return 0;
}