#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

#include <fcntl.h>

#include <sys/types.h>

#include <sys/event.h>

#include <sys/time.h>

#include <errno.h>

#include <string.h>

#include <inttypes.h>

#define NUM_EVENT_SLOTS 1

#define NUM_EVENT_FDS 1

char *flagstring(int flags);

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

{

    char *path = argv[1];

    int kq;

    int event_fd;

    struct kevent events_to_monitor[NUM_EVENT_FDS];

    struct kevent event_data[NUM_EVENT_SLOTS];

    void *user_data;

    struct timespec timeout;

    unsigned int vnode_events;

    if (argc != 2) {

        fprintf(stderr, "Usage: monitor <file_path>\n");

        exit(-1);

    }

    /* Open a kernel queue. */

    if ((kq = kqueue()) < 0) {

        fprintf(stderr, "Could not open kernel queue.  Error was %s.\n", strerror(errno));

    }

    /*

       Open a file descriptor for the file/directory that you

       want to monitor.

     */

    event_fd = open(path, O_EVTONLY);

    if (event_fd <=0) {

        fprintf(stderr, "The file %s could not be opened for monitoring.  Error was %s.\n", path, strerror(errno));

        exit(-1);

    }

    /*

       The address in user_data will be copied into a field in the

       event.  If you are monitoring multiple files, you could,

       for example, pass in different data structure for each file.

       For this example, the path string is used.

     */

    user_data = path;

    /* Set the timeout to wake us every half second. */

    timeout.tv_sec = 0;        // 0 seconds

    timeout.tv_nsec = 500000000;    // 500 milliseconds

    /* Set up a list of events to monitor. */

    vnode_events = NOTE_DELETE |  NOTE_WRITE | NOTE_EXTEND |                            NOTE_ATTRIB | NOTE_LINK | NOTE_RENAME | NOTE_REVOKE;

    EV_SET( &events_to_monitor[0], event_fd, EVFILT_VNODE, EV_ADD | EV_CLEAR, vnode_events, 0, user_data);

    /* Handle events. */

    int num_files = 1;

    int continue_loop = 40; /* Monitor for twenty seconds. */

    while (--continue_loop) {

        int event_count = kevent(kq, events_to_monitor, NUM_EVENT_SLOTS, event_data, num_files, &timeout);

        if ((event_count < 0) || (event_data[0].flags == EV_ERROR)) {

            /* An error occurred. */

            fprintf(stderr, "An error occurred (event count %d).  The error was %s.\n", event_count, strerror(errno));

            break;

        }

        if (event_count) {

            printf("Event %" PRIdPTR " occurred.  Filter %d, flags %d, filter flags %s, filter data %" PRIdPTR ", path %s\n",

                event_data[0].ident,

                event_data[0].filter,

                event_data[0].flags,

                flagstring(event_data[0].fflags),

                event_data[0].data,

                (char *)event_data[0].udata);

        } else {

            printf("No event.\n");

        }

        /* Reset the timeout.  In case of a signal interrruption, the

           values may change. */

        timeout.tv_sec = 0;        // 0 seconds

        timeout.tv_nsec = 500000000;    // 500 milliseconds

    }

    close(event_fd);

    return 0;

}

/* A simple routine to return a string for a set of flags. */

char *flagstring(int flags)

{

    static char ret[512];

    char *or = "";

    ret[0]='\0'; // clear the string.

    if (flags & NOTE_DELETE) {strcat(ret,or);strcat(ret,"NOTE_DELETE");or="|";}

    if (flags & NOTE_WRITE) {strcat(ret,or);strcat(ret,"NOTE_WRITE");or="|";}

    if (flags & NOTE_EXTEND) {strcat(ret,or);strcat(ret,"NOTE_EXTEND");or="|";}

    if (flags & NOTE_ATTRIB) {strcat(ret,or);strcat(ret,"NOTE_ATTRIB");or="|";}

    if (flags & NOTE_LINK) {strcat(ret,or);strcat(ret,"NOTE_LINK");or="|";}

    if (flags & NOTE_RENAME) {strcat(ret,or);strcat(ret,"NOTE_RENAME");or="|";}

    if (flags & NOTE_REVOKE) {strcat(ret,or);strcat(ret,"NOTE_REVOKE");or="|";}

    return ret;

}