The following program demonstrates the usage of the inotify API.
It marks the directories passed as a command-line arguments and
waits for events of type IN_OPEN, IN_CLOSE_NOWRITE, and
IN_CLOSE_WRITE.
The following output was recorded while editing the file
/home/user/temp/foo and listing directory /tmp. Before the file
and the directory were opened, IN_OPEN events occurred. After
the file was closed, an IN_CLOSE_WRITE event occurred. After the
directory was closed, an IN_CLOSE_NOWRITE event occurred.
Execution of the program ended when the user pressed the ENTER
key.
Example output
$ ./a.out /tmp /home/user/temp
Press enter key to terminate.
Listening for events.
IN_OPEN: /home/user/temp/foo [file]
IN_CLOSE_WRITE: /home/user/temp/foo [file]
IN_OPEN: /tmp/ [directory]
IN_CLOSE_NOWRITE: /tmp/ [directory]
Listening for events stopped.
Program source
#include <errno.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/inotify.h>
#include <unistd.h>
#include <string.h>
/* Read all available inotify events from the file descriptor 'fd'.
wd is the table of watch descriptors for the directories in argv.
argc is the length of wd and argv.
argv is the list of watched directories.
Entry 0 of wd and argv is unused. */
static void
handle_events(int fd, int *wd, int argc, char* argv[])
{
/* Some systems cannot read integer variables if they are not
properly aligned. On other systems, incorrect alignment may
decrease performance. Hence, the buffer used for reading from
the inotify file descriptor should have the same alignment as
struct inotify_event. */
char buf[4096]
__attribute__ ((aligned(__alignof__(struct inotify_event))));
const struct inotify_event *event;
ssize_t len;
/* Loop while events can be read from inotify file descriptor. */
for (;;) {
/* Read some events. */
len = read(fd, buf, sizeof(buf));
if (len == -1 && errno != EAGAIN) {
perror("read");
exit(EXIT_FAILURE);
}
/* If the nonblocking read() found no events to read, then
it returns -1 with errno set to EAGAIN. In that case,
we exit the loop. */
if (len <= 0)
break;
/* Loop over all events in the buffer. */
for (char *ptr = buf; ptr < buf + len;
ptr += sizeof(struct inotify_event) + event->len) {
event = (const struct inotify_event *) ptr;
/* Print event type. */
if (event->mask & IN_OPEN)
printf("IN_OPEN: ");
if (event->mask & IN_CLOSE_NOWRITE)
printf("IN_CLOSE_NOWRITE: ");
if (event->mask & IN_CLOSE_WRITE)
printf("IN_CLOSE_WRITE: ");
/* Print the name of the watched directory. */
for (int i = 1; i < argc; ++i) {
if (wd[i] == event->wd) {
printf("%s/", argv[i]);
break;
}
}
/* Print the name of the file. */
if (event->len)
printf("%s", event->name);
/* Print type of filesystem object. */
if (event->mask & IN_ISDIR)
printf(" [directory]\n");
else
printf(" [file]\n");
}
}
}
int
main(int argc, char* argv[])
{
char buf;
int fd, i, poll_num;
int *wd;
nfds_t nfds;
struct pollfd fds[2];
if (argc < 2) {
printf("Usage: %s PATH [PATH ...]\n", argv[0]);
exit(EXIT_FAILURE);
}
printf("Press ENTER key to terminate.\n");
/* Create the file descriptor for accessing the inotify API. */
fd = inotify_init1(IN_NONBLOCK);
if (fd == -1) {
perror("inotify_init1");
exit(EXIT_FAILURE);
}
/* Allocate memory for watch descriptors. */
wd = calloc(argc, sizeof(int));
if (wd == NULL) {
perror("calloc");
exit(EXIT_FAILURE);
}
/* Mark directories for events
- file was opened
- file was closed */
for (i = 1; i < argc; i++) {
wd[i] = inotify_add_watch(fd, argv[i],
IN_OPEN | IN_CLOSE);
if (wd[i] == -1) {
fprintf(stderr, "Cannot watch '%s': %s\n",
argv[i], strerror(errno));
exit(EXIT_FAILURE);
}
}
/* Prepare for polling. */
nfds = 2;
fds[0].fd = STDIN_FILENO; /* Console input */
fds[0].events = POLLIN;
fds[1].fd = fd; /* Inotify input */
fds[1].events = POLLIN;
/* Wait for events and/or terminal input. */
printf("Listening for events.\n");
while (1) {
poll_num = poll(fds, nfds, -1);
if (poll_num == -1) {
if (errno == EINTR)
continue;
perror("poll");
exit(EXIT_FAILURE);
}
if (poll_num > 0) {
if (fds[0].revents & POLLIN) {
/* Console input is available. Empty stdin and quit. */
while (read(STDIN_FILENO, &buf, 1) > 0 && buf != '\n')
continue;
break;
}
if (fds[1].revents & POLLIN) {
/* Inotify events are available. */
handle_events(fd, wd, argc, argv);
}
}
}
printf("Listening for events stopped.\n");
/* Close inotify file descriptor. */
close(fd);
free(wd);
exit(EXIT_SUCCESS);
}
