Add inotify example & client-server socket snippet

inotify.c

@@ -0,0 +1,118 @@
+#include <errno.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/inotify.h>
+#include <unistd.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. */
+    struct inotify_event buf;
+   int i;
+   ssize_t len;
+   char *ptr;
+
+   /* 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;
+       if (buf.mask & IN_CLOSE_WRITE)
+           printf("IN_CLOSE_WRITE: ");
+       /* Print the name of the watched directory */
+       for (i = 1; i < argc; ++i) {
+           if (wd == buf.wd) {
+               printf("%s/", argv[i]);
+               break;
+           }
+       }
+
+       /* Print the name of the file */
+
+       if (buf.len)
+           printf("%s", buf.name);
+
+       /* Print type of filesystem object */
+
+       if (buf.mask & IN_ISDIR)
+           printf(" [directory]\n");
+       else
+           printf(" [file]\n");
+   }
+
+}
+
+int
+main(int argc, char* argv[])
+{
+    int fd, i, poll_num;
+    int wd;
+    struct pollfd fds;
+
+    if (argc != 2) {
+       printf("Usage: %s file\n", argv[0]);
+       exit(EXIT_FAILURE);
+    }
+    fd = inotify_init1(IN_NONBLOCK);
+    if(fd == -1) {
+       perror("inotify_init1");
+       exit(EXIT_FAILURE);
+    }
+    // check if there's a file
+    FILE* f = fopen(argv[1], "r");
+    if(!f){perror("open"); return 1;}
+    char buf[256];
+    if(fread(buf, 1, 256, f) < 1){ perror("read"); return 1;}
+    fclose(f);
+
+    if(-1 == (wd = inotify_add_watch(fd, argv[1], IN_CLOSE_WRITE))){
+        perror("inotify_add_watch");
+        exit(EXIT_FAILURE);
+    }
+    /* Inotify input */
+    fds.fd = fd;
+    fds.events = POLLIN;
+    /* Wait for events */
+    printf("Listening for events.\n");
+    while(1){
+       poll_num = poll(&fds, 1, -1);
+       if(poll_num == -1){
+           if (errno == EINTR)
+               continue;
+           perror("poll");
+           exit(EXIT_FAILURE);
+       }
+       if (poll_num > 0) {
+           if(fds.revents & POLLIN){
+               handle_events(fd, wd, argc, argv);
+           }
+       }
+    }
+    close(fd);
+    exit(EXIT_SUCCESS);
+}