[PATCH 1/1] inotify.7: add example

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An example for the usage of the inotify API is provided.

It shows the usage of inotify_init1(2),inotify_add_watch(2) as well as
polling and reading form the inotify file descriptor.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
---
 man7/inotify.7 | 226 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 226 insertions(+)

diff --git a/man7/inotify.7 b/man7/inotify.7
index 8e848b2..a422eda 100644
--- a/man7/inotify.7
+++ b/man7/inotify.7
@@ -752,6 +752,232 @@ if the older had not yet been read)
 instead checked if the most recent event could be coalesced with the
 .I oldest
 unread event.
+.SH EXAMPLE
+The following program demonstrates the usage of the inotify API.
+It marks the directories passed as a command-line argument
+and waits for events of type
+.BR IN_OPEN ,
+.BR IN_CLOSE_NOWRITE 
+and
+.BR IN_CLOSE_WRITE .
+.PP
+The following output was recorded while editing the file
+.I /home/user/temp/foo
+and listing directory
+.IR /tmp .
+Before the file and the directory were opened,
+.B IN_OPEN
+events occurred.
+After the file was closed, an
+.B IN_CLOSE_WRITE
+event occurred.
+After the directory was closed, an
+.B IN_CLOSE_NOWRITE
+event occurred.
+Execution of the program ended when the user pressed the ENTER key.
+.SS Example output
+.in +4n
+.nf
+$ ./inotify.7.example /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.
+.fi
+.in
+.SS Program source
+.nf
+#include <errno.h>
+#include <malloc.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/inotify.h>
+#include <unistd.h>
+
+/* Macros for looping over inotify events. */
+
+#define EVENT_LEN ( sizeof (struct inotify_event) )
+#define EVENT_OK(event, len) \\
+	((long)(len) >= (long)EVENT_LEN && \\
+	 (long)(len) >= (long)EVENT_LEN + (long)(event)\->len)
+#define EVENT_NEXT(event, len) \\
+	((len) \-= EVENT_LEN + (event)\->len, \\
+	 (struct inotify_event*)(((char *)(event)) + \\
+	 (event)\->len))
+
+/* 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. */
+
+void
+handle_events(int fd, int *wd, int argc, char* argv[])
+{
+    const struct inotify_event *event;
+    char buf[4096];
+    int i;
+    ssize_t len;
+
+    /* Loop while events can be read from inotify file descriptor. */
+
+    for(;;) {
+
+        /* Read some events. */
+
+        len = read(fd, (void *) &buf, sizeof(buf));
+        if (len == \-1 && errno != EAGAIN) {
+            perror("read");
+            exit(EXIT_FAILURE);
+        }
+
+        /* Check if end of available data reached. */
+
+        if (len <= 0)
+            break;
+
+        /* Point to the first event in the buffer. */
+
+        event = (struct inotify_event *) buf;
+
+        /* Loop over all events in the buffer. */
+
+        while(EVENT_OK(event, len)) {
+
+            /* 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(i = 1; i < argc; ++i) {
+                if(wd[i] == event\->wd)
+                    printf("%s/", argv[i]);
+            }
+
+            /* Print the name of the file. */
+
+            if (event\->len)
+                printf("%s", event\->name);
+
+            /* Print type of file system object. */
+
+            if (event\->mask & IN_ISDIR)
+                printf(" [directory]\\n");
+            else
+                printf(" [file]\\n");
+
+            event = EVENT_NEXT(event, len);
+        }
+    }
+}
+
+int
+main(int argc, char* argv[])
+{
+    char buf;
+    int fd, i, poll_num;
+    int *wd = NULL;
+    nfds_t nfds;
+    struct pollfd fds[2];
+
+    if (argc < 2) {
+        printf("Usage: %s DIRECTORY [DIRECTORY ...]\\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 = (int *) 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) {
+            perror("inotify_add_watch");
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    /* Prepare for polling. */
+
+    nfds = 2;
+
+    /* Console input. */
+
+    fds[0].fd = STDIN_FILENO;
+    fds[0].events = POLLIN;
+
+    /* Inotify input. */
+
+    fds[1].fd = fd;
+    fds[1].events = POLLIN;
+
+    /* This is the loop to wait for incoming events. */
+
+    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);
+            }
+        }
+    }
+
+    /* Close inotify file descriptor. */
+
+    close(fd);
+    free(wd);
+    printf("Listening for events stopped.\\n");
+    return EXIT_SUCCESS;
+}
+.fi
 .SH SEE ALSO
 .BR inotifywait (1),
 .BR inotifywatch (1),
-- 
2.0.0.rc2

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