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inotify.7: Add example program 

This example of the usage of the inotify API shows the
usage of inotify_init1(2) and inotify_add_watch(2) as well
as polling and reading from the inotify file descriptor.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Heinrich Schuchardt 2014-05-24 22:02:13 +02:00 committed by Michael Kerrisk
parent 9fb49a3a80
commit ecd96f7c0e
1 changed files with 227 additions and 1 deletions
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man7/inotify.7
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@ -1,5 +1,6 @@
'\" t
.\" Copyright (C) 2006, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright (C) 2014 Heinrich Schuchardt <xypron.glpk@gmx.de>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
@ -23,7 +24,7 @@
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH INOTIFY 7 2014-05-08 "Linux" "Linux Programmer's Manual"
.TH INOTIFY 7 2014-05-23 "Linux" "Linux Programmer's Manual"
.SH NAME
inotify \- monitoring filesystem events
.SH DESCRIPTION
@ -752,6 +753,231 @@ 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 arguments
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 <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. */
char buf[4096]
__attribute__ ((aligned(__alignof__(struct inotify_event))));
const struct inotify_event *event;
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;
/* Loop over all events in the buffer */
for (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 (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'\\n", argv[i]);
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;
/* 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);
}
}
}
/* Close inotify file descriptor */
close(fd);
free(wd);
printf("Listening for events stopped.\\n");
exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR inotifywait (1),
.BR inotifywatch (1),