Hi Heinrich,
On 05/22/2014 08:03 PM, Heinrich Schuchardt wrote:
> This third version of the patch considers comments by Michael Kerrisk
> concerning
>
> * alignment of inotify read buffer
>
> On some systems integer values can only be read if they are
> correctly aligned. Other system have a lower performance when
> reading from or writing to misaligned memory positions.
> An array of struct inotify_event is used to have the buffer
> properly aligned. As on ILP64 systems int is 8 byte long
> using aligned(4) may not be sufficient.
>
> * simplification of loop over inotify event buffer
>
> * typos
Thanks for the update. Two questions below.
>
> ***
>
> 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 from the inotify file descriptor.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> ---
> man7/inotify.7 | 221 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 220 insertions(+), 1 deletion(-)
>
> diff --git a/man7/inotify.7 b/man7/inotify.7
> index 8e848b2..2f21945 100644
> --- a/man7/inotify.7
> +++ b/man7/inotify.7
> @@ -1,5 +1,6 @@
> '\" t
> .\" Copyright (C) 2006, 2014 Michael Kerrisk <mtk.manpages@xxxxxxxxx>
> +.\" Copyright (C) 2014 Heinrich Schuchardt <xypron.glpk@xxxxxx>
> .\"
> .\" %%%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 +753,224 @@ 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[])
> +{
> + struct inotify_event buf[200];
This works fine for fanotify, but with inotify_event, there is a
small snag. Because of the variable length 'name' field at the
end of the structure, 'gcc -Wpedantic' gives the warning:
"invalid use of structure with flexible array member".
I'm not keen on example programs that generate warnings,
so, I'd be a bit more happier with either
char buf[BUF_LEN]
__attribute__ ((aligned(__alignof__(struct inotify_event))));
or
char buf[BUF_LEN]__attribute__ ((aligned(__alignof__(8))));
> + 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 = (char *) buf; ptr < (char *) 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 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 = 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);
Earlier, I commented on the above, but you didn't (as far as
I can see) respond.I n the Usage message, you specify the
arguments as directories. So, should you by using IN_ONLYDIR
here?
> + 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),
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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