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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLES | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVENT_ADD_INOTIFY(3) sd_event_add_inotify SD_EVENT_ADD_INOTIFY(3)
sd_event_add_inotify, sd_event_add_inotify_fd,
sd_event_source_get_inotify_mask,
sd_event_source_get_inotify_path, sd_event_inotify_handler_t -
Add an "inotify" file system inode event source to an event loop
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_inotify_handler_t)(sd_event_source *s,
const struct inotify_event *event,
void *userdata);
int sd_event_add_inotify(sd_event *event,
sd_event_source **source,
const char *path, uint32_t mask,
sd_event_inotify_handler_t handler,
void *userdata);
int sd_event_add_inotify_fd(sd_event *event,
sd_event_source **source, int fd,
uint32_t mask,
sd_event_inotify_handler_t handler,
void *userdata);
int sd_event_source_get_inotify_mask(sd_event_source *source,
uint32_t *ret);
int sd_event_source_get_inotify_path(sd_event_source *source,
const char **ret);
sd_event_add_inotify() adds a new inotify(7) file system inode
event source to an event loop. The event loop object is specified
in the event parameter, the event source object is returned in
the source parameter. The path parameter specifies the path of
the file system inode to watch. The mask parameter specifies
which types of inode events to watch specifically. It must
contain an OR-ed combination of IN_ACCESS, IN_ATTRIB,
IN_CLOSE_WRITE, ... flags. See inotify(7) for further
information.
The handler must reference a function to call when the inode
changes or NULL. The handler function will be passed the userdata
pointer, which may be chosen freely by the caller. The handler
also receives a pointer to a struct inotify_event structure
containing information about the inode event. The handler may
return negative to signal an error (see below), other return
values are ignored. If handler is NULL, a default handler that
calls sd_event_exit(3) will be used.
sd_event_add_inotify_fd() is identical to sd_event_add_inotify(),
except that it takes a file descriptor to an inode (possibly an
O_PATH one, but any other will do too) instead of a path in the
file system.
If multiple event sources are installed for the same inode the
backing inotify watch descriptor is automatically shared. The
mask parameter may contain any flag defined by the inotify API,
with the exception of IN_MASK_ADD.
The handler is enabled continuously (SD_EVENT_ON), but this may
be changed with sd_event_source_set_enabled(3). Alternatively,
the IN_ONESHOT mask flag may be used to request SD_EVENT_ONESHOT
mode. If the handler function returns a negative error code, it
will be disabled after the invocation, even if the SD_EVENT_ON
mode was requested before.
As a special limitation the priority of inotify event sources may
only be altered (see sd_event_source_set_priority(3)) in the time
between creation of the event source object with
sd_event_add_inotify() and the beginning of the next event loop
iteration. Attempts of changing the priority any later will be
refused. Consider freeing and allocating a new inotify event
source to change the priority at that point.
To destroy an event source object use sd_event_source_unref(3),
but note that the event source is only removed from the event
loop when all references to the event source are dropped. To make
sure an event source does not fire anymore, even when there's
still a reference to it kept, consider disabling it with
sd_event_source_set_enabled(3).
If the second parameter of sd_event_add_inotify() is passed as
NULL no reference to the event source object is returned. In this
case the event source is considered "floating", and will be
destroyed implicitly when the event loop itself is destroyed.
If the handler parameter to sd_event_add_inotify() is NULL, and
the event source fires, this will be considered a request to exit
the event loop. In this case, the userdata parameter, cast to an
integer, is passed as the exit code parameter to
sd_event_exit(3).
sd_event_source_get_inotify_mask() retrieves the configured
inotify watch mask of an event source created previously with
sd_event_add_inotify(). It takes the event source object as the
source parameter and a pointer to a uint32_t variable to return
the mask in.
sd_event_source_get_inotify_path() retrieves the target path of
the configured inotify watch of an event source created
previously with sd_event_add_inotify(). It takes the event source
object as the source parameter and a pointer to a const char **
variable to return the path in. The caller must not free the
returned path.
On success, these functions return 0 or a positive integer. On
failure, they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed. This includes specifying
a mask with IN_MASK_ADD set.
-ESTALE
Returned by sd_event_source_add_inotify() or
sd_event_source_add_inotify_fd() when the event loop is
already terminated. Returned by
sd_event_source_get_inotify_path() when no active inode data
is assigned to the event source, e.g. when the event source
is disabled.
-ECHILD
The event loop has been created in a different process,
library or module instance.
-EDOM
The passed event source is not an inotify process event
source.
-EBADF
The passed file descriptor is not valid.
-ENOSYS
sd_event_add_inotify_fd() or
sd_event_source_get_inotify_path() was called without /proc/
mounted.
Example 1. A simple program that uses inotify to monitor one or
two directories
/* SPDX-License-Identifier: MIT-0 */
#include <stdio.h>
#include <string.h>
#include <sys/inotify.h>
#include <systemd/sd-event.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
static int inotify_handler(sd_event_source *source,
const struct inotify_event *event,
void *userdata) {
const char *desc = NULL;
sd_event_source_get_description(source, &desc);
if (event->mask & IN_Q_OVERFLOW)
printf("inotify-handler <%s>: overflow\n", desc);
else if (event->mask & IN_CREATE)
printf("inotify-handler <%s>: create on %s\n", desc, event->name);
else if (event->mask & IN_DELETE)
printf("inotify-handler <%s>: delete on %s\n", desc, event->name);
else if (event->mask & IN_MOVED_TO)
printf("inotify-handler <%s>: moved-to on %s\n", desc, event->name);
/* Terminate the program if an "exit" file appears */
if ((event->mask & (IN_CREATE|IN_MOVED_TO)) &&
strcmp(event->name, "exit") == 0)
sd_event_exit(sd_event_source_get_event(source), 0);
return 1;
}
int main(int argc, char **argv) {
_cleanup_(sd_event_unrefp) sd_event *event = NULL;
_cleanup_(sd_event_source_unrefp) sd_event_source *source1 = NULL, *source2 = NULL;
const char *path1 = argc > 1 ? argv[1] : "/tmp";
const char *path2 = argc > 2 ? argv[2] : NULL;
/* Note: failure handling is omitted for brevity */
sd_event_default(&event);
sd_event_add_inotify(event, &source1, path1,
IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
inotify_handler, NULL);
if (path2)
sd_event_add_inotify(event, &source2, path2,
IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
inotify_handler, NULL);
sd_event_loop(event);
return 0;
}
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
sd_event_inotify_handler_t(), sd_event_add_inotify(), and
sd_event_source_get_inotify_mask() were added in version 239.
sd_event_add_inotify_fd() was added in version 250.
sd_event_source_get_inotify_path() was added in version 256.
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3),
sd_event_add_defer(3), sd_event_add_child(3),
sd_event_source_set_enabled(3), sd_event_source_set_priority(3),
sd_event_source_set_userdata(3),
sd_event_source_set_description(3),
sd_event_source_set_floating(3), waitid(2)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SD_EVENT_ADD_INOTIFY(3)
Pages that refer to this page: sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_memory_pressure(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_new(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_destroy_callback(3), sd_event_source_set_enabled(3), sd_event_source_set_exit_on_failure(3), sd_event_source_set_floating(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_ratelimit(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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