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.
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)