sd_event_inotify_handler_t(3)

1SD_EVENT_ADD_INOTIFY(3)      sd_event_add_inotify      SD_EVENT_ADD_INOTIFY(3)
2
3
4

NAME

6       sd_event_add_inotify, sd_event_add_inotify_fd,
7       sd_event_source_get_inotify_mask, sd_event_inotify_handler_t - Add an
8       "inotify" file system inode event source to an event loop
9

SYNOPSIS

11       #include <systemd/sd-event.h>
12
13       typedef struct sd_event_source sd_event_source;
14
15       typedef int (*sd_event_inotify_handler_t)(sd_event_source *s,
16                                                 const struct inotify_event *event,
17                                                 void *userdata);
18
19       int sd_event_add_inotify(sd_event *event, sd_event_source **source,
20                                const char *path, uint32_t mask,
21                                sd_event_inotify_handler_t handler,
22                                void *userdata);
23
24       int sd_event_add_inotify_fd(sd_event *event, sd_event_source **source,
25                                   int fd, uint32_t mask,
26                                   sd_event_inotify_handler_t handler,
27                                   void *userdata);
28
29       int sd_event_source_get_inotify_mask(sd_event_source *source,
30                                            uint32_t *mask);
31

DESCRIPTION

33       sd_event_add_inotify() adds a new inotify(7) file system inode event
34       source to an event loop. The event loop object is specified in the
35       event parameter, the event source object is returned in the source
36       parameter. The path parameter specifies the path of the file system
37       inode to watch. The mask parameter specifies which types of inode
38       events to watch specifically. It must contain an OR-ed combination of
39       IN_ACCESS, IN_ATTRIB, IN_CLOSE_WRITE, ... flags. See inotify(7) for
40       further information.
41
42       The handler must reference a function to call when the inode changes or
43       NULL. The handler function will be passed the userdata pointer, which
44       may be chosen freely by the caller. The handler also receives a pointer
45       to a struct inotify_event structure containing information about the
46       inode event. The handler may return negative to signal an error (see
47       below), other return values are ignored. If handler is NULL, a default
48       handler that calls sd_event_exit(3) will be used.
49
50       sd_event_add_inotify_fd() is identical to sd_event_add_inotify(),
51       except that it takes a file descriptor to an inode (possibly an O_PATH
52       one, but any other will do too) instead of a path in the file system.
53
54       If multiple event sources are installed for the same inode the backing
55       inotify watch descriptor is automatically shared. The mask parameter
56       may contain any flag defined by the inotify API, with the exception of
57       IN_MASK_ADD.
58
59       The handler is enabled continuously (SD_EVENT_ON), but this may be
60       changed with sd_event_source_set_enabled(3). Alternatively, the
61       IN_ONESHOT mask flag may be used to request SD_EVENT_ONESHOT mode. If
62       the handler function returns a negative error code, it will be disabled
63       after the invocation, even if the SD_EVENT_ON mode was requested
64       before.
65
66       As a special limitation the priority of inotify event sources may only
67       be altered (see sd_event_source_set_priority(3)) in the time between
68       creation of the event source object with sd_event_add_inotify() and the
69       beginning of the next event loop iteration. Attempts of changing the
70       priority any later will be refused. Consider freeing and allocating a
71       new inotify event source to change the priority at that point.
72
73       To destroy an event source object use sd_event_source_unref(3), but
74       note that the event source is only removed from the event loop when all
75       references to the event source are dropped. To make sure an event
76       source does not fire anymore, even when there's still a reference to it
77       kept, consider disabling it with sd_event_source_set_enabled(3).
78
79       If the second parameter of sd_event_add_inotify() is passed as NULL no
80       reference to the event source object is returned. In this case the
81       event source is considered "floating", and will be destroyed implicitly
82       when the event loop itself is destroyed.
83
84       If the handler parameter to sd_event_add_inotify() is NULL, and the
85       event source fires, this will be considered a request to exit the event
86       loop. In this case, the userdata parameter, cast to an integer, is
87       passed as the exit code parameter to sd_event_exit(3).
88
89       sd_event_source_get_inotify_mask() retrieves the configured inotify
90       watch mask of an event source created previously with
91       sd_event_add_inotify(). It takes the event source object as the source
92       parameter and a pointer to a uint32_t variable to return the mask in.
93

RETURN VALUE

95       On success, these functions return 0 or a positive integer. On failure,
96       they return a negative errno-style error code.
97
98   Errors
99       Returned errors may indicate the following problems:
100
101       -ENOMEM
102           Not enough memory to allocate an object.
103
104       -EINVAL
105           An invalid argument has been passed. This includes specifying a
106           mask with IN_MASK_ADD set.
107
108       -ESTALE
109           The event loop is already terminated.
110
111       -ECHILD
112           The event loop has been created in a different process.
113
114       -EDOM
115           The passed event source is not an inotify process event source.
116
117       -EBADF
118           The passed file descriptor is not valid.
119
120       -ENOSYS
121           sd_event_add_inotify_fd() was called without /proc/ mounted.
122

EXAMPLES

124       Example 1. A simple program that uses inotify to monitor one or two
125       directories
126
127           /* SPDX-License-Identifier: MIT-0 */
128
129           #include <stdio.h>
130           #include <string.h>
131           #include <sys/inotify.h>
132
133           #include <systemd/sd-event.h>
134
135           #define _cleanup_(f) __attribute__((cleanup(f)))
136
137           static int inotify_handler(sd_event_source *source,
138                                      const struct inotify_event *event,
139                                      void *userdata) {
140
141             const char *desc = NULL;
142
143             sd_event_source_get_description(source, &desc);
144
145             if (event->mask & IN_Q_OVERFLOW)
146               printf("inotify-handler <%s>: overflow\n", desc);
147             else if (event->mask & IN_CREATE)
148               printf("inotify-handler <%s>: create on %s\n", desc, event->name);
149             else if (event->mask & IN_DELETE)
150               printf("inotify-handler <%s>: delete on %s\n", desc, event->name);
151             else if (event->mask & IN_MOVED_TO)
152               printf("inotify-handler <%s>: moved-to on %s\n", desc, event->name);
153
154             /* Terminate the program if an "exit" file appears */
155             if ((event->mask & (IN_CREATE|IN_MOVED_TO)) &&
156                 strcmp(event->name, "exit") == 0)
157               sd_event_exit(sd_event_source_get_event(source), 0);
158
159             return 1;
160           }
161
162           int main(int argc, char **argv) {
163             _cleanup_(sd_event_unrefp) sd_event *event = NULL;
164             _cleanup_(sd_event_source_unrefp) sd_event_source *source1 = NULL, *source2 = NULL;
165
166             const char *path1 = argc > 1 ? argv[1] : "/tmp";
167             const char *path2 = argc > 2 ? argv[2] : NULL;
168
169             /* Note: failure handling is omitted for brevity */
170
171             sd_event_default(&event);
172
173             sd_event_add_inotify(event, &source1, path1,
174                                  IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
175                                  inotify_handler, NULL);
176             if (path2)
177               sd_event_add_inotify(event, &source2, path2,
178                                    IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
179                                    inotify_handler, NULL);
180
181             sd_event_loop(event);
182
183             return 0;
184           }
185

NOTES

187       These APIs are implemented as a shared library, which can be compiled
188       and linked to with the libsystemd pkg-config(1) file.
189

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

EXAMPLES

NOTES

SEE ALSO