1SD_LOGIN_MONITOR_NEW(3) sd_login_monitor_new SD_LOGIN_MONITOR_NEW(3)
2
6 sd_login_monitor_new, sd_login_monitor_unref, sd_login_monitor_unrefp,
7 sd_login_monitor_flush, sd_login_monitor_get_fd,
8 sd_login_monitor_get_events, sd_login_monitor_get_timeout,
9 sd_login_monitor - Monitor login sessions, seats, users and virtual
10 machines/containers
11
13 #include <systemd/sd-login.h>
14 int sd_login_monitor_new(const char *category, sd_login_monitor **ret);
16 sd_login_monitor *sd_login_monitor_unref(sd_login_monitor *m);
18 void sd_login_monitor_unrefp(sd_login_monitor **m);
20 int sd_login_monitor_flush(sd_login_monitor *m);
22 int sd_login_monitor_get_fd(sd_login_monitor *m);
24 int sd_login_monitor_get_events(sd_login_monitor *m);
26 int sd_login_monitor_get_timeout(sd_login_monitor *m,
28 uint64_t *timeout_usec);
29
31 sd_login_monitor_new() may be used to monitor login sessions, users,
32 seats, and virtual machines/containers. Via a monitor object a file
33 descriptor can be integrated into an application defined event loop
34 which is woken up each time a user logs in, logs out or a seat is added
35 or removed, or a session, user, seat or virtual machine/container
36 changes state otherwise. The first parameter takes a string which can
37 be "seat" (to get only notifications about seats being added, removed
38 or changed), "session" (to get only notifications about sessions being
39 created or removed or changed), "uid" (to get only notifications when a
40 user changes state in respect to logins) or "machine" (to get only
41 notifications when a virtual machine or container is started or
42 stopped). If notifications shall be generated in all these conditions,
43 NULL may be passed. Note that in the future additional categories may
44 be defined. The second parameter returns a monitor object and needs to
45 be freed with the sd_login_monitor_unref() call after use.
46 sd_login_monitor_unref() may be used to destroy a monitor object. Note
48 that this will invalidate any file descriptor returned by
49 sd_login_monitor_get_fd().
50 sd_login_monitor_unrefp() is similar to sd_login_monitor_unref() but
52 takes a pointer to a pointer to an sd_login_monitor object. This call
53 is useful in conjunction with GCC's and LLVM's Clean-up Variable
54 Attribute[1]. Note that this function is defined as inline function.
55 Use a declaration like the following, in order to allocate a login
56 monitor object that is freed automatically as the code block is left:
57 {
59 __attribute__((cleanup(sd_login_monitor_unrefp))) sd_login_monitor *m = NULL;
60 int r;
61 ...
62 r = sd_login_monitor_new(NULL, &m);
63 if (r < 0)
64 fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));
65 ...
66 }
67 sd_login_monitor_flush() may be used to reset the wakeup state of the
69 monitor object. Whenever an event causes the monitor to wake up the
70 event loop via the file descriptor this function needs to be called to
71 reset the wake-up state. If this call is not invoked, the file
72 descriptor will immediately wake up the event loop again.
73 sd_login_monitor_unref() and sd_login_monitor_unrefp() execute no
75 operation if the passed in monitor object is NULL.
76 sd_login_monitor_get_fd() may be used to retrieve the file descriptor
78 of the monitor object that may be integrated in an application defined
79 event loop, based around poll(2) or a similar interface. The
80 application should include the returned file descriptor as wake-up
81 source for the events mask returned by sd_login_monitor_get_events().
82 It should pass a timeout value as returned by
83 sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the
84 file descriptor needs to be reset via sd_login_monitor_flush(). An
85 application needs to reread the login state with a function like
86 sd_get_seats(3) or similar to determine what changed.
87 sd_login_monitor_get_events() will return the poll() mask to wait for.
89 This function will return a combination of POLLIN, POLLOUT and similar
90 to fill into the ".events" field of struct pollfd.
91 sd_login_monitor_get_timeout() will return a timeout value for usage in
93 poll(). This returns a value in microseconds since the epoch of
94 CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
95 clock_gettime(2) for details about CLOCK_MONOTONIC. If there is no
96 timeout to wait for this will fill in (uint64_t) -1 instead. Note that
97 poll() takes a relative timeout in milliseconds rather than an absolute
98 timeout in microseconds. To convert the absolute 'µs' timeout into
99 relative 'ms', use code like the following:
100 uint64_t t;
102 int msec;
103 sd_login_monitor_get_timeout(m, &t);
104 if (t == (uint64_t) -1)
105 msec = -1;
106 else {
107 struct timespec ts;
108 uint64_t n;
109 clock_gettime(CLOCK_MONOTONIC, &ts);
110 n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
111 msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
112 }
113 The code above does not do any error checking for brevity's sake. The
115 calculated msec integer can be passed directly as poll()'s timeout
116 parameter.
117
119 On success, sd_login_monitor_new(), sd_login_monitor_flush() and
120 sd_login_monitor_get_timeout() return 0 or a positive integer. On
121 success, sd_login_monitor_get_fd() returns a Unix file descriptor. On
122 success, sd_login_monitor_get_events() returns a combination of POLLIN,
123 POLLOUT and suchlike. On failure, these calls return a negative
124 errno-style error code.
125 sd_login_monitor_unref() always returns NULL.
127 Errors
129 Returned errors may indicate the following problems:
130 -EINVAL
132 An input parameter was invalid (out of range, or NULL, where that
133 is not accepted). The specified category to watch is not known.
134 -ENOMEM
136 Memory allocation failed.
137
139 These APIs are implemented as a shared library, which can be compiled
140 and linked to with the libsystemd pkg-config(1) file.
141
143 systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)
144
146 1. Clean-up Variable Attribute
147 https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
148systemd 251 SD_LOGIN_MONITOR_NEW(3)