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 errno = -r;
65 fprintf(stderr, "Failed to allocate login monitor object: %m\n");
66 }
67 ...
68 }
69 sd_login_monitor_flush() may be used to reset the wakeup state of the
71 monitor object. Whenever an event causes the monitor to wake up the
72 event loop via the file descriptor this function needs to be called to
73 reset the wake-up state. If this call is not invoked, the file
74 descriptor will immediately wake up the event loop again.
75 sd_login_monitor_unref() and sd_login_monitor_unrefp() execute no
77 operation if the passed in monitor object is NULL.
78 sd_login_monitor_get_fd() may be used to retrieve the file descriptor
80 of the monitor object that may be integrated in an application defined
81 event loop, based around poll(2) or a similar interface. The
82 application should include the returned file descriptor as wake-up
83 source for the events mask returned by sd_login_monitor_get_events().
84 It should pass a timeout value as returned by
85 sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the
86 file descriptor needs to be reset via sd_login_monitor_flush(). An
87 application needs to reread the login state with a function like
88 sd_get_seats(3) or similar to determine what changed.
89 sd_login_monitor_get_events() will return the poll() mask to wait for.
91 This function will return a combination of POLLIN, POLLOUT and similar
92 to fill into the ".events" field of struct pollfd.
93 sd_login_monitor_get_timeout() will return a timeout value for usage in
95 poll(). This returns a value in microseconds since the epoch of
96 CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
97 clock_gettime(2) for details about CLOCK_MONOTONIC. If there is no
98 timeout to wait for this will fill in (uint64_t) -1 instead. Note that
99 poll() takes a relative timeout in milliseconds rather than an absolute
100 timeout in microseconds. To convert the absolute 'μs' timeout into
101 relative 'ms', use code like the following:
102 uint64_t t;
104 int msec;
105 sd_login_monitor_get_timeout(m, &t);
106 if (t == (uint64_t) -1)
107 msec = -1;
108 else {
109 struct timespec ts;
110 uint64_t n;
111 clock_gettime(CLOCK_MONOTONIC, &ts);
112 n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
113 msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
114 }
115 The code above does not do any error checking for brevity's sake. The
117 calculated msec integer can be passed directly as poll()'s timeout
118 parameter.
119
121 On success, sd_login_monitor_new(), sd_login_monitor_flush() and
122 sd_login_monitor_get_timeout() return 0 or a positive integer. On
123 success, sd_login_monitor_get_fd() returns a Unix file descriptor. On
124 success, sd_login_monitor_get_events() returns a combination of POLLIN,
125 POLLOUT and suchlike. On failure, these calls return a negative
126 errno-style error code.
127 sd_login_monitor_unref() always returns NULL.
129 Errors
131 Returned errors may indicate the following problems:
132 -EINVAL
134 An input parameter was invalid (out of range, or NULL, where that
135 is not accepted). The specified category to watch is not known.
136 -ENOMEM
138 Memory allocation failed.
139
141 Functions described here are available as a shared library, which can
142 be compiled against and linked to with the libsystemd pkg-config(1)
143 file.
144 The code described here uses getenv(3), which is declared to be not
146 multi-thread-safe. This means that the code calling the functions
147 described here must not call setenv(3) from a parallel thread. It is
148 recommended to only do calls to setenv() from an early phase of the
149 program when no other threads have been started.
150
152 systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)
153
155 1. Clean-up Variable Attribute
156 https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
157systemd 254 SD_LOGIN_MONITOR_NEW(3)