SD_LOGIN_MONITOR_NEW(3) sd_login_monitor_new SD_LOGIN_MONITOR_NEW(3)NAME
sd_login_monitor_new, sd_login_monitor_unref, sd_login_monitor_flush,
sd_login_monitor_get_fd, sd_login_monitor_get_events,
sd_login_monitor_get_timeout, sd_login_monitor - Monitor login
sessions, seats, users and virtual machines/containers
SYNOPSIS
#include <systemd/sd-login.h>
int sd_login_monitor_new(const char* category, sd_login_monitor** ret);
sd_login_monitor* sd_login_monitor_unref(sd_login_monitor* m);
int sd_login_monitor_flush(sd_login_monitor* m);
int sd_login_monitor_get_fd(sd_login_monitor* m);
int sd_login_monitor_get_events(sd_login_monitor* m);
int sd_login_monitor_get_timeout(sd_login_monitor* m,
uint64_t* timeout_usec);
DESCRIPTIONsd_login_monitor_new() may be used to monitor login sessions, users,
seats, and virtual machines/containers. Via a monitor object a file
descriptor can be integrated into an application defined event loop
which is woken up each time a user logs in, logs out or a seat is added
or removed, or a session, user, seat or virtual machine/container
changes state otherwise. The first parameter takes a string which can
be "seat" (to get only notifications about seats being added, removed
or changed), "session" (to get only notifications about sessions being
created or removed or changed), "uid" (to get only notifications when a
user changes state in respect to logins) or "machine" (to get only
notifications when a virtual machine or container is started or
stopped). If notifications shall be generated in all these conditions,
NULL may be passed. Note that in the future additional categories may
be defined. The second parameter returns a monitor object and needs to
be freed with the sd_login_monitor_unref() call after use.
sd_login_monitor_unref() may be used to destroy a monitor object. Note
that this will invalidate any file descriptor returned by
sd_login_monitor_get_fd().
sd_login_monitor_flush() may be used to reset the wakeup state of the
monitor object. Whenever an event causes the monitor to wake up the
event loop via the file descriptor this function needs to be called to
reset the wake-up state. If this call is not invoked, the file
descriptor will immediately wake up the event loop again.
sd_login_monitor_get_fd() may be used to retrieve the file descriptor
of the monitor object that may be integrated in an application defined
event loop, based around poll(2) or a similar interface. The
application should include the returned file descriptor as wake-up
source for the events mask returned by sd_login_monitor_get_events().
It should pass a timeout value as returned by
sd_login_monitor_get_timeout(). Whenever a wake-up is triggered the
file descriptor needs to be reset via sd_login_monitor_flush(). An
application needs to reread the login state with a function like
sd_get_seats(3) or similar to determine what changed.
sd_login_monitor_get_events() will return the poll() mask to wait for.
This function will return a combination of POLLIN, POLLOUT and similar
to fill into the ".events" field of struct pollfd.
sd_login_monitor_get_timeout() will return a timeout value for usage in
poll(). This returns a value in microseconds since the epoch of
CLOCK_MONOTONIC for timing out poll() in timeout_usec. See
clock_gettime(2) for details about CLOCK_MONOTONIC. If there is no
timeout to wait for this will fill in (uint64_t) -1 instead. Note that
poll() takes a relative timeout in milliseconds rather than an absolute
timeout in microseconds. To convert the absolute 'us' timeout into
relative 'ms', use code like the following:
uint64_t t;
int msec;
sd_login_monitor_get_timeout(m, &t);
if (t == (uint64_t) -1)
msec = -1;
else {
struct timespec ts;
uint64_t n;
clock_getttime(CLOCK_MONOTONIC, &ts);
n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
}
The code above does not do any error checking for brevity's sake. The
calculated msec integer can be passed directly as poll()'s timeout
parameter.
RETURN VALUE
On success sd_login_monitor_new(), sd_login_monitor_flush() and
sd_login_monitor_get_timeout() return 0 or a positive integer. On
success sd_login_monitor_get_fd() returns a Unix file descriptor. On
success sd_login_monitor_get_events() returns a combination of POLLIN,
POLLOUT and suchlike. On failure, these calls return a negative
errno-style error code.
sd_login_monitor_unref() always returns NULL.
NOTES
The sd_login_monitor_new(), sd_login_monitor_unref(),
sd_login_monitor_flush(), sd_login_monitor_get_fd(),
sd_login_monitor_get_events() and sd_login_monitor_get_timeout()
interfaces are available as shared library, which can be compiled and
linked to with the libsystemd-login pkg-config(1) file.
SEE ALSOsystemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)systemd 208SD_LOGIN_MONITOR_NEW(3)