x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
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_unrefp,
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);
void sd_login_monitor_unrefp(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);
DESCRIPTION
sd_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_unrefp() is similar to sd_login_monitor_unref() but
takes a pointer to a pointer to an sd_login_monitor object. This call
is useful in conjunction with GCC's and LLVM's Clean-up Variable
Attribute[1]. Note that this function is defined as inline function.
Use a declaration like the following, in order to allocate a login
monitor object that is freed automatically as the code block is left:
{
__attribute__((cleanup(sd_login_monitor_unrefp))) sd_login_monitor *m = NULL;
int r;
...
r = sd_login_monitor_new(NULL, &m);
if (r < 0) {
errno = -r;
fprintf(stderr, "Failed to allocate login monitor object: %m\n");
}
...
}
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_unref() and sd_login_monitor_unrefp() execute no
operation if the passed in monitor object is NULL.
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 '<mu>s' 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_gettime(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.
Errors
Returned errors may indicate the following problems:
-EINVAL
An input parameter was invalid (out of range, or NULL, where that
is not accepted). The specified category to watch is not known.
-ENOMEM
Memory allocation failed.
NOTES
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.
SEE ALSO
systemd(1), sd-login(3), sd_get_seats(3), poll(2), clock_gettime(2)
NOTES
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
systemd 254 SD_LOGIN_MONITOR_NEW(3)
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