Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
+ Lesser General Public License for more details.
- You should have received a copy of the GNU General Public License
+ You should have received a copy of the GNU Lesser General Public License
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-->
actively make changes to the seat configuration,
terminate login sessions, or switch session on a seat
you need to utilize the D-Bus API of
- systemd-logind.</para>
+ systemd-logind, instead.</para>
+
+ <para>These functions synchronously access data in
+ <filename>/proc</filename>,
+ <filename>/sys/fs/cgroup</filename> and
+ <filename>/run</filename>. All of these are virtual
+ file systems, hence the runtime cost of the accesses
+ is relatively cheap.</para>
+
+ <para>It is possible (and often a very good choice) to
+ mix calls to the synchronous interface of
+ <filename>sd-login.h</filename> with the asynchronous
+ D-Bus interface of systemd-logind. However, if this is
+ done you need to think a bit about possible races
+ since the stream of events from D-Bus and from
+ <filename>sd-login.h</filename> interfaces such as the
+ login monitor are asynchronous and not ordered against
+ each other.</para>
+
+ <para>If the functions return string arrays, these are
+ generally NULL terminated and need to be freed by the
+ caller with the libc
+ <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ call after use, including the strings referenced
+ therein. Similar, individual strings returned need to
+ be freed, as well.</para>
+
+ <para>As a special exception, instead of an empty
+ string array NULL may be returned, which should be
+ treated equivalent to an empty string array.</para>
<para>See
<citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,