login: add sd_login_monitor_get_timeout() public api call

We don't need this right now, but we should keep our options open, in
case we need more than just an fd for waking up.

1 files changed, 54 insertions, 7 deletions

diff --git a/man/sd_login_monitor_new.xml b/man/sd_login_monitor_new.xml
index 94428771a..b187ad0db 100644
--- a/man/sd_login_monitor_new.xml
+++ b/man/sd_login_monitor_new.xml
@@ -48,6 +48,7 @@
                 <refname>sd_login_monitor_flush</refname>
                 <refname>sd_login_monitor_get_fd</refname>
                 <refname>sd_login_monitor_get_events</refname>
+                <refname>sd_login_monitor_get_timeout</refname>
                 <refname>sd_login_monitor</refname>
                 <refpurpose>Monitor login sessions, seats and users</refpurpose>
         </refnamediv>
@@ -82,6 +83,12 @@
                                 <paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
                         </funcprototype>
 
+                        <funcprototype>
+                                <funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
+                                <paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
+                                <paramdef>uint64_t* <parameter>timeout_usec</parameter></paramdef>
+                        </funcprototype>
+
                 </funcsynopsis>
         </refsynopsisdiv>
 
@@ -130,7 +137,9 @@
                 or a similar interface. The application should include
                 the returned file descriptor as wake-up source for the
                 events mask returned by
-                <function>sd_login_monitor_get_events()</function>. Whenever
+                <function>sd_login_monitor_get_events()</function>. It
+                should pass a timeout value as returned by
+                <function>sd_login_monitor_get_timeout()</function>. Whenever
                 a wake-up is triggered the file descriptor needs to be
                 reset via
                 <function>sd_login_monitor_flush()</function>. An
@@ -146,15 +155,51 @@
                 and similar to fill into the
                 <literal>.events</literal> field of <literal>struct
                 pollfd</literal>.</para>
+
+                <para><function>sd_login_monitor_get_timeout()</function>
+                will return a timeout value for usage in
+                <function>poll()</function>. This returns a value in
+                microseconds since the epoch of CLOCK_MONOTONIC for
+                timing out <function>poll()</function> in
+                <literal>timeout_usec</literal>. See
+                <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+                for details about
+                <literal>CLOCK_MONOTONIC</literal>. If there's no
+                timeout to wait for this will fill in
+                <literal>(uint64_t) -1</literal> instead. Note that
+                <function>poll()</function> 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:</para>
+
+                <programlisting>uint64_t t;
+int msec;
+sd_login_monitor_get_timeout(m, &amp;t);
+if (t == (uint64_t) -1)
+        msec = -1;
+else {
+        struct timespec ts;
+        uint64_t n;
+        clock_getttime(CLOCK_MONOTONIC, &amp;ts);
+        n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
+        msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
+}</programlisting>
+
+                <para>The code above does not do any error checking
+                for brevity's sake. The calculated <literal>msec</literal>
+                integer can be passed directly as
+                <function>poll()</function>'s timeout
+                parameter.</para>
         </refsect1>
 
         <refsect1>
                 <title>Return Value</title>
 
                 <para>On success
-                <function>sd_login_monitor_new()</function> and
-                <function>sd_login_monitor_flush()</function> return 0
-                or a positive integer. On success
+                <function>sd_login_monitor_new()</function>,
+                <function>sd_login_monitor_flush()</function> and
+                <function>sd_login_monitor_get_timeout()</function>
+                return 0 or a positive integer. On success
                 <function>sd_login_monitor_get_fd()</function> returns
                 a Unix file descriptor. On success
                 <function>sd_login_monitor_get_events()</function>
@@ -173,8 +218,9 @@
                 <para>The <function>sd_login_monitor_new()</function>,
                 <function>sd_login_monitor_unref()</function>,
                 <function>sd_login_monitor_flush()</function>,
-                <function>sd_login_monitor_get_fd()</function> and
-                <function>sd_login_monitor_get_events()</function>
+                <function>sd_login_monitor_get_fd()</function>,
+                <function>sd_login_monitor_get_events()</function> and
+                <function>sd_login_monitor_get_timeout()</function>
                 interfaces are available as shared library, which can
                 be compiled and linked to with the
                 <literal>libsystemd-login</literal>
@@ -189,7 +235,8 @@
                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
-                        <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+                        <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                 </para>
         </refsect1>