man: document signal unsafeness of journal functions

Fixes #7912.

diff --git a/man/sd_journal_get_fd.xml b/man/sd_journal_get_fd.xml
index b162b2bf114ca0020a003741c50aa99f740b0065..24ececd9cbb52a5f6568d75a6d373ddc6fd5f69e 100644 (file)
--- a/man/sd_journal_get_fd.xml
+++ b/man/sd_journal_get_fd.xml
@@ -230,6 +230,20 @@ else {
     journal.</para>
   </refsect1>
 
+  <refsect1>
+    <title>Signal safety</title>
+
+    <para>In general, <function>sd_journal_get_fd()</function>,
+    <function>sd_journal_get_events()</function>, and <function>sd_journal_get_timeout()</function>
+    are <emphasis>not</emphasis> "async signal safe" in the meaning of
+    <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+    Nevertheless, only the first call to any of those three functions performs unsafe operations, so
+    subsequent calls <emphasis>are</emphasis> safe.</para>
+
+    <para><function>sd_journal_process()</function> and <function>sd_journal_wait()</function> are not
+    safe. <function>sd_journal_reliable_fd()</function> is safe.</para>
+  </refsect1>
+
   <refsect1>
     <title>Notes</title>