sd-journal: add an API to enumerate known field names of the journal

This adds two new calls to get the list of all journal fields names currently in use.

This is the low-level support to implement the feature requested in #2176 in a more optimized way.

1 files changed, 25 insertions, 19 deletions

diff --git a/man/sd_journal_query_unique.xml b/man/sd_journal_query_unique.xml
index ac0e5f633f..dbff55c105 100644
--- a/man/sd_journal_query_unique.xml
+++ b/man/sd_journal_query_unique.xml
@@ -128,6 +128,11 @@
     <para>Note that these functions currently are not influenced by
     matches set with <function>sd_journal_add_match()</function> but
     this might change in a later version of this software.</para>
+
+    <para>To enumerate all field names currently in use (and thus all suitable field parameters for
+    <function>sd_journal_query_unique()</function>), use the
+    <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    call.</para>
   </refsect1>
 
   <refsect1>
@@ -167,25 +172,25 @@
 #include &lt;systemd/sd-journal.h&gt;
 
 int main(int argc, char *argv[]) {
-  sd_journal *j;
-  const void *d;
-  size_t l;
-  int r;
-
-  r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
-  if (r &lt; 0) {
-    fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
-    return 1;
-  }
-  r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
-  if (r &lt; 0) {
-    fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
-    return 1;
-  }
-  SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
-    printf("%.*s\n", (int) l, (const char*) d);
-  sd_journal_close(j);
-  return 0;
+        sd_journal *j;
+        const void *d;
+        size_t l;
+        int r;
+
+        r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
+        if (r &lt; 0) {
+                fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
+                return 1;
+        }
+        r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
+        if (r &lt; 0) {
+                fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
+                return 1;
+        }
+        SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
+                printf("%.*s\n", (int) l, (const char*) d);
+        sd_journal_close(j);
+        return 0;
 }</programlisting>
 
   </refsect1>
@@ -198,6 +203,7 @@ int main(int argc, char *argv[]) {
       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     </para>