man/SD_JOURNAL_FOREACH_UNIQUE.html

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  22   <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 219</span><hr><div class="refentry"><a name="sd_journal_query_unique"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE — Read unique data fields from the journal</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;systemd/sd-journal.h&gt;</pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_query_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">field</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_enumerate_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void **<var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">length</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <b class="fsfunc">sd_journal_restart_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef"><b class="fsfunc">SD_JOURNAL_FOREACH_UNIQUE</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void *<var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm140488052010080"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_journal_query_unique()</code> queries the
  23     journal for all unique values the specified field can take. It
  24     takes two arguments: the journal to query and the field name to
  25     look for. Well-known field names are listed on
  26     <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>.
  27     Field names must be specified without a trailing '='. After this
  28     function has been executed successfully the field values may be
  29     queried using <code class="function">sd_journal_enumerate_unique()</code>.
  30     Invoking this call a second time will change the field name being
  31     queried and reset the enumeration index to the first field value
  32     that matches.</p><p><code class="function">sd_journal_enumerate_unique()</code> may be
  33     used to iterate through all data fields which match the previously
  34     selected field name as set with
  35     <code class="function">sd_journal_query_unique()</code>. On each invocation
  36     the next field data matching the field name is returned. The order
  37     of the returned data fields is not defined. It takes three
  38     arguments: the journal context object, plus a pair of pointers to
  39     pointer/size variables where the data object and its size shall be
  40     stored in. The returned data is in a read-only memory map and is
  41     only valid until the next invocation of
  42     <code class="function">sd_journal_enumerate_unique()</code>. Note that the
  43     data returned will be prefixed with the field name and '='. Note
  44     that this call is subject to the data field size threshold as
  45     controlled by
  46     <code class="function">sd_journal_set_data_threshold()</code>.</p><p><code class="function">sd_journal_restart_unique()</code> resets the
  47     data enumeration index to the beginning of the list. The next
  48     invocation of <code class="function">sd_journal_enumerate_unique()</code>
  49     will return the first field data matching the field name
  50     again.</p><p>Note that the
  51     <code class="function">SD_JOURNAL_FOREACH_UNIQUE()</code> macro may be used
  52     as a handy wrapper around
  53     <code class="function">sd_journal_restart_unique()</code> and
  54     <code class="function">sd_journal_enumerate_unique()</code>.</p><p>Note that these functions currently are not influenced by
  55     matches set with <code class="function">sd_journal_add_match()</code> but
  56     this might change in a later version of this software.</p></div><div class="refsect1"><a name="idm140488051997008"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p><code class="function">sd_journal_query_unique()</code> returns 0 on
  57     success or a negative errno-style error code.
  58     <code class="function">sd_journal_enumerate_unique()</code> returns a
  59     positive integer if the next field data has been read, 0 when no
  60     more fields are known, or a negative errno-style error code.
  61     <code class="function">sd_journal_restart_unique()</code> returns
  62     nothing.</p></div><div class="refsect1"><a name="idm140488051993648"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p>The <code class="function">sd_journal_query_unique()</code>,
  63     <code class="function">sd_journal_enumerate_unique()</code> and
  64     <code class="function">sd_journal_restart_unique()</code> interfaces are
  65     available as a shared library, which can be compiled and linked to
  66     with the
  67     <code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
  68     file.</p></div><div class="refsect1"><a name="idm140488051981152"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>Use the <code class="function">SD_JOURNAL_FOREACH_UNIQUE</code> macro
  69     to iterate through all values a field of the journal can take. The
  70     following example lists all unit names referenced in the
  71     journal:</p><pre class="programlisting">#include &lt;stdio.h&gt;
  72 #include &lt;string.h&gt;
  73 #include &lt;systemd/sd-journal.h&gt;
  74
  75 int main(int argc, char *argv[]) {
  76   sd_journal *j;
  77   const void *d;
  78   size_t l;
  79   int r;
  80
  81   r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
  82   if (r &lt; 0) {
  83     fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
  84     return 1;
  85   }
  86   r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
  87   if (r &lt; 0) {
  88     fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
  89     return 1;
  90   }
  91   SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
  92     printf("%.*s\n", (int) l, (const char*) d);
  93   sd_journal_close(j);
  94   return 0;
  95 }</pre></div><div class="refsect1"><a name="idm140488051976848"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
  96       <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
  97       <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>,
  98       <a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
  99       <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
 100       <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>,
 101       <a href="sd_journal_add_match.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_add_match</span>(3)</span></a>
 102     </p></div></div></body></html>