man/sd_journal_enumerate_unique.html

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  22   <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 208</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="idm274683751280"></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>
  23                 queries the journal for all unique values the
  24                 specified field can take. It takes two arguments: the
  25                 journal to query and the field name to look
  26                 for. Well-known field names are listed on
  27                 <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>. Field
  28                 names must be specified without a trailing '='. After
  29                 this function has been executed successfully the field
  30                 values may be queried using
  31                 <code class="function">sd_journal_enumerate_unique()</code>. Invoking
  32                 this call a second time will change the field name
  33                 being queried and reset the enumeration index to the
  34                 first field value that matches.</p><p><code class="function">sd_journal_enumerate_unique()</code>
  35                 may be used to iterate through all data fields which
  36                 match the previously selected field name as set with
  37                 <code class="function">sd_journal_query_unique()</code>. On
  38                 each invocation the next field data matching the field
  39                 name is returned. The order of the returned data
  40                 fields is not defined. It takes three arguments: the
  41                 journal context object, plus a pair of pointers to
  42                 pointer/size variables where the data object and its
  43                 size shall be stored in. The returned data is in a
  44                 read-only memory map and is only valid until the next
  45                 invocation of
  46                 <code class="function">sd_journal_enumerate_unique()</code>. Note
  47                 that the data returned will be prefixed with the field
  48                 name and '='. Note that this call is subject to the
  49                 data field size threshold as controlled by
  50                 <code class="function">sd_journal_set_data_threshold()</code>.</p><p><code class="function">sd_journal_restart_unique()</code>
  51                 resets the data enumeration index to the beginning of
  52                 the list. The next invocation of
  53                 <code class="function">sd_journal_enumerate_unique()</code>
  54                 will return the first field data matching the field
  55                 name again.</p><p>Note that the
  56                 <code class="function">SD_JOURNAL_FOREACH_UNIQUE()</code> macro
  57                 may be used as a handy wrapper around
  58                 <code class="function">sd_journal_restart_unique()</code> and
  59                 <code class="function">sd_journal_enumerate_unique()</code>.</p><p>Note that these functions currently are not
  60                 influenced by matches set with
  61                 <code class="function">sd_journal_add_match()</code> but this
  62                 might change in a later version of this
  63                 software.</p></div><div class="refsect1"><a name="idm274683737440"></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>
  64                 returns 0 on success or a negative errno-style error
  65                 code. <code class="function">sd_journal_enumerate_unique()</code>
  66                 returns a positive integer if the next field data has
  67                 been read, 0 when no more fields are known, or a
  68                 negative errno-style error
  69                 code. <code class="function">sd_journal_restart_unique()</code>
  70                 returns nothing.</p></div><div class="refsect1"><a name="idm274683726464"></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>,
  71                 <code class="function">sd_journal_enumerate_unique()</code> and
  72                 <code class="function">sd_journal_restart_unique()</code>
  73                 interfaces are available as shared library, which can
  74                 be compiled and linked to with the
  75                 <code class="constant">libsystemd-journal</code> <a href="pkg-config.html"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
  76                 file.</p></div><div class="refsect1"><a name="idm274683721584"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>Use the
  77                 <code class="function">SD_JOURNAL_FOREACH_UNIQUE</code> macro
  78                 to iterate through all values a field of the journal
  79                 can take. The following example lists all unit names
  80                 referenced in the journal:</p><pre class="programlisting">#include &lt;stdio.h&gt;
  81 #include &lt;string.h&gt;
  82 #include &lt;systemd/sd-journal.h&gt;
  83
  84 int main(int argc, char *argv[]) {
  85         sd_journal *j;
  86         const void *d;
  87         size_t l;
  88         int r;
  89
  90         r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
  91         if (r &lt; 0) {
  92                 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
  93                 return 1;
  94         }
  95         r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
  96         if (r &lt; 0) {
  97                 fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
  98                 return 1;
  99         }
 100         SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
 101                 printf("%.*s\n", (int) l, (const char*) d);
 102         sd_journal_close(j);
 103         return 0;
 104 }</pre></div><div class="refsect1"><a name="idm274683716976"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
 105                         <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
 106                         <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>,
 107                         <a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
 108                         <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
 109                         <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>,
 110                         <a href="sd_journal_add_match.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_add_match</span>(3)</span></a>
 111                 </p></div></div></body></html>