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f47781d8 | 22 | <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 218</span><hr><div class="refentry"><a name="sd_journal_get_data"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_get_data, sd_journal_enumerate_data, sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA, sd_journal_set_data_threshold, sd_journal_get_data_threshold — Read data fields from the current journal entry</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-journal.h></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_get_data</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">field</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">int <b class="fsfunc">sd_journal_enumerate_data</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_data</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_DATA</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">int <b class="fsfunc">sd_journal_set_data_threshold</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">sz</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_get_data_threshold</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">sz</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm140399443665936"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_journal_get_data()</code> gets |
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23 | the data object associated with a specific field from |
24 | the current journal entry. It takes four arguments: | |
25 | the journal context object, a string with the field | |
26 | name to request, plus a pair of pointers to | |
27 | pointer/size variables where the data object and its | |
28 | size shall be stored in. The field name should be an | |
29 | entry field name. Well-known field names are listed in | |
30 | <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>. The | |
31 | returned data is in a read-only memory map and is only | |
32 | valid until the next invocation of | |
33 | <code class="function">sd_journal_get_data()</code> or | |
34 | <code class="function">sd_journal_enumerate_data()</code>, or | |
35 | the read pointer is altered. Note that the data | |
36 | returned will be prefixed with the field name and | |
37 | '='. Also note that by default data fields larger than | |
38 | 64K might get truncated to 64K. This threshold may be | |
39 | changed and turned off with | |
40 | <code class="function">sd_journal_set_data_threshold()</code> (see | |
41 | below).</p><p><code class="function">sd_journal_enumerate_data()</code> | |
42 | may be used to iterate through all fields of the | |
43 | current entry. On each invocation the data for the | |
44 | next field is returned. The order of these fields is | |
45 | not defined. The data returned is in the same format | |
46 | as with <code class="function">sd_journal_get_data()</code> and | |
47 | also follows the same life-time semantics.</p><p><code class="function">sd_journal_restart_data()</code> | |
48 | resets the data enumeration index to the beginning of | |
49 | the entry. The next invocation of | |
50 | <code class="function">sd_journal_enumerate_data()</code> will return the first | |
51 | field of the entry again.</p><p>Note that the | |
52 | <code class="function">SD_JOURNAL_FOREACH_DATA()</code> macro | |
53 | may be used as a handy wrapper around | |
54 | <code class="function">sd_journal_restart_data()</code> and | |
55 | <code class="function">sd_journal_enumerate_data()</code>.</p><p>Note that these functions will not work before | |
56 | <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a> | |
57 | (or related call) has been called at least | |
58 | once, in order to position the read pointer at a valid entry.</p><p><code class="function">sd_journal_set_data_threshold()</code> | |
59 | may be used to change the data field size threshold | |
60 | for data returned by | |
61 | <code class="function">sd_journal_get_data()</code>, | |
62 | <code class="function">sd_journal_enumerate_data()</code> and | |
63 | <code class="function">sd_journal_enumerate_unique()</code>. This | |
64 | threshold is a hint only: it indicates that the client | |
65 | program is interested only in the initial parts of the | |
66 | data fields, up to the threshold in size -- but the | |
67 | library might still return larger data objects. That | |
68 | means applications should not rely exclusively on this | |
69 | setting to limit the size of the data fields returned, | |
70 | but need to apply a explicit size limit on the | |
71 | returned data as well. This threshold defaults to 64K | |
72 | by default. To retrieve the complete data fields this | |
73 | threshold should be turned off by setting it to 0, so | |
74 | that the library always returns the complete data | |
75 | objects. It is recommended to set this threshold as | |
76 | low as possible since this relieves the library from | |
77 | having to decompress large compressed data objects in | |
78 | full.</p><p><code class="function">sd_journal_get_data_threshold()</code> | |
79 | returns the currently configured data field size | |
f47781d8 | 80 | threshold.</p></div><div class="refsect1"><a name="idm140399443639760"></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_get_data()</code> |
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81 | returns 0 on success or a negative errno-style error |
82 | code. If the current entry does not include the | |
14228c0d | 83 | specified field, -ENOENT is returned. If |
663996b3 | 84 | <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a> |
14228c0d | 85 | has not been called at least once, -EADDRNOTAVAIL is |
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86 | returned. <code class="function">sd_journal_enumerate_data()</code> |
87 | returns a positive integer if the next field has been | |
88 | read, 0 when no more fields are known, or a negative | |
89 | errno-style error | |
90 | code. <code class="function">sd_journal_restart_data()</code> | |
91 | returns | |
92 | nothing. <code class="function">sd_journal_set_data_threshold()</code> | |
93 | and <code class="function">sd_journal_get_threshold()</code> | |
94 | return 0 on success or a negative errno-style error | |
f47781d8 | 95 | code.</p></div><div class="refsect1"><a name="idm140399443633712"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p>The <code class="function">sd_journal_get_data()</code>, |
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96 | <code class="function">sd_journal_enumerate_data()</code>, |
97 | <code class="function">sd_journal_restart_data()</code>, | |
98 | <code class="function">sd_journal_set_data_threshold()</code> | |
99 | and | |
100 | <code class="function">sd_journal_get_data_threshold()</code> | |
60f067b4 | 101 | interfaces are available as a shared library, which can |
663996b3 | 102 | be compiled and linked to with the |
5eef597e | 103 | <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> |
f47781d8 | 104 | file.</p></div><div class="refsect1"><a name="idm140399438662352"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>See |
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105 | <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a> |
106 | for a complete example how to use | |
107 | <code class="function">sd_journal_get_data()</code>.</p><p>Use the | |
108 | <code class="function">SD_JOURNAL_FOREACH_DATA</code> macro to | |
109 | iterate through all fields of the current journal | |
110 | entry:</p><pre class="programlisting">... | |
111 | int print_fields(sd_journal *j) { | |
112 | const void *data; | |
e842803a | 113 | size_t length; |
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114 | SD_JOURNAL_FOREACH_DATA(j, data, length) |
115 | printf("%.*s\n", (int) length, data); | |
116 | } | |
f47781d8 | 117 | ...</pre></div><div class="refsect1"><a name="idm140399438657856"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p> |
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118 | <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>, |
119 | <a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>, | |
120 | <a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>, | |
121 | <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>, | |
122 | <a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>, | |
123 | <a href="sd_journal_get_realtime_usec.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_realtime_usec</span>(3)</span></a>, | |
124 | <a href="sd_journal_query_unique.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_query_unique</span>(3)</span></a> | |
125 | </p></div></div></body></html> |