man/sd_journal_get_data.xml

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  23
  24 <refentry id="sd_journal_get_data">
  25
  26         <refentryinfo>
  27                 <title>sd_journal_get_data</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>sd_journal_get_data</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_journal_get_data</refname>
  47                 <refname>sd_journal_enumerate_data</refname>
  48                 <refname>sd_journal_restart_data</refname>
  49                 <refname>SD_JOURNAL_FOREACH_DATA</refname>
  50                 <refpurpose>Read data fields from the current journal entry</refpurpose>
  51         </refnamediv>
  52
  53         <refsynopsisdiv>
  54                 <funcsynopsis>
  55                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  56
  57                         <funcprototype>
  58                                 <funcdef>int <function>sd_journal_get_data</function></funcdef>
  59                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  60                                 <paramdef>const char* <parameter>field</parameter></paramdef>
  61                                 <paramdef>const void** <parameter>data</parameter></paramdef>
  62                                 <paramdef>size_t* <parameter>length</parameter></paramdef>
  63                         </funcprototype>
  64
  65                         <funcprototype>
  66                                 <funcdef>int <function>sd_journal_enumerate_data</function></funcdef>
  67                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  68                                 <paramdef>const void** <parameter>data</parameter></paramdef>
  69                                 <paramdef>size_t* <parameter>length</parameter></paramdef>
  70                         </funcprototype>
  71
  72                         <funcprototype>
  73                                 <funcdef>int <function>sd_journal_restart_data</function></funcdef>
  74                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  75                         </funcprototype>
  76
  77                         <funcprototype>
  78                                 <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef>
  79                                 <paramdef>sd_journal* <parameter>j</parameter></paramdef>
  80                                 <paramdef>const void* <parameter>data</parameter></paramdef>
  81                                 <paramdef>size_t <parameter>length</parameter></paramdef>
  82                         </funcprototype>
  83
  84                 </funcsynopsis>
  85         </refsynopsisdiv>
  86
  87         <refsect1>
  88                 <title>Description</title>
  89
  90                 <para><function>sd_journal_get_data()</function> gets
  91                 the data object associated with a specific field from
  92                 the current journal entry. It takes four arguments:
  93                 the journal context object, a string with the field
  94                 name to request, plus a pair of pointers to
  95                 pointer/size variables where the data object and its
  96                 size shall be stored in. The field name should be an
  97                 entry field name. Well-known field names are listed in
  98                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
  99                 returned data is in a read-only memory map and is only
 100                 valid until the next invocation of
 101                 <function>sd_journal_get_data()</function> or
 102                 <function>sd_journal_enumerate_data()</function>, or
 103                 the read pointer is altered. Note that the data
 104                 returned will be prefixed with the field name and
 105                 '='.</para>
 106
 107                 <para><function>sd_journal_enumerate_data()</function>
 108                 may be used to iterate through all fields of the
 109                 current entry. On each invocation the data for the
 110                 next field is returned. The order of these fields is
 111                 not defined. The data returned is in the same format
 112                 as with <function>sd_journal_get_data()</function> and
 113                 also follows the same life-time semantics.</para>
 114
 115                 <para><function>sd_journal_restart_data()</function>
 116                 resets the data enumeration index to the beginning of
 117                 the entry. The next invocation of
 118                 <function>sd_journal_enumerate_data()</function> will return the first
 119                 field of the entry again.</para>
 120
 121                 <para>Note that the
 122                 <function>SD_JOURNAL_FOREACH_DATA()</function> macro
 123                 may be used as a wrapper around
 124                 <function>sd_journal_restart_data()</function> and
 125                 <function>sd_journal_enumerate_data()</function>.</para>
 126
 127                 <para>Note that these functions will not work before
 128                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 129                 (or related call) has been called at least
 130                 once, in order to position the read pointer at a valid entry.</para>
 131         </refsect1>
 132
 133         <refsect1>
 134                 <title>Return Value</title>
 135
 136                 <para><function>sd_journal_get_data()</function>
 137                 returns 0 on success or a negative errno-style error
 138                 code. If the current entry does not include the
 139                 specified field -ENOENT is returned. If
 140                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 141                 has not been called at least once -EADDRNOTAVAIL is
 142                 returned. <function>sd_journal_enumerate_data()</function>
 143                 returns a positive integer if the next field has been
 144                 read, 0 when no more fields are known, or a negative
 145                 errno-style error
 146                 code. <function>sd_journal_restart_data()</function>
 147                 returns nothing.</para>
 148         </refsect1>
 149
 150         <refsect1>
 151                 <title>Notes</title>
 152
 153                 <para>The <function>sd_journal_get_data()</function>,
 154                 <function>sd_journal_enumerate_data()</function> and
 155                 <function>sd_journal_restart_data()</function>
 156                 interfaces are available as shared library, which can
 157                 be compiled and linked to with the
 158                 <literal>libsystemd-journal</literal>
 159                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 160                 file.</para>
 161         </refsect1>
 162
 163         <refsect1>
 164                 <title>Examples</title>
 165
 166                 <para>See
 167                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 168                 for a complete example how to use
 169                 <function>sd_journal_get_data()</function>.</para>
 170
 171                 <para>Use the
 172                 <function>SD_JOURNAL_FOREACH_DATA</function> macro to
 173                 iterate through all fields of the current journal
 174                 entry:</para>
 175
 176                 <programlisting>...
 177 int print_fields(sd_journal *j) {
 178         const void *data;
 179         size_t l;
 180         SD_JOURNAL_FOREACH_DATA(j, data, length)
 181                 printf("%.*s\n", (int) length, data);
 182 }
 183 ...</programlisting>
 184
 185         </refsect1>
 186
 187         <refsect1>
 188                 <title>See Also</title>
 189
 190                 <para>
 191                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 192                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 193                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 194                         <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 195                         <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 196                         <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 197                 </para>
 198         </refsect1>
 199
 200 </refentry>