| <?xml version='1.0'?> <!--*-nxml-*--> |
| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
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| Copyright 2012 Lennart Poettering |
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| |
| <refentry id="sd_journal_get_data"> |
| |
| <refentryinfo> |
| <title>sd_journal_get_data</title> |
| <productname>systemd</productname> |
| |
| <authorgroup> |
| <author> |
| <contrib>Developer</contrib> |
| <firstname>Lennart</firstname> |
| <surname>Poettering</surname> |
| <email>lennart@poettering.net</email> |
| </author> |
| </authorgroup> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>sd_journal_get_data</refentrytitle> |
| <manvolnum>3</manvolnum> |
| </refmeta> |
| |
| <refnamediv> |
| <refname>sd_journal_get_data</refname> |
| <refname>sd_journal_enumerate_data</refname> |
| <refname>sd_journal_restart_data</refname> |
| <refname>SD_JOURNAL_FOREACH_DATA</refname> |
| <refname>sd_journal_set_data_threshold</refname> |
| <refname>sd_journal_get_data_threshold</refname> |
| <refpurpose>Read data fields from the current journal entry</refpurpose> |
| </refnamediv> |
| |
| <refsynopsisdiv> |
| <funcsynopsis> |
| <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> |
| |
| <funcprototype> |
| <funcdef>int <function>sd_journal_get_data</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| <paramdef>const char *<parameter>field</parameter></paramdef> |
| <paramdef>const void **<parameter>data</parameter></paramdef> |
| <paramdef>size_t *<parameter>length</parameter></paramdef> |
| </funcprototype> |
| |
| <funcprototype> |
| <funcdef>int <function>sd_journal_enumerate_data</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| <paramdef>const void **<parameter>data</parameter></paramdef> |
| <paramdef>size_t *<parameter>length</parameter></paramdef> |
| </funcprototype> |
| |
| <funcprototype> |
| <funcdef>void <function>sd_journal_restart_data</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| </funcprototype> |
| |
| <funcprototype> |
| <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| <paramdef>const void *<parameter>data</parameter></paramdef> |
| <paramdef>size_t <parameter>length</parameter></paramdef> |
| </funcprototype> |
| |
| <funcprototype> |
| <funcdef>int <function>sd_journal_set_data_threshold</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| <paramdef>size_t <parameter>sz</parameter></paramdef> |
| </funcprototype> |
| |
| <funcprototype> |
| <funcdef>int <function>sd_journal_get_data_threshold</function></funcdef> |
| <paramdef>sd_journal *<parameter>j</parameter></paramdef> |
| <paramdef>size_t *<parameter>sz</parameter></paramdef> |
| </funcprototype> |
| </funcsynopsis> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para><function>sd_journal_get_data()</function> gets |
| the data object associated with a specific field from |
| the current journal entry. It takes four arguments: |
| the journal context object, a string with the field |
| name to request, plus a pair of pointers to |
| pointer/size variables where the data object and its |
| size shall be stored in. The field name should be an |
| entry field name. Well-known field names are listed in |
| <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The |
| returned data is in a read-only memory map and is only |
| valid until the next invocation of |
| <function>sd_journal_get_data()</function> or |
| <function>sd_journal_enumerate_data()</function>, or |
| the read pointer is altered. Note that the data |
| returned will be prefixed with the field name and |
| '='. Also note that by default data fields larger than |
| 64K might get truncated to 64K. This threshold may be |
| changed and turned off with |
| <function>sd_journal_set_data_threshold()</function> (see |
| below).</para> |
| |
| <para><function>sd_journal_enumerate_data()</function> |
| may be used to iterate through all fields of the |
| current entry. On each invocation the data for the |
| next field is returned. The order of these fields is |
| not defined. The data returned is in the same format |
| as with <function>sd_journal_get_data()</function> and |
| also follows the same life-time semantics.</para> |
| |
| <para><function>sd_journal_restart_data()</function> |
| resets the data enumeration index to the beginning of |
| the entry. The next invocation of |
| <function>sd_journal_enumerate_data()</function> will return the first |
| field of the entry again.</para> |
| |
| <para>Note that the |
| <function>SD_JOURNAL_FOREACH_DATA()</function> macro |
| may be used as a handy wrapper around |
| <function>sd_journal_restart_data()</function> and |
| <function>sd_journal_enumerate_data()</function>.</para> |
| |
| <para>Note that these functions will not work before |
| <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| (or related call) has been called at least |
| once, in order to position the read pointer at a valid entry.</para> |
| |
| <para><function>sd_journal_set_data_threshold()</function> |
| may be used to change the data field size threshold |
| for data returned by |
| <function>sd_journal_get_data()</function>, |
| <function>sd_journal_enumerate_data()</function> and |
| <function>sd_journal_enumerate_unique()</function>. This |
| threshold is a hint only: it indicates that the client |
| program is interested only in the initial parts of the |
| data fields, up to the threshold in size -- but the |
| library might still return larger data objects. That |
| means applications should not rely exclusively on this |
| setting to limit the size of the data fields returned, |
| but need to apply a explicit size limit on the |
| returned data as well. This threshold defaults to 64K |
| by default. To retrieve the complete data fields this |
| threshold should be turned off by setting it to 0, so |
| that the library always returns the complete data |
| objects. It is recommended to set this threshold as |
| low as possible since this relieves the library from |
| having to decompress large compressed data objects in |
| full.</para> |
| |
| <para><function>sd_journal_get_data_threshold()</function> |
| returns the currently configured data field size |
| threshold.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Return Value</title> |
| |
| <para><function>sd_journal_get_data()</function> |
| returns 0 on success or a negative errno-style error |
| code. If the current entry does not include the |
| specified field, -ENOENT is returned. If |
| <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| has not been called at least once, -EADDRNOTAVAIL is |
| returned. <function>sd_journal_enumerate_data()</function> |
| returns a positive integer if the next field has been |
| read, 0 when no more fields are known, or a negative |
| errno-style error |
| code. <function>sd_journal_restart_data()</function> |
| returns |
| nothing. <function>sd_journal_set_data_threshold()</function> |
| and <function>sd_journal_get_threshold()</function> |
| return 0 on success or a negative errno-style error |
| code.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Notes</title> |
| |
| <para>The <function>sd_journal_get_data()</function>, |
| <function>sd_journal_enumerate_data()</function>, |
| <function>sd_journal_restart_data()</function>, |
| <function>sd_journal_set_data_threshold()</function> |
| and |
| <function>sd_journal_get_data_threshold()</function> |
| interfaces are available as a shared library, which can |
| be compiled and linked to with the |
| <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| file.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Examples</title> |
| |
| <para>See |
| <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| for a complete example how to use |
| <function>sd_journal_get_data()</function>.</para> |
| |
| <para>Use the |
| <function>SD_JOURNAL_FOREACH_DATA</function> macro to |
| iterate through all fields of the current journal |
| entry:</para> |
| |
| <programlisting>... |
| int print_fields(sd_journal *j) { |
| const void *data; |
| size_t length; |
| SD_JOURNAL_FOREACH_DATA(j, data, length) |
| printf("%.*s\n", (int) length, data); |
| } |
| ...</programlisting> |
| |
| </refsect1> |
| |
| <refsect1> |
| <title>See Also</title> |
| |
| <para> |
| <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <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_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |