-<!-- $Id: tools.xml,v 1.38 2004-10-02 13:41:46 adam Exp $ -->
+<!-- $Id: tools.xml,v 1.39 2004-11-16 17:08:11 heikki Exp $ -->
<chapter id="tools"><title>Supporting Tools</title>
<para>
</sect1>
+ <sect1 id="tools.log"><title>Log</title>
+ <para>
+ Yaz has evolved a fairly complex log system which should be useful both
+ for debugging &yaz; itself, debugging applications that use yaz, and for
+ production use of those applications.
+ </para>
+ <para>
+ The log functions are declared in <filename>log.h</filename> and
+ implemented in <filename>log.c</filename>. The key points of the interface
+ are:
+ </para>
+ <screen>
+ void yaz_log(int level, const char *fmt, ...)
+
+ void yaz_log_init(int level, const char *prefix, const char *name);
+ void yaz_log_init_file(const char *fname);
+ void yaz_log_init_level(int level);
+ void yaz_log_init_prefix(const char *prefix);
+ void yaz_log_time_format(const char *fmt);
+ void yaz_log_init_max_size(int mx);
+
+ int yaz_log_mask_str(const char *str);
+ int yaz_log_module_level(const char *name);
+ </screen>
+
+ <para>
+ The reason for the whole log module is the <function>yaz_log</function>
+ function. It takes a bitmask indicating the log levels, a
+ <literal>printf</literal>-like format string, and a variable number of
+ arguments to log.
+ </para>
+
+ <para>
+ The <literal>log level</literal> is a bit mask, that says on which level(s)
+ the log entry should be made, and optionally set some behaviour of the
+ logging. In the most simple cases, it can be one of <literal>LOG_FATAL,
+ LOG_DEBUG, LOG_WARN, LOG_LOG</literal>. Those can be combined with bits
+ that modify the way the log entry is written:<literal>LOG_ERRNO, LOG_NOTIME,
+ LOG_FLUSH</literal>. Most of the rest of the bits are deprecated, and
+ should not be used.
+ </para>
+
+ <para>
+ Applications that use yaz, should not use the LOG_LOG for ordinary
+ messages, but should make use of the dynamic loglevel system. This consists
+ of two parts, defining the loglevel and checking it.
+ </para>
+
+ <para>
+ To define the log levels, the (main) program should pass a string to
+ <function>yaz_log_mask_str</function> to define which log levels are to be
+ logged. This string should be a comma-separated list of log level names,
+ and can contain both hard-coded names and dynamic ones. The log level
+ calculation starts with <literal>LOG_DEFAULT_LEVEL</literal> and adds a bit
+ for each word it meets. If the string <literal>'none'</literal> is found,
+ the bits are cleared. Typically this string comes from the command-line,
+ often identified by <literal>-v</literal>. The
+ <function>yaz_log_mask_str</function> returns a log level that should be
+ passed to <function>yaz_log_init_level</function> for it to take effect.
+ </para>
+
+ <para>
+ Each module should check what log bits it should be used, by calling
+ <function>yaz_log_module_level</function> with a suitable name for the
+ module. The name is cleared from a preceding path and an extension, if any,
+ so it is quite possible to use <literal>__FILE__</literal> for it. If the
+ name has been passed to <function>yaz_log_mask_str</function>, the routine
+ returns a non-zero bitmask, which should then be used in consequent calls
+ to yaz_log. (It can also be tested, so as to avoid unnecessary calls to
+ yaz_log, in time-critical places, or when the log entry would take time
+ to construct.)
+ </para>
+
+ <para>
+ By default the log is written to stderr, but this can be changed by a call
+ to <function>yaz_log_init_file</function> or
+ <function>yaz_log_init</function>. If the log is directed to a file, the
+ file size is checked at every write, and if it exceeds the limit given in
+ <function>yaz_log_init_max_size</function>, the log is rotated. The
+ rotation keeps one old version (with a <literal>.1</literal> appended to
+ the name). The size defaults to 1GB. Setting it to zero will disable the
+ rotation feature.
+ </para>
+
+ <para>
+ The log entries start with a time stamp. This can be omitted by setting the
+ <literal>LOG_NOTIME</literal> bit in the loglevel. This way automatic tests
+ can be hoped to produce identical log files, that are easy to diff. The
+ format of the time stamp can be set with
+ <function>yaz_log_time_format</function>, which takes a format string just
+ like <function>strftime</function>.
+ </para>
+
+ <para>
+ Next in a log line comes the prefix, often the name of the program. Then
+ comes one or more logbits in square brackets, depending on the logging
+ level set by <function>yaz_log_init_level</function> and the loglevel
+ passed to <function>yaz_log_init_level</function>. Finally comes all format
+ string and additional values passed to <function>yaz_log</function>
+ </para>
+
+ <para>
+ The log level <literal>LOG_LOGLVL</literal>, enabled by the string
+ <literal>loglevel</literal>, will log all the log-level affecting
+ operations. This can come in handy if you need to know what other log
+ levels would be useful. Grep the logfile for <literal>[loglevel]</literal>.
+ </para>
+
+ <para>
+ The log system is almost independent of the rest of &yaz;, the only
+ important dependence is of <filename>nmem</filename>, and that only for
+ using the semaphore definition there.
+ </para>
+
+ <para>
+ The dynamic log levels and log rotation were introduced in &yaz; 2.0.28.
+ </para>
+
+ </sect1>
+
<sect1 id="tools.marc"><title>MARC</title>
<para>
projects / yaz-moved-to-github.git / blobdiff