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.
The log functions are declared in header
and implemented in
Due to name clash with syslog and some math utilities the logging
interface has been modified as of YAZ 2.0.29. The obsolete interface
is still available in header file
The key points of the interface are:
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);
The reason for the whole log module is the
function. It takes a bitmask indicating the log levels, a
printf-like format string, and a variable number of
arguments to log.
log level 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
YLOG_DEBUG, YLOG_WARN, YLOG_LOG. Those can be combined with bits
that modify the way the log entry is written:
Most of the rest of the bits are deprecated, and should not be used. Use
the dynamic log levels instead.
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.
To define the log levels, the (main) program should pass a string to
yaz_log_mask_str 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
YLOG_DEFAULT_LEVEL and adds a bit
for each word it meets, unless the word starts with a '-', in which case it
clears the bit. If the string
'none' is found,
all bits are cleared. Typically this string comes from the command-line,
often identified by
yaz_log_mask_str returns a log level that should be
yaz_log_init_level for it to take effect.
Each module should check what log bits should be used, by calling
yaz_log_module_level with a suitable name for the
module. The name is cleared of a preceding path and an extension, if any,
so it is quite possible to use
__FILE__ for it. If the
name has been passed to
yaz_log_mask_str, 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
Yaz uses the following dynamic log levels:
server, session, request, requestdetail for the server
zoom for the zoom client API.
ztest for the simple test server.
malloc, nmem, odr, eventl for internal
debugging of yaz itself.
Of course, any program using yaz is welcome to define as many new
ones as it needs.
By default the log is written to stderr, but this can be changed by a call
yaz_log_init. If the log is directed to a file, the
file size is checked at every write, and if it exceeds the limit given in
yaz_log_init_max_size, the log is rotated. The
rotation keeps one old version (with a
.1 appended to
the name). The size defaults to 1GB. Setting it to zero will disable the
A typical yaz-log looks like this 13:23:14-23/11 yaz-ztest(1) [session] Starting session from tcp:127.0.0.1 (pid=30968) 13:23:14-23/11 yaz-ztest(1) [request] Init from 'YAZ' (81) (ver 2.0.28) OK 13:23:17-23/11 yaz-ztest(1) [request] Search Z: @attrset Bib-1 foo OK:7 hits 13:23:22-23/11 yaz-ztest(1) [request] Present:  2+2 OK 2 records returned 13:24:13-23/11 yaz-ztest(1) [request] Close OK
The log entries start with a time stamp. This can be omitted by setting the
YLOG_NOTIME 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
yaz_log_time_format, which takes a format string just
Next in a log line comes the prefix, often the name of the program. For
yaz-based servers, it can also contain the session number. Then
comes one or more logbits in square brackets, depending on the logging
level set by
yaz_log_init_level and the loglevel
yaz_log_init_level. Finally comes the format
string and additional values passed to
The log level
YLOG_LOGLVL, enabled by the string
loglevel, 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
The log system is almost independent of the rest of YAZ, the only
important dependence is of
nmem, and that only for
using the semaphore definition there.
The dynamic log levels and log rotation were introduced in YAZ 2.0.28. At
the same time, the log bit names were changed from
to avoid collision with