diff options
Diffstat (limited to 'docs/devel/debug.xml')
| -rw-r--r-- | docs/devel/debug.xml | 321 |
1 files changed, 321 insertions, 0 deletions
diff --git a/docs/devel/debug.xml b/docs/devel/debug.xml new file mode 100644 index 0000000000..7e81cc825d --- /dev/null +++ b/docs/devel/debug.xml @@ -0,0 +1,321 @@ +<chapter id="debug"> +<chapterinfo> + <author> + <firstname>Chris</firstname><surname>Hertel</surname> + </author> + <pubdate>July 1998</pubdate> +</chapterinfo> + +<title>The samba DEBUG system</title> + +<sect1> +<title>New Output Syntax</title> + +<para> + The syntax of a debugging log file is represented as: +</para> + +<para><programlisting> + >debugfile< :== { >debugmsg< } + + >debugmsg< :== >debughdr< '\n' >debugtext< + + >debughdr< :== '[' TIME ',' LEVEL ']' FILE ':' [FUNCTION] '(' LINE ')' + + >debugtext< :== { >debugline< } + + >debugline< :== TEXT '\n' +</programlisting></para> + +<para> +TEXT is a string of characters excluding the newline character. +</para> + +<para> +LEVEL is the DEBUG level of the message (an integer in the range + 0..10). +</para> + +<para> +TIME is a timestamp. +</para> + +<para> +FILE is the name of the file from which the debug message was +generated. +</para> + +<para> +FUNCTION is the function from which the debug message was generated. +</para> + +<para> +LINE is the line number of the debug statement that generated the +message. +</para> + +<para>Basically, what that all means is:</para> +<orderedlist> +<listitem><para> +A debugging log file is made up of debug messages. +</para></listitem> +<listitem><para> +Each debug message is made up of a header and text. The header is +separated from the text by a newline. +</para></listitem> +<listitem><para> +The header begins with the timestamp and debug level of the +message enclosed in brackets. The filename, function, and line +number at which the message was generated follow. The filename is +terminated by a colon, and the function name is terminated by the +parenthesis which contain the line number. Depending upon the +compiler, the function name may be missing (it is generated by the +__FUNCTION__ macro, which is not universally implemented, dangit). +</para></listitem> +<listitem><para> +The message text is made up of zero or more lines, each terminated +by a newline. +</para></listitem> +</orderedlist> + +<para>Here's some example output:</para> + +<para><programlisting> + [1998/08/03 12:55:25, 1] nmbd.c:(659) + Netbios nameserver version 1.9.19-prealpha started. + Copyright Andrew Tridgell 1994-1997 + [1998/08/03 12:55:25, 3] loadparm.c:(763) + Initializing global parameters +</programlisting></para> + +<para> +Note that in the above example the function names are not listed on +the header line. That's because the example above was generated on an +SGI Indy, and the SGI compiler doesn't support the __FUNCTION__ macro. +</para> + +</sect1> + +<sect1> +<title>The DEBUG() Macro</title> + +<para> +Use of the DEBUG() macro is unchanged. DEBUG() takes two parameters. +The first is the message level, the second is the body of a function +call to the Debug1() function. +</para> + +<para>That's confusing.</para> + +<para>Here's an example which may help a bit. If you would write</para> + +<para><programlisting> +printf( "This is a %s message.\n", "debug" ); +</programlisting></para> + +<para> +to send the output to stdout, then you would write +</para> + +<para><programlisting> +DEBUG( 0, ( "This is a %s message.\n", "debug" ) ); +</programlisting></para> + +<para> +to send the output to the debug file. All of the normal printf() +formatting escapes work. +</para> + +<para> +Note that in the above example the DEBUG message level is set to 0. +Messages at level 0 always print. Basically, if the message level is +less than or equal to the global value DEBUGLEVEL, then the DEBUG +statement is processed. +</para> + +<para> +The output of the above example would be something like: +</para> + +<para><programlisting> + [1998/07/30 16:00:51, 0] file.c:function(128) + This is a debug message. +</programlisting></para> + +<para> +Each call to DEBUG() creates a new header *unless* the output produced +by the previous call to DEBUG() did not end with a '\n'. Output to the +debug file is passed through a formatting buffer which is flushed +every time a newline is encountered. If the buffer is not empty when +DEBUG() is called, the new input is simply appended. +</para> + +<para> +...but that's really just a Kludge. It was put in place because +DEBUG() has been used to write partial lines. Here's a simple (dumb) +example of the kind of thing I'm talking about: +</para> + +<para><programlisting> + DEBUG( 0, ("The test returned " ) ); + if( test() ) + DEBUG(0, ("True") ); + else + DEBUG(0, ("False") ); + DEBUG(0, (".\n") ); +</programlisting></para> + +<para> +Without the format buffer, the output (assuming test() returned true) +would look like this: +</para> + +<para><programlisting> + [1998/07/30 16:00:51, 0] file.c:function(256) + The test returned + [1998/07/30 16:00:51, 0] file.c:function(258) + True + [1998/07/30 16:00:51, 0] file.c:function(261) + . +</programlisting></para> + +<para>Which isn't much use. The format buffer kludge fixes this problem. +</para> + +</sect1> + +<sect1> +<title>The DEBUGADD() Macro</title> + +<para> +In addition to the kludgey solution to the broken line problem +described above, there is a clean solution. The DEBUGADD() macro never +generates a header. It will append new text to the current debug +message even if the format buffer is empty. The syntax of the +DEBUGADD() macro is the same as that of the DEBUG() macro. +</para> + +<para><programlisting> + DEBUG( 0, ("This is the first line.\n" ) ); + DEBUGADD( 0, ("This is the second line.\nThis is the third line.\n" ) ); +</programlisting></para> + +<para>Produces</para> + +<para><programlisting> + [1998/07/30 16:00:51, 0] file.c:function(512) + This is the first line. + This is the second line. + This is the third line. +</programlisting></para> + +</sect1> + +<sect1> +<title>The DEBUGLVL() Macro</title> + +<para> +One of the problems with the DEBUG() macro was that DEBUG() lines +tended to get a bit long. Consider this example from +nmbd_sendannounce.c: +</para> + +<para><programlisting> + DEBUG(3,("send_local_master_announcement: type %x for name %s on subnet %s for workgroup %s\n", + type, global_myname, subrec->subnet_name, work->work_group)); +</programlisting></para> + +<para> +One solution to this is to break it down using DEBUG() and DEBUGADD(), +as follows: +</para> + +<para><programlisting> + DEBUG( 3, ( "send_local_master_announcement: " ) ); + DEBUGADD( 3, ( "type %x for name %s ", type, global_myname ) ); + DEBUGADD( 3, ( "on subnet %s ", subrec->subnet_name ) ); + DEBUGADD( 3, ( "for workgroup %s\n", work->work_group ) ); +</programlisting></para> + +<para> +A similar, but arguably nicer approach is to use the DEBUGLVL() macro. +This macro returns True if the message level is less than or equal to +the global DEBUGLEVEL value, so: +</para> + +<para><programlisting> + if( DEBUGLVL( 3 ) ) + { + dbgtext( "send_local_master_announcement: " ); + dbgtext( "type %x for name %s ", type, global_myname ); + dbgtext( "on subnet %s ", subrec->subnet_name ); + dbgtext( "for workgroup %s\n", work->work_group ); + } +</programlisting></para> + +<para>(The dbgtext() function is explained below.)</para> + +<para>There are a few advantages to this scheme:</para> +<orderedlist> +<listitem><para> +The test is performed only once. +</para></listitem> +<listitem><para> +You can allocate variables off of the stack that will only be used +within the DEBUGLVL() block. +</para></listitem> +<listitem><para> +Processing that is only relevant to debug output can be contained +within the DEBUGLVL() block. +</para></listitem> +</orderedlist> + +</sect1> + +<sect1> +<title>New Functions</title> + +<sect2> +<title>dbgtext()</title> +<para> +This function prints debug message text to the debug file (and +possibly to syslog) via the format buffer. The function uses a +variable argument list just like printf() or Debug1(). The +input is printed into a buffer using the vslprintf() function, +and then passed to format_debug_text(). + +If you use DEBUGLVL() you will probably print the body of the +message using dbgtext(). +</para> +</sect2> + +<sect2> +<title>dbghdr()</title> +<para> +This is the function that writes a debug message header. +Headers are not processed via the format buffer. Also note that +if the format buffer is not empty, a call to dbghdr() will not +produce any output. See the comments in dbghdr() for more info. +</para> + +<para> +It is not likely that this function will be called directly. It +is used by DEBUG() and DEBUGADD(). +</para> +</sect2> + +<sect2> +<title>format_debug_text()</title> +<para> +This is a static function in debug.c. It stores the output text +for the body of the message in a buffer until it encounters a +newline. When the newline character is found, the buffer is +written to the debug file via the Debug1() function, and the +buffer is reset. This allows us to add the indentation at the +beginning of each line of the message body, and also ensures +that the output is written a line at a time (which cleans up +syslog output). +</para> +</sect2> +</sect1> +</chapter> |