Chapter 4. The samba DEBUG system

Chapter 4. The samba DEBUG system
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Chris Hertel

July 1998

Table of Contents

New Output Syntax

The DEBUG() Macro

The DEBUGADD() Macro

The DEBUGLVL() Macro

New Functions

dbgtext()
dbghdr()
format_debug_text()

New Output Syntax

- The syntax of a debugging log file is represented as: -

-  >debugfile< :== { >debugmsg< }
-
-  >debugmsg<  :== >debughdr< '\n' >debugtext<
-
-  >debughdr<  :== '[' TIME ',' LEVEL ']' FILE ':' [FUNCTION] '(' LINE ')'
-
-  >debugtext< :== { >debugline< }
-
-  >debugline< :== TEXT '\n'
-

-TEXT is a string of characters excluding the newline character. -

-LEVEL is the DEBUG level of the message (an integer in the range - 0..10). -

-TIME is a timestamp. -

-FILE is the name of the file from which the debug message was -generated. -

-FUNCTION is the function from which the debug message was generated. -

-LINE is the line number of the debug statement that generated the -message. -

Basically, what that all means is:

-A debugging log file is made up of debug messages. -
-Each debug message is made up of a header and text. The header is -separated from the text by a newline. -
-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). -
-The message text is made up of zero or more lines, each terminated -by a newline. -

Here's some example output:

-    [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
-

-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. -

The DEBUG() Macro

-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. -

That's confusing.

Here's an example which may help a bit. If you would write

-printf( "This is a %s message.\n", "debug" );
-

-to send the output to stdout, then you would write -

-DEBUG( 0, ( "This is a %s message.\n", "debug" ) );
-

-to send the output to the debug file. All of the normal printf() -formatting escapes work. -

-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. -

-The output of the above example would be something like: -

-    [1998/07/30 16:00:51, 0] file.c:function(128)
-      This is a debug message.
-

-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. -

-...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: -

-    DEBUG( 0, ("The test returned " ) );
-    if( test() )
-      DEBUG(0, ("True") );
-    else
-      DEBUG(0, ("False") );
-    DEBUG(0, (".\n") );
-

-Without the format buffer, the output (assuming test() returned true) -would look like this: -

-    [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)
-      .
-

Which isn't much use. The format buffer kludge fixes this problem. -

The DEBUGADD() Macro

-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. -

-    DEBUG( 0, ("This is the first line.\n" ) );
-    DEBUGADD( 0, ("This is the second line.\nThis is the third line.\n" ) );
-

Produces

-    [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.
-

The DEBUGLVL() Macro

-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: -

-  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));
-

-One solution to this is to break it down using DEBUG() and DEBUGADD(), -as follows: -

-  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 ) );
-

-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: -

-  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 );
-    }
-

(The dbgtext() function is explained below.)

There are a few advantages to this scheme:

-The test is performed only once. -
-You can allocate variables off of the stack that will only be used -within the DEBUGLVL() block. -
-Processing that is only relevant to debug output can be contained -within the DEBUGLVL() block. -

New Functions

dbgtext()

-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(). -

dbghdr()

-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. -

-It is not likely that this function will be called directly. It -is used by DEBUG() and DEBUGADD(). -

format_debug_text()

-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). -

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