source: trunk/samba/docs/htmldocs/Samba3-Developers-Guide/debug.html @ 30

Last change on this file since 30 was 1, checked in by Paul Smedley, 15 years ago

Initial code import

File size: 11.5 KB
Line 
1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 4. The samba DEBUG system</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.68.1"><link rel="start" href="index.html" title="SAMBA Developers Guide"><link rel="up" href="pt02.html" title="Part II. Samba Basics"><link rel="prev" href="architecture.html" title="Chapter 3. Samba Architecture"><link rel="next" href="internals.html" title="Chapter 5. Samba Internals"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4. The samba DEBUG system</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="architecture.html">Prev</a> </td><th width="60%" align="center">Part II. Samba Basics</th><td width="20%" align="right"> <a accesskey="n" href="internals.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="debug"></a>Chapter 4. The samba DEBUG system</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Chris</span> <span class="surname">Hertel</span></h3></div></div><div><p class="pubdate">July 1998</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="debug.html#id292560">New Output Syntax</a></span></dt><dt><span class="sect1"><a href="debug.html#id292660">The DEBUG() Macro</a></span></dt><dt><span class="sect1"><a href="debug.html#id292752">The DEBUGADD() Macro</a></span></dt><dt><span class="sect1"><a href="debug.html#id292784">The DEBUGLVL() Macro</a></span></dt><dt><span class="sect1"><a href="debug.html#id292862">New Functions</a></span></dt><dd><dl><dt><span class="sect2"><a href="debug.html#id292867">dbgtext()</a></span></dt><dt><span class="sect2"><a href="debug.html#id292881">dbghdr()</a></span></dt><dt><span class="sect2"><a href="debug.html#id292897">format_debug_text()</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id292560"></a>New Output Syntax</h2></div></div></div><p>
2   The syntax of a debugging log file is represented as:
3</p><pre class="programlisting">
4  &gt;debugfile&lt; :== { &gt;debugmsg&lt; }
5
6  &gt;debugmsg&lt;  :== &gt;debughdr&lt; '\n' &gt;debugtext&lt;
7
8  &gt;debughdr&lt;  :== '[' TIME ',' LEVEL ']' FILE ':' [FUNCTION] '(' LINE ')'
9
10  &gt;debugtext&lt; :== { &gt;debugline&lt; }
11
12  &gt;debugline&lt; :== TEXT '\n'
13</pre><p>
14TEXT is a string of characters excluding the newline character.
15</p><p>
16LEVEL is the DEBUG level of the message (an integer in the range
17                0..10).
18</p><p>
19TIME is a timestamp.
20</p><p>
21FILE is the name of the file from which the debug message was
22generated.
23</p><p>
24FUNCTION is the function from which the debug message was generated.
25</p><p>
26LINE is the line number of the debug statement that generated the
27message.
28</p><p>Basically, what that all means is:</p><div class="orderedlist"><ol type="1"><li><p>
29A debugging log file is made up of debug messages.
30</p></li><li><p>
31Each debug message is made up of a header and text. The header is
32separated from the text by a newline.
33</p></li><li><p>
34The header begins with the timestamp and debug level of the
35message enclosed in brackets. The filename, function, and line
36number at which the message was generated follow. The filename is
37terminated by a colon, and the function name is terminated by the
38parenthesis which contain the line number. Depending upon the
39compiler, the function name may be missing (it is generated by the
40__FUNCTION__ macro, which is not universally implemented, dangit).
41</p></li><li><p>
42The message text is made up of zero or more lines, each terminated
43by a newline.
44</p></li></ol></div><p>Here's some example output:</p><pre class="programlisting">
45    [1998/08/03 12:55:25, 1] nmbd.c:(659)
46      Netbios nameserver version 1.9.19-prealpha started.
47      Copyright Andrew Tridgell 1994-1997
48    [1998/08/03 12:55:25, 3] loadparm.c:(763)
49      Initializing global parameters
50</pre><p>
51Note that in the above example the function names are not listed on
52the header line. That's because the example above was generated on an
53SGI Indy, and the SGI compiler doesn't support the __FUNCTION__ macro.
54</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id292660"></a>The DEBUG() Macro</h2></div></div></div><p>
55Use of the DEBUG() macro is unchanged. DEBUG() takes two parameters.
56The first is the message level, the second is the body of a function
57call to the Debug1() function.
58</p><p>That's confusing.</p><p>Here's an example which may help a bit. If you would write</p><pre class="programlisting">
59printf( "This is a %s message.\n", "debug" );
60</pre><p>
61to send the output to stdout, then you would write
62</p><pre class="programlisting">
63DEBUG( 0, ( "This is a %s message.\n", "debug" ) );
64</pre><p>
65to send the output to the debug file.  All of the normal printf()
66formatting escapes work.
67</p><p>
68Note that in the above example the DEBUG message level is set to 0.
69Messages at level 0 always print.  Basically, if the message level is
70less than or equal to the global value DEBUGLEVEL, then the DEBUG
71statement is processed.
72</p><p>
73The output of the above example would be something like:
74</p><pre class="programlisting">
75    [1998/07/30 16:00:51, 0] file.c:function(128)
76      This is a debug message.
77</pre><p>
78Each call to DEBUG() creates a new header *unless* the output produced
79by the previous call to DEBUG() did not end with a '\n'. Output to the
80debug file is passed through a formatting buffer which is flushed
81every time a newline is encountered. If the buffer is not empty when
82DEBUG() is called, the new input is simply appended.
83</p><p>
84...but that's really just a Kludge. It was put in place because
85DEBUG() has been used to write partial lines. Here's a simple (dumb)
86example of the kind of thing I'm talking about:
87</p><pre class="programlisting">
88    DEBUG( 0, ("The test returned " ) );
89    if( test() )
90      DEBUG(0, ("True") );
91    else
92      DEBUG(0, ("False") );
93    DEBUG(0, (".\n") );
94</pre><p>
95Without the format buffer, the output (assuming test() returned true)
96would look like this:
97</p><pre class="programlisting">
98    [1998/07/30 16:00:51, 0] file.c:function(256)
99      The test returned
100    [1998/07/30 16:00:51, 0] file.c:function(258)
101      True
102    [1998/07/30 16:00:51, 0] file.c:function(261)
103      .
104</pre><p>Which isn't much use. The format buffer kludge fixes this problem.
105</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id292752"></a>The DEBUGADD() Macro</h2></div></div></div><p>
106In addition to the kludgey solution to the broken line problem
107described above, there is a clean solution. The DEBUGADD() macro never
108generates a header. It will append new text to the current debug
109message even if the format buffer is empty. The syntax of the
110DEBUGADD() macro is the same as that of the DEBUG() macro.
111</p><pre class="programlisting">
112    DEBUG( 0, ("This is the first line.\n" ) );
113    DEBUGADD( 0, ("This is the second line.\nThis is the third line.\n" ) );
114</pre><p>Produces</p><pre class="programlisting">
115    [1998/07/30 16:00:51, 0] file.c:function(512)
116      This is the first line.
117      This is the second line.
118      This is the third line.
119</pre></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id292784"></a>The DEBUGLVL() Macro</h2></div></div></div><p>
120One of the problems with the DEBUG() macro was that DEBUG() lines
121tended to get a bit long. Consider this example from
122nmbd_sendannounce.c:
123</p><pre class="programlisting">
124  DEBUG(3,("send_local_master_announcement: type %x for name %s on subnet %s for workgroup %s\n",
125            type, global_myname, subrec-&gt;subnet_name, work-&gt;work_group));
126</pre><p>
127One solution to this is to break it down using DEBUG() and DEBUGADD(),
128as follows:
129</p><pre class="programlisting">
130  DEBUG( 3, ( "send_local_master_announcement: " ) );
131  DEBUGADD( 3, ( "type %x for name %s ", type, global_myname ) );
132  DEBUGADD( 3, ( "on subnet %s ", subrec-&gt;subnet_name ) );
133  DEBUGADD( 3, ( "for workgroup %s\n", work-&gt;work_group ) );
134</pre><p>
135A similar, but arguably nicer approach is to use the DEBUGLVL() macro.
136This macro returns True if the message level is less than or equal to
137the global DEBUGLEVEL value, so:
138</p><pre class="programlisting">
139  if( DEBUGLVL( 3 ) )
140    {
141    dbgtext( "send_local_master_announcement: " );
142    dbgtext( "type %x for name %s ", type, global_myname );
143    dbgtext( "on subnet %s ", subrec-&gt;subnet_name );
144    dbgtext( "for workgroup %s\n", work-&gt;work_group );
145    }
146</pre><p>(The dbgtext() function is explained below.)</p><p>There are a few advantages to this scheme:</p><div class="orderedlist"><ol type="1"><li><p>
147The test is performed only once.
148</p></li><li><p>
149You can allocate variables off of the stack that will only be used
150within the DEBUGLVL() block.
151</p></li><li><p>
152Processing that is only relevant to debug output can be contained
153within the DEBUGLVL() block.
154</p></li></ol></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id292862"></a>New Functions</h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id292867"></a>dbgtext()</h3></div></div></div><p>
155This function prints debug message text to the debug file (and
156possibly to syslog) via the format buffer. The function uses a
157variable argument list just like printf() or Debug1(). The
158input is printed into a buffer using the vslprintf() function,
159and then passed to format_debug_text().
160
161If you use DEBUGLVL() you will probably print the body of the
162message using dbgtext().
163</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id292881"></a>dbghdr()</h3></div></div></div><p>
164This is the function that writes a debug message header.
165Headers are not processed via the format buffer. Also note that
166if the format buffer is not empty, a call to dbghdr() will not
167produce any output. See the comments in dbghdr() for more info.
168</p><p>
169It is not likely that this function will be called directly. It
170is used by DEBUG() and DEBUGADD().
171</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id292897"></a>format_debug_text()</h3></div></div></div><p>
172This is a static function in debug.c. It stores the output text
173for the body of the message in a buffer until it encounters a
174newline. When the newline character is found, the buffer is
175written to the debug file via the Debug1() function, and the
176buffer is reset. This allows us to add the indentation at the
177beginning of each line of the message body, and also ensures
178that the output is written a line at a time (which cleans up
179syslog output).
180</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="architecture.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="pt02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="internals.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 3. Samba Architecture </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 5. Samba Internals</td></tr></table></div></body></html>
Note: See TracBrowser for help on using the repository browser.