2 .TH trace 3 "21 October 1999" "Straylight/Edgeware" "mLib utilities library"
4 trace \- configurable tracing output
17 .B "#include <mLib/trace.h>"
19 .BI "void trace(unsigned " l ", const char *" f ", ...);"
20 .BI "void trace_block(unsigned " l ", const char *" s ,
21 .BI " const void *" b ", size_t " sz );
23 .BI "void trace_on(FILE *" fp ", unsigned " l );
24 .BI "void trace_custom(void (*" func ")(const char *" buf ,
25 .BI " size_t " sz ", void *" v ),
27 .BI "void trace_level(unsigned " l );
28 .BI "unsigned tracing(void);"
30 .BI "unsigned traceopt(const trace_opt *" t ", const char *" p ,
31 .BI " unsigned " f ", unsigned " bad );
33 .BI T( statements\fR... )
34 .BI "IF_TRACING(unsigned " l ", " statements\fR... )
39 header declares some functions and macros for handling trace output.
40 The emphasis for this system is primarily on user configurability of
41 what gets traced rather than where the output goes. That's a project
44 Each trace message is assigned a
46 by the programmer. A tracing level is set during program
47 initialization, usually by the user. A trace message is output if there
48 is a trace destination set, and the result of a bitwise AND between the
49 message level and the overall tracing level is nonzero. The idea is
50 that the programmer assigns a different bit to each group of trace
51 messages, and allows a user to select which ones are wanted.
52 .SS "Producing trace output"
55 It is passed an integer message level and a
57 format string together with arguments for the placeholders and emits the
62 formats an arbitrary block of memory as a hex dump. The arguments are,
63 in order, the message level, a pointer to the header string for the hex
64 dump, the base address of the block to dump, and the size of the block
66 .SS "Configuring trace output"
67 The tracing destination is set with the function
71 stream and a trace level to set. The stream may be null to disable
72 tracing completely (which is the default). The trace level may be set
75 which takes the new level as its single argument. The function
77 returns the current trace level, or zero if there is no trace
80 For more advanced programs, a custom output function may be provided by
82 and passing a function which will write a buffer of data somewhere
84 .SS "Parsing user trace options"
87 may be used to allow a user to set the trace level. It is passed a
88 table describing the available trace level bits, and some other
89 information, and returns a new trace level. The table consists of a
92 structures, each of which describes a bit or selection of bits which may
93 be controlled. The structure contains the following members, in order:
96 The character used to select this bit or collection of bits.
99 The level bits for this option.
101 .B "const char *help;"
102 A help string describing this option.
104 The table is terminated by an entry whose
113 Pointer to the trace options table.
116 Pointer to the user's option string.
119 The default trace options, or the previously-set options.
122 A bitmask of level bits which should be disallowed.
126 is a null pointer or contains only a
128 character, a help message is printed and the default is returned. Only
129 trace options which contain non-bad bits are displayed. Otherwise the
130 string contains option characters together with
134 which respectively turn on or off the following options; the default is
135 to turn options on. Again, only options which contain non-bad bits are
138 The `bad bit' mechanism is provided for setuid programs which in their
139 normal configuration deal with privileged information which mustn't be
140 given out to users. However, if run by someone with appropriate
141 privilege such options are safe and may be useful for debugging. The
144 mask to prevent access to secret information when running setuid, or to
146 .SS "Macro support for tracing"
147 The tracing macros are intended to make insertion of tracing information
148 unobtrusive and painless. If the
150 macro is defined, all of the tracing macros are disabled and generate no
151 code; otherwise they do their normal jobs.
155 macro simply expands to its argument. It may be wrapped around small
156 pieces of code which is only needed when compiling with tracing
157 enabled. (Larger blocks, of course, should use
158 .RB ` #ifndef NTRACE '/` #endif '
159 pairs for clarity's sake.)
161 For slightly larger code chunks which do some processing to generate
164 macro is useful. Its first argument is a message level; if the trace
165 level is set such that the message will be printed, the code in the
166 second argument is executed. If code is being compiled without tracing,
167 of course, the entire contents of the macro is ignored.
171 Mark Wooding, <mdw@nsict.org>