Examples--Defining TNF Types

Example 1-5 shows how a new TNF type is defined and used in a probe.

Example 1-5 is assumed to be part of a fictitious library called libpalloc.so that uses the prefix pal for all its symbols.

Example 1-5 Defining a new TNF type

#include <tnf/probe.h>

typedef struct pal_header {
        long    size;
        char * descriptor;
        struct pal_header *next;
} pal_header_t;

TNF_DECLARE_RECORD(pal_header_t, pal_tnf_header);
TNF_DEFINE_RECORD_2(pal_header_t, pal_tnf_header,
                        tnf_long,   size,
                        tnf_string, descriptor)

/* 
 * Note: name space prefixed by pal_tnf_header should not be  * used by this client any more.
 */

void 
pal_free(pal_header_t *header_p)
{
        int state;

        TNF_PROBE_2(pal_free_start, "palloc pal_free",
                "sunw%debug entering pal_free",
                tnf_long,       state_var, state,
                pal_tnf_header, header_var, header_p);
        . . .
}

It is possible to make a tnf_type definition recursive or mutually recursive, such as in a structure that uses the next field to point to itself (a linked list).

When such a structure is sent in to a TNF_PROBE, then the entire linked list is logged to the trace file (until the next field is NULL). But, when the list is circular, it results in an infinite loop. To break the recursion, either omit the next field from the tnf_type, or define the type of the next member as tnf_opaque.