Starting and Controlling Trace from a Program

The AIX trace facility can be started from a program, via a subroutine call. The subroutine is trcstart and is in the librts.a library. The syntax of the trcstart subroutine is:

int trcstart(char *args)

where args is simply the options list that you would have entered for the trace command. By default, the system trace (channel 0) is started. If you want to start a generic trace, you should include a -g option in the args string. On successful completion, the trcstart subroutine returns the channel ID. For generic tracing this channel ID can be used to record to the private generic channel.

When compiling a program using this subroutine, the link to the librts.a library must be specifically requested (use -l rts as a compile option).

Controlling Trace with Trace Subroutine Calls

The controls for the trace routine are available as subroutines from the librts.a library. The subroutines return zero on successful completion. The subroutines are:

Controlling Trace with ioctl Calls

Each of the above subroutines for controlling trace:

• opens the trace control device (/dev/systrctl)
• Issues the appropriate ioctl
• closes the control device
• Returns to the calling program

To turn tracing on and off around individual sections of code, it may be more efficient for a program to issue the ioctl controls directly. This avoids the repetitive opening and closing of the trace control device. To use the ioctl interface in a program, include <sys/trcctl.h> to define the ioctl commands. The syntax of the ioctl is as follows:

ioctl
 (
fd
, 
CMD
, 
Channel
)

where:

The following code example shows how to start a trace from a program and only trace around a specified section of code:

#include <fcntl.h>
#include <sys/trcctl.h>
extern int trcstart(char *arg);
char *ctl_dev ="/dev/systrctl";
int ctl_fd;
main()
{
     printf("configuring trace collection \n");
     if (trcstart("-ad")){
         perror("trcstart");
         exit(1);
     }
   
     printf("opening the trace device \n");
     if((ctl_fd =open (ctl_dev,O_RDWR))<0){
         perror("open ctl_dev");
         exit(1);
     }
    
     printf("turning data collection on \n");
     if(ioctl(ctl_fd,TRCON,0)){
         perror("TRCON");
         exit(1);
     }
   
     /* *** code here will be traced *** */
     printf("The code to print this line will be traced.");
   
     printf("turning data collection off\n");
     if (ioctl(ctl_fd,TRCOFF,0)){
         perror("TRCOFF");
         exit(1);
     }
   
     printf("stopping the trace daemon \n");
     if (trcstop(0)){
         perror("trcstop");
         exit(1);
     }
   
     exit(0);
}

Since no output file was specified in the parameter to the trcstart() subroutine, the output of the trace will be in /var/adm/ras/trcfile, which is also the default input file of the trcrpt command.