NAME

       CTR0, CTR1, CTR2, CTR3, CTR4, CTR5 — kernel tracing facility

SYNOPSIS

       #include <sys/param.h>
       #include <sys/ktr.h>

       extern int ktr_cpumask;
       extern int ktr_entries;
       extern int ktr_extend;
       extern int ktr_mask;
       extern int ktr_verbose;
       extern struct ktr_entry ktr_buf[];

       void
       CTR0(u_int mask, char *format);

       void
       CTR1(u_int mask, char *format, arg1);

       void
       CTR2(u_int mask, char *format, arg1, arg2);

       void
       CTR3(u_int mask, char *format, arg1, arg2, arg3);

       void
       CTR4(u_int mask, char *format, arg1, arg2, arg3, arg4);

       void
       CTR5(u_int mask, char *format, arg1, arg2, arg3, arg4, arg5);

       void
       CTR6(u_int mask, char *format, arg1, arg2, arg3, arg4, arg5, arg6);

DESCRIPTION

       KTR  provides  a circular buffer of events that can be logged in a printf(9) style fashion.  These events
       can then be dumped with ddb(4), gdb(1) or ktrdump(8).

       Events are created and logged in the kernel via the CTRx macros.  The first parameter is a mask of  event
       types  (KTR_*) defined in <sys/ktr.h>.  The event will be logged only if any of the event types specified
       in mask are enabled in the global event mask stored in ktr_mask.  The  format  argument  is  a  printf(9)
       style  format  string  used  to build the text of the event log message.  Following the format string are
       zero to five arguments referenced by format.  Each event is logged with  a  file  name  and  source  line
       number of the originating CTR call, and a timestamp in addition to the log message.

       The  event  is stored in the circular buffer with supplied arguments as is, and formatting is done at the
       dump time.  Do not use pointers to the objects with limited lifetime, for instance, strings, because  the
       pointer may become invalid when buffer is printed.

       Note that the different macros differ only in the number of arguments each one takes, as indicated by its
       name.

       The ktr_entries variable contains the number of entries in the ktr_buf array.  These variables are mostly
       useful for post-mortem crash dump tools to locate the base of the circular trace buffer and its length.

       The ktr_mask variable contains the run time mask of events to log.

       The CPU event mask is stored in the ktr_cpumask variable.

       The  ktr_verbose  variable stores the verbose flag that controls whether events are logged to the console
       in addition to the event buffer.

EXAMPLES

       This example demonstrates the use of tracepoints at the KTR_PROC logging level.

       void
       mi_switch()
       {
               ...
               /*
                * Pick a new current process and record its start time.
                */
               ...
               CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d)", p, p->p_pid);
               ...
               cpu_switch();
               ...
               CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d)", p, p->p_pid);
               ...
       }

SEE ALSO

       ktr(4), ktrdump(8)

HISTORY

       The KTR kernel tracing facility first appeared in BSD/OS 3.0 and was imported into FreeBSD 5.0.

BUGS

       Currently there is one global buffer shared among all CPUs.  It might be profitable at some point in time
       to use per-CPU buffers instead so that if one CPU halts or starts spinning,  then  the  log  messages  it
       emitted just prior to halting or spinning will not be drowned out by events from the other CPUs.

       The  arguments  given in CTRx() macros are stored as u_long, so do not pass arguments larger than size of
       an u_long type.  For example passing 64bit arguments on 32bit architectures will give incorrect results.

Debian                                          November 30, 2008                                         KTR(9)