The
ktrace() function enables or disables tracing of one or more processes. Users may only trace their own processes. Only the super-user can trace setuid or setgid programs.
The
tracefile gives the pathname of the file to be used for tracing. The file must exist and be writable by the calling process. All trace records are always appended to the file, so the file must be truncated to zero length to discard previous trace data. If tracing points are being disabled (see KTROP_CLEAR below),
tracefile may be NULL. If using
fktrace() then instead of passing a filename as
tracefile, a file descriptor is passed as
fd and behaviour is otherwise the same.
The
ops parameter specifies the requested ktrace operation. The defined operations are:
KTROP_SET
Enable trace points specified in trpoints.
KTROP_CLEAR
Disable trace points specified in trpoints.
KTROP_CLEARFILE
Stop all tracing.
KTRFLAG_DESCEND
The tracing change should apply to the specified process and all its current children.
The
trpoints parameter specifies the trace points of interest. The defined trace points are:
KTRFAC_SYSCALL
Trace system calls.
KTRFAC_SYSRET
Trace return values from system calls.
KTRFAC_NAMEI
Trace name lookup operations.
KTRFAC_GENIO
Trace all I/O (note that this option can generate much output).
KTRFAC_PSIG
Trace posted signals.
KTRFAC_CSW
Trace context switch points.
KTRFAC_EMUL
Trace emulation changes.
KTRFAC_INHERIT
Inherit tracing to future children.
Each tracing event outputs a record composed of a generic header followed by a trace point specific structure. The generic header is:
struct ktr_header {
int ktr_len; /* length of buf */
short ktr_type; /* trace record type */
pid_t ktr_pid; /* process id */
char ktr_comm[MAXCOMLEN+1]; /* command name */
struct timeval ktr_time; /* timestamp */
caddr_t ktr_buf;
};
The
ktr_len field specifies the length of the
ktr_type data that follows this header. The
ktr_pid and
ktr_comm fields specify the process and command generating the record. The
ktr_time field gives the time (with microsecond resolution) that the record was generated. The
ktr_buf is an internal kernel pointer and is not useful.
The generic header is followed by
ktr_len bytes of a
ktr_type record. The type specific records are defined in the
<sys/ktrace.h> include file.