Announce: DProbes/LTT interoperability and custom event logging

As you've probably seen from Richard's announcement, it is now possible to use the LTT/DProbes pair to dynamically insert trace points anywhere in the system.

That said, the added functionnality to LTT also enables kernel/ module programmers to dynamically add trace types and log the corresponding events in the trace.

The following functions have been added to provide this capability:
int trace_create_event
(char* /* String describing event type */,
char* /* String to format event description */,
event_data_desc* /* Table containing data formatting details */);
void trace_destroy_event

       (int           /* The event ID given by trace_create_event() */);
void trace_reregister_custom_events
       (void);

int trace_formatted_event
(int /* The event ID given by trace_create_event() */,
... /* The parameters to be printed out in the event string */);
int trace_raw_event
(int /* The event ID given by trace_create_event() */,
int /* The size of the raw data */,
void* /* Pointer to the raw event data */);

The following is an example module that uses this functionnality to log custom events in the trace:
------------------------------------------------------------------------------------
#define MODULE

#define CONFIG_TRACE

#include <linux/config.h>
#include <linux/module.h>
#include <linux/trace.h>
#include <asm/string.h>

struct delta_event
{
int an_int;
char a_char;
};

static int alpha_id, omega_id, theta_id, delta_id, rho_id;

int init_module(void)
{
uint8_t a_byte;
char a_char;
int an_int;
int a_hex;
char* a_string = "We are initializing the module"; struct delta_event a_delta_event;

/* Create events */
alpha_id = trace_create_event("Alpha",

				"Number %d, String %s, Hex %08X",
				NULL);
  omega_id = trace_create_event("Omega",
				"Number %d, Char %c",
				NULL);
  theta_id = trace_create_event("Theta",
				"Plain string",
				NULL);
  delta_id = trace_create_event("Delta",
				NULL,
				NULL);
  rho_id = trace_create_event("Rho",
			      NULL,
			      NULL);

  /* Trace events */
  an_int = 1;
  a_hex = 0xFFFFAAAA;
  trace_formatted_event(alpha_id, an_int, a_string, a_hex);
  an_int = 25;
  a_char = 'c';
  trace_formatted_event(omega_id, an_int, a_char);
  trace_formatted_event(theta_id);
  memset(&a_delta_event, 0, sizeof(a_delta_event));
  trace_raw_event(delta_id, sizeof(a_delta_event), &a_delta_event);
  a_byte = 0x12;
  trace_raw_event(rho_id, sizeof(a_byte), &a_byte);

return 0;
}

void cleanup_module(void)
{
uint8_t a_byte;
char a_char;
int an_int;
int a_hex;
char* a_string = "We are initializing the module"; struct delta_event a_delta_event;

  /* Trace events */
  an_int = 324;
  a_hex = 0xABCDEF10;
  trace_formatted_event(alpha_id, an_int, a_string, a_hex);
  an_int = 789;
  a_char = 's';
  trace_formatted_event(omega_id, an_int, a_char);
  trace_formatted_event(theta_id);
  memset(&a_delta_event, 0xFF, sizeof(a_delta_event));
  trace_raw_event(delta_id, sizeof(a_delta_event), &a_delta_event);
  a_byte = 0xA4;
  trace_raw_event(rho_id, sizeof(a_byte), &a_byte);

/* Destroy the events created */
trace_destroy_event(alpha_id);
trace_destroy_event(omega_id);
trace_destroy_event(theta_id);
trace_destroy_event(delta_id);
trace_destroy_event(rho_id);
}
------------------------------------------------------------------------------------

This is the resulting output in the trace dump:
Memory 975,040,616,826,952 494 14 PAGE ALLOC ORDER : 0
Memory 975,040,616,826,957 494 14 PAGE FREE ORDER : 0
Memory 975,040,616,826,958 494 14 PAGE FREE ORDER : 0
Event creation 975,040,616,826,964 494 146 NEW EVENT TYPE : Alpha
Event creation 975,040,616,826,967 494 146 NEW EVENT TYPE : Omega
Event creation 975,040,616,826,970 494 146 NEW EVENT TYPE : Theta
Event creation 975,040,616,826,972 494 146 NEW EVENT TYPE : Delta
Event creation 975,040,616,826,974 494 146 NEW EVENT TYPE : Rho
Alpha 975,040,616,826,988 494 80 Number 1, String We are initializing the module, Hex FFFFAAAA
Omega 975,040,616,826,991 494 36 Number 25, Char c
Theta 975,040,616,826,993 494 31 Plain string
Delta 975,040,616,826,994 494 26 00 00 00 00 00 00 00 00
Rho 975,040,616,826,995 494 19 12
Syscall exit 975,040,616,826,996 494 6
Syscall entry 975,040,616,827,028 494 14 SYSCALL : close; EIP : 0x0804AE41

You can find more info on this custom event logging capability on LTT's web site at: http://www.opersys.com/LTT

You can find DProbes at:
http://oss.software.ibm.com/developer/opensource/linux/projects/dprobes/

Best regards

Karim

===================================================
Karim Yaghmour
[email protected]
Operating System Consultant
(Linux kernel, real-time and distributed systems)
===================================================
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