dtrace discuss - Mar 2008 - how to print process name in BEGIN ?

My dtrace script should be started with -p pid or  -c command.  When it starts,
I want to print a banner showing the pid and the name of that process.

BEGIN
{
  Version = "x0.4";
  start = timestamp;
  printf("ver %s - monitoring process %s[%d] - started %Y\n", Version,
execname, $target, walltimestamp);
  printf("\nPress Ctrl/C to end sampling\n\n");
}

But execname is always dtrace in the BEGIN{}.

Any way to get the name of the process pointed to by $target ?


--
This message posted from opensolaris.org

On Mon, Mar 10, 2008 at 09:25:44AM -0700, Kelly Caudill
wrote:
> My dtrace script should be started with -p pid or  -c command.  When it
> starts, I want to print a banner showing the pid and the name of that
process.
> 
> BEGIN
> {
>   Version = "x0.4";
>   start = timestamp;
>   printf("ver %s - monitoring process %s[%d] - started %Y\n",
Version, execname, $target, walltimestamp);
>   printf("\nPress Ctrl/C to end sampling\n\n");
> }
> 
> But execname is always dtrace in the BEGIN{}.
> 
> Any way to get the name of the process pointed to by $target ?
There''s no good built-in support for that though it would probably be a
good
RFE to files. You can do the translation yourself, but it involves walking a
hash chain so you will need to choose a fixed depth in your D script.

---8<---

BEGIN
{
        this->pidp = `pidhash[$target & (`pid_hashsz - 1)];
        this->pidname = "<error>";
}

/* repeat this clause to accommodate longer hash chains. */
BEGIN
/this->pidp->pid_id != $target && this->pidp->pid_link != 0/
{
        this->pidp = this->pidp->pid_link;
}

BEGIN
/this->pidp->pid_id != $target && this->pidp->pid_link == 0/
{
        this->pidname = "<no such process>";
}

BEGIN
/this->pidp->pid_id != $target && this->pidp->pid_link != 0/
{
        this->pidname = "<hash chain too long>";
}

BEGIN
/this->pidp->pid_id == $target/
{
        /* workaround for 6465277 */
        this->slot = (*(uint32_t *)this->pidp) >> 8;
        this->pidname = `procdir[this->slot].pe_proc->p_user.u_comm;
}

BEGIN
{
        printf("%d %s", $target, this->pidname);
}

--->8---

Hardly beatiful, but it works... which has become something of a DTrace
mantra for some of these stickier corner cases.

Adam

-- 
Adam Leventhal, Fishworks                        http://blogs.sun.com/ahl