* -1 pid on sys.wait4?
@ 2012-11-09 19:53 Nicholas Murphy
2012-11-09 19:59 ` Josh Stone
0 siblings, 1 reply; 3+ messages in thread
From: Nicholas Murphy @ 2012-11-09 19:53 UTC (permalink / raw)
To: systemtap
Maybe a dumb question, but: why would $pid show up as -1 fairly consistently in a "probe kernel.function("sys_wait4").call" probe?
Thanks,
Nick
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: -1 pid on sys.wait4?
2012-11-09 19:53 -1 pid on sys.wait4? Nicholas Murphy
@ 2012-11-09 19:59 ` Josh Stone
2012-11-09 20:07 ` Nicholas Murphy
0 siblings, 1 reply; 3+ messages in thread
From: Josh Stone @ 2012-11-09 19:59 UTC (permalink / raw)
To: systemtap
On 11/09/2012 11:53 AM, Nicholas Murphy wrote:
> Maybe a dumb question, but: why would $pid show up as -1 fairly
> consistently in a "probe kernel.function("sys_wait4").call" probe?
Check out "man 2 wait", which says:
The value of pid can be:
< -1 meaning wait for any child process whose process group ID is
equal to the absolute value of pid.
-1 meaning wait for any child process.
0 meaning wait for any child process whose process group ID is
equal to that of the calling process.
> 0 meaning wait for the child whose process ID is equal to the
value of pid.
So it just means that the sys_wait4 caller was not specific about which
child process they're waiting for.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: -1 pid on sys.wait4?
2012-11-09 19:59 ` Josh Stone
@ 2012-11-09 20:07 ` Nicholas Murphy
0 siblings, 0 replies; 3+ messages in thread
From: Nicholas Murphy @ 2012-11-09 20:07 UTC (permalink / raw)
To: Josh Stone; +Cc: systemtap
So, yes, dumb question. :) (sorry...confused myself between $pid and pid())
Thanks,
Nick
On Nov 9, 2012, at 2:59 PM, Josh Stone <jistone@redhat.com> wrote:
> On 11/09/2012 11:53 AM, Nicholas Murphy wrote:
>> Maybe a dumb question, but: why would $pid show up as -1 fairly
>> consistently in a "probe kernel.function("sys_wait4").call" probe?
>
> Check out "man 2 wait", which says:
>
> The value of pid can be:
>
> < -1 meaning wait for any child process whose process group ID is
> equal to the absolute value of pid.
>
> -1 meaning wait for any child process.
>
> 0 meaning wait for any child process whose process group ID is
> equal to that of the calling process.
>
>> 0 meaning wait for the child whose process ID is equal to the
> value of pid.
>
>
> So it just means that the sys_wait4 caller was not specific about which
> child process they're waiting for.
^ permalink raw reply [flat|nested] 3+ messages in thread
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