Hi all,
I refer this post to write a simple script to trace fork system call.
The C program is like this:
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main(void) {
pid_t pid = 0;
pid = fork();
if (pid > 0) {
printf("Parent:%d\n", time(NULL));
} else if (pid == 0) {
printf("Child:%d\n", time(NULL));
}
return 0;
}
The DTrace script is like this (debug.d):
#!/usr/sbin/dtrace -ws
proc:::start
/ppid == $target/
{
stop();
printf("fork %d\n", pid);
system("./debug.d -p %d", pid);
}
pid$target:libc:time:return
{
trace(arg1);
ustack();
}
The execution and output are like the following:
bash-3.2# ./debug.d -c ./fork
dtrace: script './debug.d' matched 2 probes
dtrace: allowing destructive actions
Parent:1414458615
dtrace: pid 709 has exited
CPU ID FUNCTION:NAME
6 910 lwp_rtt_initial:start fork 710
dtrace: script './debug.d' matched 2 probes
dtrace: allowing destructive actions
Child:1414458616
dtrace: pid 710 has exited
CPU ID FUNCTION:NAME
7 58632 time:return 1414458616
libc.so.1`time+0x22
fork`_start+0x80
10 58627 time:return 1414458615
libc.so.1`time+0x22
fork`_start+0x80
From the explanation of stop action, it only refers "the process that
fires the enabled probe to stop when it next leaves the kernel". But from the
above output, we can see both parent and child processes have exited.
My question is when a process is stopped by stop() action, when and how
does the process is restarted?
Thanks very much in advance!
Best Regards
Nan Xiao
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