task_struct's real_parent vs parent members

task_struct's real_parent vs parent members

[Vimal]

Hi,

I am looking through kernel 3.2's task_struct, which has two pointers
for parents:  real_parent and parent
(http://lxr.free-electrons.com/source/include/linux/sched.h#L1313)   I
would like to know why there are two pointers, and how these two
differ.

init_task's parent and real_parent are initialised to point to itself.
 Since the main way processes are created is through fork()/clone(), I
tried following do_fork function to see where a newly created
process's parent is set, but I am unable to find it.  I see that
do_fork dups the current task_struct, and only updates the new
process's real_parent, depending on flags (passed via clone/fork
syscall).

The documentation in sched.h:1313 says that "parent" refers to the
parent task that would receive SIGCHLD (i.e., the one that issues
wait4()).  I followed the wait4() syscall to do_wait(), I still am not
able to find where the task's parent is updated.

Is there something I'm missing?

Thanks,
-- 
Vimal

task_struct's real_parent vs parent members

[Mulyadi Santosa]

Hi Vimal...

On Mon, Feb 27, 2012 at 03:40, Vimal <j.vimal@gmail.com> wrote:
> The documentation in sched.h:1313 says that "parent" refers to the
> parent task that would receive SIGCHLD (i.e., the one that issues
> wait4()). ?I followed the wait4() syscall to do_wait(), I still am not
> able to find where the task's parent is updated.

I am bit rusty here, but AFAIK sigchld is thrown to the process who
ptrace another process. CMIIW

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

task_struct's real_parent vs parent members

[Vimal]

Hi Mulyadi,

On 26 February 2012 23:48, Mulyadi Santosa <mulyadi.santosa@gmail.com> wrote:
> I am bit rusty here, but AFAIK sigchld is thrown to the process who
> ptrace another process. CMIIW
>

sigchld's definition [1] says it's sent to the parent process when a
child terminates.

But I do agree that the notion of a parent seems a bit ambiguous when
a process is being ptraced.

ptrace is what I found when looking through some websites, and you may
very well be correct.   But as always, it is good to confirm through
code. :)   Let me try checking the ptrace functions.

Thanks!
-- 
Vimal

task_struct's real_parent vs parent members

[Vimal]

Hi Mulyadi,

You were right.   I found this code, which is called from
ptrace_attach function:

http://lxr.free-electrons.com/source/kernel/ptrace.c#L41

Thanks :)

On 27 February 2012 08:45, Vimal <j.vimal@gmail.com> wrote:
> Hi Mulyadi,
>
> On 26 February 2012 23:48, Mulyadi Santosa <mulyadi.santosa@gmail.com> wrote:
>> I am bit rusty here, but AFAIK sigchld is thrown to the process who
>> ptrace another process. CMIIW
>>
>
> sigchld's definition [1] says it's sent to the parent process when a
> child terminates.
>
> But I do agree that the notion of a parent seems a bit ambiguous when
> a process is being ptraced.
>
> ptrace is what I found when looking through some websites, and you may
> very well be correct. ? But as always, it is good to confirm through
> code. :) ? Let me try checking the ptrace functions.
>
> Thanks!
> --
> Vimal



-- 
Vimal

task_struct's real_parent vs parent members

[Mulyadi Santosa]

On Tue, Feb 28, 2012 at 03:58, Vimal <j.vimal@gmail.com> wrote:
> Hi Mulyadi,
>
> You were right. ? I found this code, which is called from
> ptrace_attach function:
>
> http://lxr.free-electrons.com/source/kernel/ptrace.c#L41


Phewwww :) Like I said.... i am getting rusty :) glad to help btw :D

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com