inotify and /proc/<pid>

inotify and /proc/<pid>

[Joseph Pingenot]

I was trying to use inotify to watch process changes (especially process
  termination) by watching /proc/<pid>.

Sadly, although I could see something reading various files, nothing
  was issued when the process I was watching exited and the directory
  went away.

Is this intentional, or a bug?

-Joseph
-- 
trelane@digitasaru.net.///////////////////////////////////////////////
"There is also an entire branch in the physical therapy field dedicated
 to the treatment of little-finger injuries caused by excessive Emacs
 use."  --Linux Weekly News editor (http://lwn.net/Articles/206916/)
///////260 IATL / The University of Iowa / Iowa City, IA  52242///////

Re: inotify and /proc/<pid>

[Al Viro]

On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
> I was trying to use inotify to watch process changes (especially process
>   termination) by watching /proc/<pid>.
> 
> Sadly, although I could see something reading various files, nothing
>   was issued when the process I was watching exited and the directory
>   went away.
> 
> Is this intentional, or a bug?

It's a bug you intend to introduce in your program...  IOW, don't
do that.

Re: inotify and /proc/<pid>

[Joseph Pingenot]

>From Al Viro on Tuesday, 31 July, 2007:
>On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
>> I was trying to use inotify to watch process changes (especially process
>>   termination) by watching /proc/<pid>.
>> Sadly, although I could see something reading various files, nothing
>>   was issued when the process I was watching exited and the directory
>>   went away.
>> Is this intentional, or a bug?
>It's a bug you intend to introduce in your program...  IOW, don't
>do that.

More background, please?

What's the way to check for a process exiting without spinning?

-Joseph

-- 
trelane@digitasaru.net.///////////////////////////////////////////////
"There is also an entire branch in the physical therapy field dedicated
 to the treatment of little-finger injuries caused by excessive Emacs
 use."  --Linux Weekly News editor (http://lwn.net/Articles/206916/)
///////260 IATL / The University of Iowa / Iowa City, IA  52242///////

Re: inotify and /proc/<pid>

[Joseph Pingenot]

>From Joseph Pingenot on Monday, 30 July, 2007:
>From Al Viro on Tuesday, 31 July, 2007:
>>On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
>>> I was trying to use inotify to watch process changes (especially process
>>>   termination) by watching /proc/<pid>.
>>> Sadly, although I could see something reading various files, nothing
>>>   was issued when the process I was watching exited and the directory
>>>   went away.
>>> Is this intentional, or a bug?
>>It's a bug you intend to introduce in your program...  IOW, don't
>>do that.
>More background, please?
>What's the way to check for a process exiting without spinning?

I should also specify that the process being waited on is not a
  child process-it's just some other process on the system.

-- 
trelane@digitasaru.net.///////////////////////////////////////////////
"There is also an entire branch in the physical therapy field dedicated
 to the treatment of little-finger injuries caused by excessive Emacs
 use."  --Linux Weekly News editor (http://lwn.net/Articles/206916/)
///////260 IATL / The University of Iowa / Iowa City, IA  52242///////

Re: inotify and /proc/<pid>

[Al Viro]

On Mon, Jul 30, 2007 at 10:31:13PM -0500, Joseph Pingenot wrote:
> >From Joseph Pingenot on Monday, 30 July, 2007:
> >From Al Viro on Tuesday, 31 July, 2007:
> >>On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
> >>> I was trying to use inotify to watch process changes (especially process
> >>>   termination) by watching /proc/<pid>.
> >>> Sadly, although I could see something reading various files, nothing
> >>>   was issued when the process I was watching exited and the directory
> >>>   went away.
> >>> Is this intentional, or a bug?
> >>It's a bug you intend to introduce in your program...  IOW, don't
> >>do that.
> >More background, please?
> >What's the way to check for a process exiting without spinning?
> 
> I should also specify that the process being waited on is not a
>   child process-it's just some other process on the system.

Umm...  Any details on intended use?  IOW, is that "I want to write
an utility that would wait for given PID to exit, just for the hell
of it" or is there something you are trying to implement using that?

Re: inotify and /proc/<pid>

[Joseph Pingenot]

>From Al Viro on Tuesday, 31 July, 2007:
>On Mon, Jul 30, 2007 at 10:31:13PM -0500, Joseph Pingenot wrote:
>> >From Joseph Pingenot on Monday, 30 July, 2007:
>> >From Al Viro on Tuesday, 31 July, 2007:
>> >>On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
>> >>> I was trying to use inotify to watch process changes (especially process
>> >>>   termination) by watching /proc/<pid>.
>> >>> Sadly, although I could see something reading various files, nothing
>> >>>   was issued when the process I was watching exited and the directory
>> >>>   went away.
>> >>> Is this intentional, or a bug?
>> >>It's a bug you intend to introduce in your program...  IOW, don't
>> >>do that.
>> >More background, please?
>> >What's the way to check for a process exiting without spinning?
>> I should also specify that the process being waited on is not a
>>   child process-it's just some other process on the system.
>Umm...  Any details on intended use?  IOW, is that "I want to write
>an utility that would wait for given PID to exit, just for the hell
>of it" or is there something you are trying to implement using that?

I'm trying to implement pwait.  It blocks until a specified PID exits,
  and then it exits.

You can use it to do other stuff after a program finishes.

While we're on the subject, is there some way to receive notification
  that some aspect of a process changes (in this case, stopping using
  CPU, but not exiting).

Thanks for the time to help me figure this out.

-Joseph

-- 
trelane@digitasaru.net.///////////////////////////////////////////////
"There is also an entire branch in the physical therapy field dedicated
 to the treatment of little-finger injuries caused by excessive Emacs
 use."  --Linux Weekly News editor (http://lwn.net/Articles/206916/)
///////260 IATL / The University of Iowa / Iowa City, IA  52242///////

Re: inotify and /proc/<pid>

[Kyle McMartin]

On Mon, Jul 30, 2007 at 10:40:59PM -0500, Joseph Pingenot wrote:
> From Al Viro on Tuesday, 31 July, 2007:
> >On Mon, Jul 30, 2007 at 10:31:13PM -0500, Joseph Pingenot wrote:
> >> >From Joseph Pingenot on Monday, 30 July, 2007:
> >> >From Al Viro on Tuesday, 31 July, 2007:
> >> >>On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
> >> >>> I was trying to use inotify to watch process changes (especially process
> >> >>>   termination) by watching /proc/<pid>.
> >> >>> Sadly, although I could see something reading various files, nothing
> >> >>>   was issued when the process I was watching exited and the directory
> >> >>>   went away.
> >> >>> Is this intentional, or a bug?
> >> >>It's a bug you intend to introduce in your program...  IOW, don't
> >> >>do that.
> >> >More background, please?
> >> >What's the way to check for a process exiting without spinning?
> >> I should also specify that the process being waited on is not a
> >>   child process-it's just some other process on the system.
> >Umm...  Any details on intended use?  IOW, is that "I want to write
> >an utility that would wait for given PID to exit, just for the hell
> >of it" or is there something you are trying to implement using that?
> 
> I'm trying to implement pwait.  It blocks until a specified PID exits,
>   and then it exits.
>

ptrace with options set to PTRACE_O_TRACEEXIT?

--Kyle

Re: inotify and /proc/<pid>

[Al Viro]

On Mon, Jul 30, 2007 at 10:40:59PM -0500, Joseph Pingenot wrote:
> I'm trying to implement pwait.  It blocks until a specified PID exits,
>   and then it exits.

er... ptrace(2)?

Re: inotify and /proc/<pid>

[Joseph Pingenot]

>From Al Viro on Tuesday, 31 July, 2007:
>On Mon, Jul 30, 2007 at 10:40:59PM -0500, Joseph Pingenot wrote:
>> I'm trying to implement pwait.  It blocks until a specified PID exits,
>>   and then it exits.
>er... ptrace(2)?

Should work for most common usage scenarios, although will suspect that it
  won't for for processes owned by another user (at least, I hope
  it wouldn't).

What is dangerous about inotify on a proc file?

-- 
trelane@digitasaru.net.///////////////////////////////////////////////
"There is also an entire branch in the physical therapy field dedicated
 to the treatment of little-finger injuries caused by excessive Emacs
 use."  --Linux Weekly News editor (http://lwn.net/Articles/206916/)
///////260 IATL / The University of Iowa / Iowa City, IA  52242///////

Re: inotify and /proc/<pid>

[Al Viro]

On Mon, Jul 30, 2007 at 10:56:27PM -0500, Joseph Pingenot wrote:
> >From Al Viro on Tuesday, 31 July, 2007:
> >On Mon, Jul 30, 2007 at 10:40:59PM -0500, Joseph Pingenot wrote:
> >> I'm trying to implement pwait.  It blocks until a specified PID exits,
> >>   and then it exits.
> >er... ptrace(2)?
> 
> Should work for most common usage scenarios, although will suspect that it
>   won't for for processes owned by another user (at least, I hope
>   it wouldn't).
> 
> What is dangerous about inotify on a proc file?

Playing with the lifetime rules, for starters...

Re: inotify and /proc/<pid>

[Valdis.Kletnieks]

[-- Attachment #1: Type: text/plain, Size: 638 bytes --]

On Mon, 30 Jul 2007 22:56:27 CDT, Joseph Pingenot said:
> From Al Viro on Tuesday, 31 July, 2007:
> >On Mon, Jul 30, 2007 at 10:40:59PM -0500, Joseph Pingenot wrote:
> >> I'm trying to implement pwait.  It blocks until a specified PID exits,
> >>   and then it exits.
> >er... ptrace(2)?
> 
> Should work for most common usage scenarios, although will suspect that it
>   won't for for processes owned by another user (at least, I hope
>   it wouldn't).
> 
> What is dangerous about inotify on a proc file?

And if it's dangerous, should the inotify system call fail when trying to
set the watch?  Bailout with a -EBADIDEA or something?


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Re: inotify and /proc/<pid>

[Chris Friesen]

Joseph Pingenot wrote:

> While we're on the subject, is there some way to receive notification
>   that some aspect of a process changes (in this case, stopping using
>   CPU, but not exiting).

For some internal stuff a while back I did a patch that allows any 
process to register for status change notifications.  Basically, the 
registered process gets put on a list and gets the same notifications 
(killed/stopped/exited, etc.) as the real parent.

Useful for this type of thing.

Chris

Re: inotify and /proc/<pid>

[Al Viro]

On Mon, Jul 30, 2007 at 10:25:21PM -0500, Joseph Pingenot wrote:
> >From Al Viro on Tuesday, 31 July, 2007:
> >On Mon, Jul 30, 2007 at 09:16:16PM -0500, Joseph Pingenot wrote:
> >> I was trying to use inotify to watch process changes (especially process
> >>   termination) by watching /proc/<pid>.
> >> Sadly, although I could see something reading various files, nothing
> >>   was issued when the process I was watching exited and the directory
> >>   went away.
> >> Is this intentional, or a bug?
> >It's a bug you intend to introduce in your program...  IOW, don't
> >do that.
> 
> More background, please?
> 
> What's the way to check for a process exiting without spinning?

Depends on what that process is and how it is related to watching
one...

Re: inotify and /proc/<pid>

[Ray Lee]

On 7/30/07, Joseph Pingenot <trelane@digitasaru.net> wrote:
> What's the way to check for a process exiting without spinning?

I think you can get it from the taskstats interface, though I haven't
tried it. See Documentation/accounting/ for details.

Ray

Re: inotify and /proc/<pid>

[Diego Calleja]

El Mon, 30 Jul 2007 22:25:21 -0500, Joseph Pingenot <trelane@digitasaru.net> escribió:

> More background, please?
> 
> What's the way to check for a process exiting without spinning?


I don't know if it's useful for you, but CONFIG_CONNECTOR and CONFIG_PROC_EVENTS
will report process creation/exit/fork/etc through a netlink interface.

Re: inotify and /proc/<pid>

[Andrew Morton]

On Tue, 31 Jul 2007 20:31:49 +0200 Diego Calleja <diegocg@gmail.com> wrote:

> El Mon, 30 Jul 2007 22:25:21 -0500, Joseph Pingenot <trelane@digitasaru.net> escribió:
> 
> > More background, please?
> > 
> > What's the way to check for a process exiting without spinning?
> 
> 
> I don't know if it's useful for you, but CONFIG_CONNECTOR and CONFIG_PROC_EVENTS
> will report process creation/exit/fork/etc through a netlink interface.

yup.  See example code in Documentation/accounting/getdelays.c