linux-kernel - Re: [PATCH] fs/proc: add Kthread flag to /proc/$pid/status

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Message-ID: <59774223-680e-4b64-87ea-ab7e524be369@p183>
Date:   Thu, 13 Apr 2023 21:36:58 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Chunguang Wu <aman2008@...com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/proc: add Kthread flag to /proc/$pid/status

On Wed, Apr 12, 2023 at 02:12:16PM -0700, Andrew Morton wrote:
> On Wed, 12 Apr 2023 22:34:02 +0800 Chunguang Wu <aman2008@...com> wrote:
> 
> > user can know that a process is kernel thread or not.
> > 
> > ...
> >
> > --- a/fs/proc/array.c
> > +++ b/fs/proc/array.c
> > @@ -434,6 +434,12 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
> >  
> >  	task_state(m, ns, pid, task);
> >  
> > +	if ((mm == NULL) || (task->flags & PF_KTHREAD)) {
> > +		seq_puts(m, "Kthread:\tYes\n");
> > +	} else {
> > +		seq_puts(m, "Kthread:\tNo\n");
> > +	}

"mm" check is redundant. PF_KTHREAD should be enough.
If you're doing this, just print 0/1. 

> >  	if (mm) {
> >  		task_mem(m, mm);
> >  		task_core_dumping(m, task);
> 
> Well..   Why is this information useful?

I want to add: for a shell script.
Real programs can read /proc/*/stat .

> What is the use case?
> 
> There are many ways of working this out from the existing output - why
> is this change required?