linux-kernel - Re: [PATCH] procfs: fix the output format in /proc/PID/wchan

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Date:   Thu, 22 Nov 2018 16:38:26 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, viro@...iv.linux.org.uk,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] procfs: fix the output format in /proc/PID/wchan

On Thu, Nov 22, 2018 at 09:29:52PM +0800, Yafang Shao wrote:
> On Thu, Nov 22, 2018 at 7:40 PM Alexey Dobriyan <adobriyan@...il.com> wrote:
> >
> > On Wed, Nov 21, 2018 at 07:28:44PM -0800, Andrew Morton wrote:
> > > On Mon, 19 Nov 2018 19:17:52 +0800 Yafang Shao <laoar.shao@...il.com> wrote:
> > >
> > > > Just add the missing newline.
> > > >
> > > > ...
> > > >
> > > > --- a/fs/proc/base.c
> > > > +++ b/fs/proc/base.c
> > > > @@ -370,11 +370,12 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
> > > >     wchan = get_wchan(task);
> > > >     if (wchan && !lookup_symbol_name(wchan, symname)) {
> > > >             seq_puts(m, symname);
> > > > +           seq_putc(m, '\n');
> > > >             return 0;
> > > >     }
> > > >
> > > >  print0:
> > > > -   seq_putc(m, '0');
> > > > +   seq_puts(m, "0\n");
> > > >     return 0;
> > > >  }
> > > >  #endif /* CONFIG_KALLSYMS */
> > >
> > > What is presently wrong with the wchan output?  The changelog
> > > should explain such things, please.
> >
> > It is just newline to make "cat /proc/*/wchan" output look cool.
> > But newline can break something.
> 
> Could you pls. show some examples for what the newline may break ?

	char buf[16];
	rv = read(fd, buf, sizeof(buf));
	assert(rv == 1);