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

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Date:   Fri, 23 Nov 2018 17:57:23 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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 9:38 PM Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> 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);

That's really a break, so we can't apply this patch.

Hi Andrew,
I found that you have applied this patch to -mm tree, could you pls.
help revert it as it may break something ?

Thanks
Yafang