Re: [patch 1/4] fs, proc: Introduce /proc/<pid>/task/<tid>/childrenentry v8

[KAMEZAWA Hiroyuki]

On Tue, 24 Jan 2012 10:53:38 +0400
Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:

> On Tue, Jan 24, 2012 at 11:07:30AM +0900, KAMEZAWA Hiroyuki wrote:
> ...
> > 
> > From viewpoint I played with seq_file, yesterday.
> > 
> > > +static void *children_seq_start(struct seq_file *seq, loff_t *pos)
> > > +{
> > > +	return get_children_pid(seq->private, NULL, *pos);
> > > +}
> > > +
> > > +static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> > > +{
> > > +	struct pid *pid = NULL;
> > > +
> > > +	pid = get_children_pid(seq->private, v, *pos + 1);
> > > +	if (!pid)
> > > +		seq_printf(seq, "\n");
> > > +	put_pid(v);
> > 
> > Because seq_printf() may fail. This seems dangeorus.
> > 
> > If seq_printf() fails and returns NULL, "\n" will not be
> > printed out and user land parser will go wrong.
> >
> 
> Hmm. But userspace app will get eof, so frankly I don't see
> a problem here. Or maybe I miss something?
> 

Userspace need to take care of whether there may be"\n" or not even
if read() returns EOF.
As an interface, it's BUG to say "\n" will be there if you're lucky!"
(*) I know script language can handle this but we shouldn't assume that.

How about just remove "\n" at EOF  ? I think it's unnecessary.

Thanks,
-Kame


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/