linux-kernel - Re: [RFC][PATCH 04/12 v3] tracing: Convert seq_buf_path() to be like seq

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Date:	Wed, 5 Nov 2014 15:10:53 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 04/12 v3] tracing: Convert seq_buf_path() to be
 like seq_path()

On Wed, 5 Nov 2014 15:45:53 +0100
Petr Mladek <pmladek@...e.cz> wrote:


> >   */
> > -int seq_buf_path(struct seq_buf *s, const struct path *path)
> > +int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
> >  {
> > -	unsigned int len = SEQ_BUF_LEFT(s);
> > -	unsigned char *p;
> > -
> > -	WARN_ON(s->size == 0);
> 
> I would keep this check.

Yeah, I could.

> 
> > -	p = d_path(path, s->buffer + s->len, len);
> > -	if (!IS_ERR(p)) {
> > -		p = mangle_path(s->buffer + s->len, p, "\n");
> > -		if (p) {
> > -			s->len = p - s->buffer;
> > -			return 0;
> > +	char *buf = s->buffer + s->len;
> > +	size_t size = SEQ_BUF_LEFT(s);
> 
> I would use the variable name "len" to make it consistent with
> the other fucntions in seq_buf.c.

Note, seq_path() is a different beast than the other seq_*() functions
(this will be keeping a return code). And the inconsistency is in
seq_file.c as well. I'm not saying we shouldn't keep it consistent. But
as this patch is to make seq_buf like seq_file, I'll keep the
inconsistencies the same too.

We can always do a clean up later.


> 
> > +	int res = -1;
> > +
> > +	if (size) {
> > +		char *p = d_path(path, buf, size);
> > +		if (!IS_ERR(p)) {
> > +			char *end = mangle_path(buf, p, esc);
> > +			if (end)
> > +				res = end - buf;
> >  		}
> >  	}
> > -	seq_buf_set_overflow(s);
> 
> We still should set overflow on failure.

Again, this is different in seq_file too. I'm leaving it as is.

> 
> > -	return -1;
> > +	if (res > 0)
> > +		s->len += res;
> > +
> > +	return res;
> 
> It returns -1 on failure and the number of written characters on
> success. This is incompatible with the other seq_buf functions
> and with the comment above this function. Also it changes the
> return value from trace_seq_path().
> 
> I do not mind about the used scheme but I think that we should
> make it consistent.
> 

As seq_file has had this inconsistency for a long time, and this code
is to try to merge the code between trace_seq and seq_file, I'm going
to follow seq_file as that has been around much longer than trace_seq.

-- Steve

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