linux-kernel - Re: [RFC][PATCH 07/12 v3] tracing: Have seq

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Date:	Wed, 5 Nov 2014 15:21:30 -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 07/12 v3] tracing: Have seq_buf use full buffer

On Wed, 5 Nov 2014 17:31:50 +0100
Petr Mladek <pmladek@...e.cz> wrote:


> >  /**
> >   * seq_buf_print_seq - move the contents of seq_buf into a seq_file
> > @@ -55,7 +55,7 @@ int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args)
> >  
> >  	if (s->len < s->size) {
> >  		len = vsnprintf(s->buffer + s->len, s->size - s->len, fmt, args);
> > -		if (s->len + len < s->size) {
> > +		if (s->len + len <= s->size) {
> 
> This is always true because we limit vsnprintf() to write (s->size -
> s->len) bytes. Similar problem is also in the other parts of this
> patch.

No, len is the length of bytes that should have been written, not the
amount that has been written.

> 
> I wonder if we want this change at all. It means that we are not able to
> detect overflow in some functions. It is pity because the users
> might want to increase the buffer size and try again if the print
> was incomplete.

What do you mean we can't detect overflow? That's what
seq_buf_has_overflowed() does.

> 
> I think that we need to leave the one byte for the overflow detection
> if we want to detect it properly.

I don't.

-- Steve
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