linux-kernel - Re: [PATCH v2] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf

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Date:   Thu, 26 Oct 2023 16:33:17 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@....de>,
        Justin Stitt <justinstitt@...gle.com>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Petr Mladek <pmladek@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Yun Zhou <yun.zhou@...driver.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        linux-trace-kernel@...r.kernel.org,
        Yosry Ahmed <yosryahmed@...gle.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_str()

On Thu, 26 Oct 2023 23:20:15 +0300
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> > +#define DECLARE_SEQ_BUF(NAME, SIZE)					\
> > +	char __ ## NAME ## _buffer[SIZE] = "";				\
> > +	struct seq_buf NAME = { .buffer = &__ ## NAME ## _buffer,	\
> > +				.size = SIZE }  
> 
> Hmm... Wouldn't be more readable to have it as
> 
> #define DECLARE_SEQ_BUF(NAME, SIZE)			\
> 	char __ ## NAME ## _buffer[SIZE] = "";		\
> 	struct seq_buf NAME = {				\
> 		.buffer = &__ ## NAME ## _buffer,	\
> 		.size = SIZE,				\
> 	}
> 
> ?

I agree with the above.

> 
> ...
> 
> > +static inline char *seq_buf_str(struct seq_buf *s)
> >  {
> >  	if (WARN_ON(s->size == 0))
> > -		return;
> > +		return "";  
> 
> I'm wondering why it's a problem to have an empty string?

Not sure what you mean? With s->size = 0, s->buffer may not have been
assigned. That shouldn't be the case, but it does make it more robust.

-- Steve


> 
> >  	if (seq_buf_buffer_left(s))
> >  		s->buffer[s->len] = 0;
> >  	else
> >  		s->buffer[s->size - 1] = 0;
> > +
> > +	return s->buffer;
> >  }  
>