linux-kernel - Re: [PATCH v4 02/28] printk: Add print format (%pra) for struct range

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Message-ID: <ZwaWJcfD8lPLhpY2@black.fi.intel.com>
Date: Wed, 9 Oct 2024 17:41:41 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Ira Weiny <ira.weiny@...el.com>, Dave Jiang <dave.jiang@...el.com>,
	Fan Ni <fan.ni@...sung.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Navneet Singh <navneet.singh@...el.com>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	linux-btrfs@...r.kernel.org, linux-cxl@...r.kernel.org,
	linux-doc@...r.kernel.org, nvdimm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v4 02/28] printk: Add print format (%pra) for struct range

On Wed, Oct 09, 2024 at 03:30:14PM +0200, Rasmus Villemoes wrote:

...

> Rather than the struct assignments, I think it's easier to read if you
> just do
> 
>   struct range r;
> 
>   r.start = 0xc0ffee00ba5eba11;
>   r.end   = r.start;
>   ...
> 
>   r.start = 0xc0ffee;
>   r.end   = 0xba5eba11;
>   ...
> 
> which saves two lines per test and for the first one makes it more
> obvious that the start and end values are identical.

With DEFINE_RANGE() it will save even more lines!

..

> > +		if (buf < end)
> > +			*buf++ = '-';
> 
> No. Either all your callers pass a (probably stack-allocated) buffer
> which is guaranteed to be big enough, in which case you don't need the
> "if (buf < end)", or if some callers may "print" directly to the buffer
> passed to vsnprintf(), the buf++ must still be done unconditionally in
> order that vsnprintf(NULL, 0, ...) [used by fx kasprintf] can accurately
> determine how large the output string would be.

Ah, good catch, I would add...

> So, either
> 
>   *buf++ = '-'
> 
> or
> 
>   if (buf < end)
>     *buf = '-';
>   buf++;

...that we use rather ++buf in such cases, but it doesn't really matter.

> Please don't mix the two. 

-- 
With Best Regards,
Andy Shevchenko