linux-kernel - Re: [PATCH v4 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs

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Message-ID: <20201103154655.GE4077@smile.fi.intel.com>
Date:   Tue, 3 Nov 2020 17:46:55 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, hverkuil@...all.nl,
        laurent.pinchart@...asonboard.com, mchehab@...nel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Perches <joe@...ches.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v4 1/1] lib/vsprintf: Add support for printing V4L2 and
 DRM fourccs

On Tue, Nov 03, 2020 at 04:56:16PM +0200, Sakari Ailus wrote:
> On Tue, Nov 03, 2020 at 04:47:47PM +0200, Andy Shevchenko wrote:
> > On Tue, Nov 03, 2020 at 03:34:00PM +0200, Sakari Ailus wrote:
> > > Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> > > pixel formats denoted by fourccs. The fourcc encoding is the same for both
> > > so the same implementation can be used.

...

> > > +	char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")];
> > 
> > I would add a comment that there is another possibility, i.e. big-endian, but
> > it occupies less space.
> 
> This string is here to represent the longest possible output of the
> function. Most of the time it's less. Saying that might make sense but it's
> fairly clear already. Either way works for me though.

It's not known by reading the above line. I would add a comment.

...

> > > +	p = special_hex_number(p, output + sizeof(output) - 2, *fourcc,
> > > +			       sizeof(u32));
> > 
> > I would go with one line here.
> 
> It's wrapped since the result would be over 80 otherwise.

It will be not the first one breaking the limit in this module for the sake of
readability.

...

> > The (theoretical) problem is here that the case when buffer size is not enough
> > to print a value will be like '(0xabc)' but should be rather '(0xabcd' like
> > snprintf() does in general.

Any comments here?
Perhaps you need to add a comment to explain that the overflow is impossible.

-- 
With Best Regards,
Andy Shevchenko