linux-kernel - Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs

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Message-ID: <e44e41317719727ea12aee4ff1e210dea796dd2f.camel@perches.com>
Date:   Fri, 03 Apr 2020 11:38:29 -0700
From:   Joe Perches <joe@...ches.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-media@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        hverkuil@...all.nl, mchehab@...nel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH v2 1/1] lib/vsprintf: Add support for printing V4L2 and
 DRM fourccs

On Fri, 2020-04-03 at 13:47 +0300, Sakari Ailus wrote:
> On Fri, Apr 03, 2020 at 01:24:49PM +0300, Laurent Pinchart wrote:
> > On Fri, Apr 03, 2020 at 12:11:56PM +0300, Sakari Ailus wrote:
> > > Add a printk modifier %ppf (for pixel format) for printing V4L2 and DRM
> > > pixel formats denoted by 4ccs. The 4cc encoding is the same for both so
> > > the same implementation can be used.
[]
> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> > > +static noinline_for_stack
> > > +char *fourcc_string(char *buf, char *end, const u32 *fourcc,
> > > +		    struct printf_spec spec, const char *fmt)
[]
> > > +	if (fmt[1] != 'c' || fmt[2] != 'c')

This could check outside a format string if
the %p4 is at the end of the format string.

	printk("%p4", fourcc)

So this should verify

	if (!(fmt[1] == 'c' && fmt[2] == 'c'))