linux-kernel - Re: [PATCH v2 4/4] vt: coherence validation code for the unicode screen buffer

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Date:   Tue, 19 Jun 2018 08:14:57 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Joe Perches <joe@...ches.com>
cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Mielke <Dave@...lke.cc>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] vt: coherence validation code for the unicode
 screen buffer

On Mon, 18 Jun 2018, Joe Perches wrote:

> On Mon, 2018-06-18 at 21:50 -0400, Nicolas Pitre wrote:
> > On Tue, 19 Jun 2018, Andy Shevchenko wrote:
> []
> > > > +       /*
> > > > +        * Make sure our unicode screen translates into the same glyphs
> > > > +        * as the actual screen. This is brutal indeed.
> > > > +        */
> > > > +       p = (unsigned short *)vc->vc_origin;
> > > > +       mask = vc->vc_hi_font_mask | 0xff;
> > > > +       for (y = 0; y < vc->vc_rows; y++) {
> > > > +               char32_t *line = uniscr->lines[y];
> > > > +               for (x = 0; x < vc->vc_cols; x++) {
> > > > +                       u16 glyph = scr_readw(p++) & mask;
> > > > +                       char32_t uc = line[x];
> > > > +                       int tc = conv_uni_to_pc(vc, uc);
> > > > +                       if (tc == -4)
> > > > +                               tc = conv_uni_to_pc(vc, 0xfffd);
> > > > +                       if (tc == -4)
> > > > +                               tc = conv_uni_to_pc(vc, '?');
> > > > +                       if (tc != glyph)
> > > > +                               pr_notice("%s: mismatch at %d,%d: "
> > > > +                                         "glyph=%#x tc=%#x\n", __func__,
> > > > +                                         x, y, glyph, tc);
> > > 
> > > Don't split format string in printk(). checkpatch will not warn on longer lines.
> > 
> > I didn't do it like that for checkpatch but to keep the code readable.
> > I don't particularly care either ways though.
> 
> If one glyph is off, then perhaps others are off too.
> Perhaps this message should be ratelimited.

Remember that this is costly debugging code that is off by default. 
No production kernel should have it enabled.


Nicolas