linux-kernel - Re: [PATCH v3 1/5] seq_file: provide an analogue of print_hex

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Date:	Mon, 1 Sep 2014 14:53:16 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Tadeusz Struk <tadeusz.struk@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Helge Deller <deller@....de>,
	Ingo Tuchscherer <ingo.tuchscherer@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Joe Perches <joe@...ches.com>, Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v3 1/5] seq_file: provide an analogue of print_hex_dump()

On Mon, Sep 1, 2014 at 2:49 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Andy,
>
> On Mon, Sep 1, 2014 at 1:33 PM, Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
>>> >> However, to protect against overflows if hex_dump_to_buffer() ever changes,
>>> >> I think it would be better to let hex_dump_to_buffer() indicate if the
>>> >> passed buffer was to small (it already checks the passed linebuflen).
>>> >> Then you can just check for that.
>>> >
>>> > I thought about that. We may introduce either new call and make
>>> > current one the user of it or change all occurrences.
>>> > Nevertheless, currently it will print only one groupsize if there is
>>> > enough room for it but for two or more.
>>> > Thus, I prefer to keep the behaviour "print until we can".
>>>
>>> The idea of seq_*() is that it will retry with a bigger bufsize if there's
>>> not enough space.
>>
>> Fair enough.
>>
>> So, summarize above, the check before hex_dump_to_buffer() should care
>> about maximum possible buffer needed for one line. But we have already
>> rowsize calculated (we actually can't rely on groupsize in this case).
>>
>> Do you agree with formula rowsize * 3 + 2 + rowsize + 1?
>
> That's the _current_ formula. The day hex_dump_to_buffer() is changed,
> it will break silently.

Do we have any other option except modify hex_dump_to_buffer() to
return an error when buffer is not enough?
In this case we require hex_dump_to_buffer() to follow this agreement
even if it's changed once.

-- 
With Best Regards,
Andy Shevchenko
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