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

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Date:	Mon, 1 Sep 2014 11:25:49 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	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()

Hi Andy,

On Mon, Sep 1, 2014 at 11:09 AM, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Mon, 2014-09-01 at 10:58 +0200, Geert Uytterhoeven wrote:
>> On Mon, Sep 1, 2014 at 10:36 AM, Andy Shevchenko
>> <andriy.shevchenko@...ux.intel.com> wrote:
>> >> ... and extra copying for no good reason.  Why not check that we have
>> >> enough space in buffer and generate directly into it?  See what e.g.
>> >> seq_escape() is doing...
>> >
>> > What about this variant?
>>
>> I think it needs a call to seq_set_overflow() in case the buffer is too small,
>> so the caller will retry with a bigger buffer.
>
> Yes, in two places it would be useful to do.

Two places? I see only one, just before calling hex_dump_to_buffer.

> But what the condition for "buffer is too small", the same groupsize * 2
> + 1 or you mean something else?

"groupsize * 2 + 1" is not the amount of bytes hex_dump_to_buffer() wants
to write. It's only the size for one word.

You could check if there are at least "32 * 3 + 2 + 32 + 1" bytes (your
old linebuf size) available.

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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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