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

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Date:	Mon, 1 Sep 2014 12:59:05 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
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()

Hi Andy,

On Mon, Sep 1, 2014 at 12:15 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>>>> 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.
>
> seq_putc doesn't set it as I can see.
>
>>> 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.
>
> This is a good question why this number? What if we have to print only
> one byte (as different groupsize)?

I don't think complaining about a too-small buffer prematurely hurts.

> I think the requirement for one groupsize is quite okay.

Then you will loose data if the buffer is too small.

>> 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.

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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