linux-kernel - Re: [RFC][PATCH 1/2] lib: printf: append support of '%*p[Mm][FR]'

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Message-ID: <CAHp75Vde4+A5NCH-YvrsrjE-KA3A+xLdMOozeFU4VV7vvUfcmQ@mail.gmail.com>
Date:	Mon, 2 Jul 2012 20:32:46 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	proski@....org, Andrei Emeltchenko <andrei.emeltchenko@...el.com>,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/2] lib: printf: append support of '%*p[Mm][FR]'

On Sat, Jun 30, 2012 at 5:48 PM, Joe Perches <joe@...ches.com> wrote:
> On Fri, 2012-06-29 at 16:26 -0700, Andrew Morton wrote:
>> On Fri, 29 Jun 2012 09:08:06 -0700
>> Joe Perches <joe@...ches.com> wrote:
>>
>> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
>> > []
>> > > @@ -655,11 +655,12 @@ char *resource_string(char *buf, char *end, struct resource *res,
>> > >  }
>> > >
>> > >  static noinline_for_stack
>> > > -char *mac_address_string(char *buf, char *end, u8 *addr,
>> > > -                  struct printf_spec spec, const char *fmt)
>> > > +char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>> > > +          const char *fmt)
>> > >  {
>> > > - char mac_addr[sizeof("xx:xx:xx:xx:xx:xx")];
>> > > - char *p = mac_addr;
>> > > + char hex_str[64*3];     /* support up to 64 bytes to print */
>> >
>> > Might be too much stack though.
>>
>> Yes, it's a bit marginal, as this new capability might be used in debug
>> or crash situations where we're deep into the stack.  The average case
>> could be improved by using alloca()-style allocation.
>
> Or maybe support larger sizes with a smaller
> stack buffer and a while loop.

What do you think about mixed approach? Let's say we would use buffer
on stack for 8 bytes or less, and allocated buffer in case of larger
input. It allows to keep implementation simple.

-- 
With Best Regards,
Andy Shevchenko
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