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

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Date:	Mon, 02 Jul 2012 14:23:19 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andy Shevchenko <andy.shevchenko@...il.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 Mon, 2012-07-02 at 20:32 +0300, Andy Shevchenko wrote:
> 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.
> 

I think the while loop is simplest.
I'll code something up tomorrow unless
you get to it first.

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