linux-kernel - Re: [PATCH] Add human-readable units modifier to vsnprintf()

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Date:	Wed, 23 May 2012 01:22:36 -0400
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Tejun Heo <tejun@...gle.com>, linux-bcache@...r.kernel.org,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com, agk@...hat.com
Subject: Re: [PATCH] Add human-readable units modifier to vsnprintf()

On Tue, May 22, 2012 at 10:10:48PM -0700, Joe Perches wrote:
> On Wed, 2012-05-23 at 00:50 -0400, Kent Overstreet wrote:
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> []
> > @@ -1002,6 +1023,7 @@ int format_decode(const char *fmt, struct printf_spec *spec)
> >  		case ' ': spec->flags |= SPACE;   break;
> >  		case '#': spec->flags |= SPECIAL; break;
> >  		case '0': spec->flags |= ZEROPAD; break;
> > +		case 'h': spec->flags |= HUNITS;  break;
> >  		default:  found = false;
> >  		}
> >  
> 
> I think that doesn't work well because
> gcc __attribute__((format(printf, x, y)))
> verification fails.

Yeah, I already ran into that. I was looking through the gcc docs to see
if there was a way to add modifiers (how is it done for the other kernel
specific format strings?) but I haven't found anything yet

> It's also possible
> to confuse it with printf's own 'h' / 
> integer precision use.

Well, that's annoying. Any suggestions?

> 
> $ cat h.c
> #include <stdio.h>
> #include <stdlib.h>
> 
> int main(int argc, char** argv)
> {
>   printf("%h02u\n", 1);
>   return 0;
> }
> 
> $ gcc h.c
> h.c: In function ‘main’:
> h.c:6:3: warning: unknown conversion type character ‘0’ in format [-Wformat]
> 
> 
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