linux-kernel - Re: [PATCH 1/5] lib: string.c: Added a function strzcpy

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Date:	Sun, 19 Oct 2014 08:05:34 -0700
From:	Joe Perches <joe@...ches.com>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] lib: string.c: Added a function strzcpy

On Sun, 2014-10-19 at 14:19 +0200, Rickard Strandqvist wrote:
> 2014-10-19 3:38 GMT+02:00 Joe Perches <joe@...ches.com>:
> > On Sun, 2014-10-19 at 00:03 +0200, Rickard Strandqvist wrote:
> >> Added a function strzcpy which works the same as strncpy,
> >> but guaranteed to produce the trailing null character.
> >>
> >> There are many places in the code where strncpy used although it
> >> must be zero terminated, and switching to strlcpy is not an option
> >> because the string must nonetheless be fyld with zero characters.
> > []
> >> diff --git a/lib/string.c b/lib/string.c
> > []
> >> +char *strzcpy(char *dest, const char *src, size_t count)
> >> +{
> >> +     char *tmp = dest;
> >> +
> >> +     while (count) {
> >> +             if ((*tmp = *src) != 0)
> >> +                     src++;
> >> +             tmp++;
> >> +             count--;
> >> +     }
> >> +
> >> +     if (dest != tmp)
> >> +             *--tmp = '\0';
> >> +
> >> +     return dest;
> >> +}
> >
> > why not
> >
> > char *strzcpy(char *dest, const char *src, size_t count)
> > {
> >         strncpy(dest, src, count)
> >         if (count)
> >                 dest[count - 1] = 0; /* or '\0' or whatever */
> >
> >         return dest;
> > }
> >
> > maybe use static inline too.
> >
> 
> Hi Joe
> 
> Yes this solution have also been discussed.
> https://lkml.org/lkml/2014/10/16/682
> 
> Very possible that it is a better solution.
> The code that I use in strzcpy is not the way I'd written it, but is
> the same as in strncpy now.
> 
> But as I understand it the real strncpy code is normally highly
> optimized for the hardware it runs on.
> Ex: arch/x86/lib/string_32.c

The fact that optimized strncpy variants exist
for any platform is the argument _for_ using it
in strzcpy.

> But missing for x86 64 bit and Arm..?



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