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

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Date:	Sun, 19 Oct 2014 14:19:57 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Joe Perches <joe@...ches.com>
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

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

But missing for x86 64 bit and Arm..?


Kind regards
Rickard Strandqvist
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