linux-kernel - Re: [PATCH] staging: lustre: lustre: libcfs: debug.c: Cleaning up unnecessary use of memset in conjunction with strncpy

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Date:	Thu, 18 Sep 2014 00:12:42 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peng Tao <bergwolf@...il.com>, devel@...verdev.osuosl.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: lustre: lustre: libcfs: debug.c: Cleaning up
 unnecessary use of memset in conjunction with strncpy

2014-09-15 10:23 GMT+02:00 Dan Carpenter <dan.carpenter@...cle.com>:
> On Sun, Sep 14, 2014 at 06:03:16PM +0200, Rickard Strandqvist wrote:
>> Using memset before strncpy just to ensure a trailing null
>> character is an unnecessary double writing of a string
>>
>
> You really should make a function which pads and NUL terminates.
>
> I've said this before, of course, but you haven't even tried.
>
> I can't get excited about these cleanups which open code NUL termination
> every where.  They are risky and have introduced bugs before.
>
> regards,
> dan carpenter



Hi Dan

Ok, I have made two suggestions for strncpy function that also
guarantees a terminating null character.
1) retunerar number of characters to be copied, it can be good to
have, but was not really satisfied.

int strncpyz(char *dest, const char *src, size_t count)
{
  size_t len=0;

  if(0 == count)
    return 0;

  --count;
  while(len < count && src[len])
   *dest++ = src[len++];

  do {
    *dest++ = '\0';
  }
  while(len < count--);

  return len;
}


2) The next version is almost the same code as the regular strncpy,
but with two extra lines.

char *strncpyz(char *dest, const char *src, size_t count)
{
        char *tmp = dest;

        while (count) {
                if ((*tmp = *src) != 0)
                        src++;
                tmp++;
                count--;
        }

        if(tmp != dest)
          *--tmp = '\0';

        return dest;
}


Since I did not got any better solution to variant 1, I prefer variant 2.

Then the next question is of course what it should be called  :-)


Kind regards
Rickard Strandqvist
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