linux-kernel - Re: [RFC PATCH v1 6/6] tools/include/string: Implement `strdup()` and `strndup()`

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Date:   Mon, 21 Mar 2022 09:51:00 +0100
From:   Willy Tarreau <w@....eu>
To:     Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>
Cc:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nugraha <richiisei@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>
Subject: Re: [RFC PATCH v1 6/6] tools/include/string: Implement `strdup()`
 and `strndup()`

On Mon, Mar 21, 2022 at 03:16:54PM +0700, Alviro Iskandar Setiawan wrote:
> On Mon, Mar 21, 2022 at 2:53 PM Willy Tarreau wrote:
> > Here it can cost quite a lot for large values of maxlen. Please just use
> > a variant of the proposal above like this one:
> >
> >         size_t len;
> >         char *ret;
> >
> >         len = strlen(str);
> >         if (len > maxlen)
> >                 len = maxlen;
> >         ret = malloc(len + 1);
> >         if (ret)
> >                 memcpy(ret, str, len);
> >         return ret;
> 
> Maybe better to use strnlen(), see the detail at man 3 strnlen.
> 
>   size_t strnlen(const char *s, size_t maxlen);
> 
> The strnlen() function returns the number of bytes in the string
> pointed to by s, excluding the terminating null byte ('\0'), but at
> most maxlen. In doing this, strnlen() looks only at the first maxlen
> characters in the string pointed to by s and never beyond s[maxlen-1].
> 
> Should be trivial to add strnlen() with a separate patch before this patch.
> 
> So it can be:
> 
>     size_t len;
>     char *ret;
> 
>     len = strnlen(str, maxlen);
>     ret = malloc(len + 1);
>     if (__builtin_expect(ret != NULL, 1)) {
>         memcpy(ret, str, len);
>         ret[len] = '\0';
>     }
>     return ret;
> 
> Thoughts?

I thought about it as well and while I was seeking the simplest route,
I agree it would indeed be cleaner.

Willy