Re: [PATCH] strerror_r: enforce POSIX recommendations

[Bruno Haible]

Eric Blake wrote:
>  2011-05-20  Eric Blake  <address@hidden>
> 
> +     strerror_r: enforce POSIX recommendations
> +     * lib/strerror_r.c (safe_copy): New helper method.
> +     (strerror_r): Guarantee a non-empty string.
> +     * tests/test-strerror_r.c (main): Enhance tests to incorporate
> +     recent POSIX rulings and to match our strerror guarantees.
> +     * doc/posix-functions/strerror_r.texi (strerror_r): Document this.

This looks good, except one part:

> @@ -436,9 +448,16 @@ strerror_r (int errnum, char *buf, size_t buflen)
>      {
>        extern int __xpg_strerror_r (int errnum, char *buf, size_t buflen);
> 
> +      *buf = '\0';
>        ret = __xpg_strerror_r (errnum, buf, buflen);
>        if (ret < 0)
>          ret = errno;
> +      if (!*buf)
> +        {
> +          /* GNU strerror_r always returns a thread-safe untruncated
> +             string; copy that into our buf.  */
> +          safe_copy (buf, buflen, strerror_r (errnum, buf, buflen));
> +        }
>      }

Here I would prefer to use __xpg_strerror_r a second time, with a
stack-allocated buffer of size 256. This is simpler than to use two
different functions from the system. Also "GNU strerror_r always returns
a thread-safe untruncated string" is an assumption, and if we can write
code that makes less assumptions, it's better.

Bruno
-- 
In memoriam Alfred Grünberg <http://en.wikipedia.org/wiki/Alfred_Grünberg>