strerror_r questions

Eric Blake
Thu Feb 10 00:17:00 GMT 2011

On 02/09/2011 03:43 PM, Eric Blake wrote:
>>> -  return strncpy (buffer, (const char *)error, n);
>>> +  strncpy (buffer, error, n);
>>> +  return strlen (error) >= n ? error : buffer;
>> This looks wrong to me.  Glibc guarantees that the copied result in
>> buffer is NUL-terminated, and I'm missing the "Unknown error XXX"
>> message.
> No.  I strongly feel that strerror and strerror_r should return the same
> strings (insofar as possible).

Oh, and I just re-read the glibc man page:

       The GNU-specific strerror_r() returns a pointer to a string
       the  error  message.  This may be either a pointer to a string
that the
       function stores in buf, or a pointer to some (immutable) static
       (in which case buf is unused).  If the function stores a string
in buf,
       then at most buflen bytes are stored (the string may  be
truncated  if
       buflen  is too small) and the string always includes a
terminating null

That is, my implementation was wrong, and buf should be left untouched
if it is not the return value.  Will fix in v2.

Eric Blake    +1-801-349-2682
Libvirt virtualization library

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