strerror_r questions

[Schwarz, Konrad]

> However, 
> newlib's strerror() returns "", not "Unknown error XXX", for 
> an unknown string, for three reasons:
> 1. strerror_r must be thread-safe, but it calls strerror, so 
> strerror must also be thread-safe in newlib (in general, 
> POSIX does not require strerror to be thread-safe, but in 
> that case, strerror_r cannot be implemented by calling 
> strerror); newlib achieves its thread-safety by returning 
> only constant strings (well, newlib also provides the 
> _user_sterror hook, which must be thread-safe for all this to 
> work) 2. newlib did not set aside any thread-local storage 
> for computing an alternate string, and I don't want to change 
> struct REENT to add such storage 3. newlib targets embedded 
> systems, and dragging in snprintf() to compute an alternate 
> string is bloat.

I concur: in a small embedded system, newlib's intended field
of application, strerror() should not attempt to format an
unknown error number into a string.  (just for the record)

Konrad Schwarz