C over the years

Does anyone know why did the definitions of many functions in the C standard library got changed to return ssize_t instead of int? For instance read and write, both returning -1 in case of error, whilst all declarations of ssize_t I've seen are unsigned. What is this crazyness?

>>13
On linux every target architecture with 64bit addresses have long and long long the same size, 64 bits. Anyways you have fixed length integer types in the C99 standard, the same standard that introduced long longs.