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?

>>3

they are identified as important system calls in the ANSI standard

What?

how is a thing like that changed with an unsigned return type??!

I have never seen a implementation where ssize_t is a unsigned.

Personally I never understood what is the point of ssize_t if SSIZE_MAX is less than SIZE_MAX (line in the most systems).