0 Successful completion.
-1 Indicates an error. errno is set to one of the
following:
o EBADF - The file descriptor parameter
contains an invalid value.
o EIO - An I/O error occurred while reading
the device.
o EINTR - A signal was intercepted during
execution of the function.
o EOVERFLOW - One of the values to be
returned cannot be represented correctly
in the structure pointed to by buffer.