* allocated buffer or map it with mmap() when available.
* In case of success set *bufptr to the read or mmapped buffer, and
* *size to the size in bytes of the buffer in *bufptr.
* allocated buffer or map it with mmap() when available.
* In case of success set *bufptr to the read or mmapped buffer, and
* *size to the size in bytes of the buffer in *bufptr.