OS specific implimentations of WriteAt and/or ReadAt
Use an offset as the base for all ReadAt and WriteAt accesses. Where
Limit the amount of data accepted in a single call to WriteAt (ReadAt is unaffected)
Adapt a WriteAt and/or ReadAt to a Write and/or Read by tracking a single internal offset and modifying it.
Allow a Seek + (Read and/or Write) to impliment WriteAt and/or ReadAt
Limit the maximum offset of a WriteAt and/or ReadAt.
Read data at an offset
Write data at an offset