File or memory access pattern advisory information.
A descriptor is a reference to a filesystem object, which may be a file,
directory, named pipe, special file, or other object on which filesystem
calls may be made.
The type of a filesystem object referenced by a descriptor.
Error codes returned by functions, similar to errno
in POSIX.
Not all of these error codes are returned by the functions provided by this
API; some are used in higher-level library layers, and others are provided
merely for alignment with POSIX.
When setting a timestamp, this gives the value to set it to.