Change the properties of the open file fid. The following values may be passed as request:
F_DUPFD- Return a duplicate file descriptor.
F_GETFD- Return the file descriptor flags for fid.
F_SETFD- Set the file descriptor flags for fid.
F_GETFL- Return the file status flags for fid. The following codes may be returned (some of the flags may be undefined on some systems).
O_RDONLY- Open for reading only.
O_WRONLY- Open for writing only.
O_RDWR- Open for reading and writing.
O_APPEND- Append on each write.
O_CREAT- Create the file if it does not exist.
O_NONBLOCK- Nonblocking mode.
O_SYNC- Wait for writes to complete.
O_ASYNC- Asynchronous I/O.
F_SETFL- Set the file status flags for fid to the value specified by arg. The only flags that can be changed are
O_APPENDandO_NONBLOCK.If successful, err is 0 and msg is an empty string. Otherwise, err is nonzero and msg contains a system-dependent error message.