Constant SYS_FCNTL 

pub const SYS_FCNTL: usize = 316; // 316usize

File control operations (fcntl).

• fd: file descriptor
• cmd: command (F_DUPFD, F_GETFD, F_SETFD, F_GETFL, F_SETFL)
• arg: command-specific argument

Returns a command-dependent value.