Reference: Molay, Understanding Unix/Linux Programming, Chapter 5

Devices have file names

Files that represent devices are located in the /dev directory.

$ ls -C /dev | head -5
autofs           loop-control  sda7       tty19  tty39  tty59    vcsa
bsg              mapper        sda8       tty2   tty4   tty6     vcsa1
core             mqueue        sda9       tty20  tty40  tty60    vcsa2
cpu              net           sh         tty21  tty41  tty61    vcsa3
cpu_dma_latency  null          stderr     tty22  tty42  tty62    vcsa4

Devices support system calls

Devices support file-related system calls such as open, read, write, lseek, close, and stat. Unix provides no other means to communicate with devices.

Some devices can be read-only or write-only and may not support all system calls. Terminals support read and write, but not lseek

Properties of device files

Device files have most of the properties that disk files have. Device files represent connections, not data containers. The inode of a device file stores a pointer to a device driver, a subroutine in the kernel that gets data into and out of a device.

$ stat /dev/tty
  File: "/dev/tty"
  Size: 0
  FileType: Character Device
  Mode: (0666/crw-rw-rw-)
  Uid: (    0/    root)
  Gid: (    0/   wheel)
Device: 42,7610600   Inode: 303    Links: 1
Access: Wed Oct 29 11:29:57 2014
Modify: Mon Oct 20 21:03:14 2014
Change: Mon Oct 20 21:03:14 2014

File connection attributes

Disk buffering and auto-append mode can be controlled when the file connection is created using the open system call or using the fcntl system call at a later moment.

int fcntl(int fd, int cmd [, long arg | struct *flock *lockp ]);

Controls the attributes of a file descriptor fd. Operation cmd is performed with parameters arg.

Device connection attributes

Connection to a terminal has attributes setting the echo, baud rate, editing, newline conversion parameters.