Master Driver and Slave Driver Characteristics

The master driver and slave driver have the following characteristics:

• Each master driver has one-to-one relationship with a slave device based on major/minor device numbers.

• Only one open is allowed on a master device. Multiple opens are allowed on the slave device according to standard file mode and ownership permissions.

• Each slave driver minor device has a node in the file system.

• An open on a master device automatically locks out an open on the corresponding slave driver.

• A slave cannot be opened unless the corresponding master is open and has unlocked the slave.

• To provide a TTY interface to the user, the ldterm and ptem modules are pushed on the slave side.

• A close on the master sends a hang up to the slave and renders both streams unusable, after all data have been consumed by the process on the slave side.

• The last close on the slave side sends a zero-length message to the master but does not sever the connection between the master and slave drivers.