The tty node type is both a netgraph node type and a line discipline. A new node is created when the corresponding line discipline, NETGRAPHDISC, is registered on a tty device (see tty(4)).
The node has a single hook called hook. Incoming bytes received on the tty device are sent out on this hook, and frames received on hook are transmitted out on the tty device. No modification to the data is performed in either direction. While the line discipline is installed on a tty, the normal read and write operations are unavailable, returning EIO.
The node supports an optional "hot character". If set to non-zero, incoming data from the tty device is queued until this character is seen. This avoids sending lots of mbufs containing a small number of bytes, but introduces potentially infinite latency. The default hot character is 0x7e, consistent with hook being connected to a ng_async(4) type node. The hot character has no effect on the transmission of data.
The node will attempt to give itself the same netgraph name as the name of the tty device. In any case, information about the node is available via the netgraph ioctl(2) command NGIOCGINFO. This command returns a "struct nodeinfo" similar to the NGM_NODEINFO netgraph control message.
This node type supports the following hooks: