ng_tty(4)

NAME

ng_tty - netgraph node type that is also a line discipline

SYNOPSIS

#include <sys/types.h>
#include <sys/ttycom.h>
#include <netgraph/ng_tty.h>

DESCRIPTION

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 re

ceived 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 char

acter 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.

HOOKS

This node type supports the following hooks:

hook tty(4) serial data contained in mbuf structures,

with arbitrary

inter-frame boundaries.

CONTROL MESSAGES

This node type supports the generic control messages, plus

the following:

NGM_TTY_SET_HOTCHAR

This command takes an integer argument and sets the hot

character
from the lower 8 bits. A hot character of zero dis

ables queueing,
so that all received data is forwarded immediately.

NGM_TTY_GET_HOTCHAR

Returns an integer containing the current hot character

in the lower
eight bits.

SHUTDOWN

This node shuts down when the corresponding device is closed

(or the line
discipline is uninstalled on the device). The NGM_SHUTDOWN

control message is not valid, and always returns the error EOPNOTSUPP.

SEE ALSO

ioctl(2), netgraph(4), ng_async(4), tty(4), ngctl(8)

HISTORY

The ng_tty node type was implemented in FreeBSD 4.0.

AUTHORS

Archie Cobbs <archie@FreeBSD.org>

BUGS

The serial driver code also has a notion of a ``hot charac

ter''. Unfortunately, this value is statically defined in terms of the

line discipline and cannot be changed. Therefore, if a hot character

other than
0x7e (the default) is set for the ng_tty node, the node has

no way to
convey this information to the serial driver, and sub-opti

mal performance
may result.

BSD January 19, 1999

BSD