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33.\" Author: Archie Cobbs <archie@FreeBSD.org>
34.\"
35.\" $FreeBSD: src/share/man/man4/ng_tty.4,v 1.14.2.1 2001/12/21 09:00:51 ru Exp $
44cb301e 36.\" $DragonFly: src/share/man/man4/ng_tty.4,v 1.3 2006/05/26 19:39:39 swildner Exp $
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37.\" $Whistle: ng_tty.8,v 1.5 1999/01/25 23:46:28 archie Exp $
38.\"
39.Dd January 19, 1999
40.Dt NG_TTY 4
41.Os
42.Sh NAME
43.Nm ng_tty
44.Nd netgraph node type that is also a line discipline
45.Sh SYNOPSIS
46.In sys/ttycom.h
47.In netgraph/ng_message.h
44cb301e 48.In netgraph/tty/ng_tty.h
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49.Sh DESCRIPTION
50The
51.Nm tty
52node type is both a netgraph node type and a line discipline.
53A new node is created when the corresponding line discipline,
54.Dv NETGRAPHDISC ,
55is registered on a tty device (see
56.Xr tty 4 ) .
57.Pp
58The node has a single hook called
59.Dv hook .
60Incoming bytes received on the tty device are sent out on this hook,
61and frames received on
62.Dv hook
63are transmitted out on the tty device.
64No modification to the data is performed in either direction.
65While the line discipline is installed on a tty, the normal
66read and write operations are unavailable, returning
67.Er EIO .
68.Pp
69The node supports an optional
70.Dq hot character .
71If set to non-zero, incoming
72data from the tty device is queued until this character is seen.
73This avoids sending lots of mbufs containing a small number of bytes,
74but introduces potentially infinite latency.
75The default hot character is 0x7e, consistent with
76.Dv hook
77being connected to a
78.Xr ng_async 4
79type node. The hot character has no effect on the transmission of data.
80.Pp
81The node will attempt to give itself the same netgraph name as the name
82of the tty device.
83In any case, information about the node is available via the netgraph
84.Xr ioctl 2
85command
86.Dv NGIOCGINFO .
87This command returns a
88.Dv "struct nodeinfo"
89similar to the
90.Dv NGM_NODEINFO
91netgraph control message.
92.Sh HOOKS
93This node type supports the following hooks:
94.Pp
95.Bl -tag -width foobar
96.It Dv hook
97.Xr tty 4
98serial data contained in
99.Dv mbuf
100structures, with arbitrary inter-frame boundaries.
101.El
102.Sh CONTROL MESSAGES
103This node type supports the generic control messages, plus the following:
104.Bl -tag -width foo
105.It Dv NGM_TTY_SET_HOTCHAR
106This command takes an integer argument and sets the hot character
107from the lower 8 bits. A hot character of zero disables queueing,
108so that all received data is forwarded immediately.
109.It Dv NGM_TTY_GET_HOTCHAR
110Returns an integer containing the current hot character in the lower
111eight bits.
112.El
113.Sh SHUTDOWN
114This node shuts down when the corresponding device is closed
115(or the line discipline is uninstalled on the device).
116The
117.Dv NGM_SHUTDOWN
118control message is not valid, and always returns the error
119.Er EOPNOTSUPP .
120.Sh BUGS
121The serial driver code also has a notion of a
122.Dq hot character .
123Unfortunately, this value is statically defined in terms of the
124line discipline and cannot be changed.
125Therefore, if a hot character other than 0x7e (the default) is set for the
126.Nm
127node, the node has no way to convey this information to the
128serial driver, and sub-optimal performance may result.
129.Sh SEE ALSO
130.Xr ioctl 2 ,
131.Xr netgraph 4 ,
132.Xr ng_async 4 ,
133.Xr tty 4 ,
134.Xr ngctl 8
135.Sh HISTORY
136The
137.Nm
138node type was implemented in
139.Fx 4.0 .
140.Sh AUTHORS
141.An Archie Cobbs Aq archie@FreeBSD.org