The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/modules/netgraph/tty/ng_tty.4

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    1 .\" Copyright (c) 1996-1999 Whistle Communications, Inc.
    2 .\" All rights reserved.
    3 .\" 
    4 .\" Subject to the following obligations and disclaimer of warranty, use and
    5 .\" redistribution of this software, in source or object code forms, with or
    6 .\" without modifications are expressly permitted by Whistle Communications;
    7 .\" provided, however, that:
    8 .\" 1. Any and all reproductions of the source or object code must include the
    9 .\"    copyright notice above and the following disclaimer of warranties; and
   10 .\" 2. No rights are granted, in any manner or form, to use Whistle
   11 .\"    Communications, Inc. trademarks, including the mark "WHISTLE
   12 .\"    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
   13 .\"    such appears in the above copyright notice or in the software.
   14 .\" 
   15 .\" THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
   16 .\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
   17 .\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
   18 .\" INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
   19 .\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
   20 .\" WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
   21 .\" REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
   22 .\" SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
   23 .\" IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
   24 .\" RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
   25 .\" WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
   26 .\" PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
   27 .\" SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
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   31 .\" OF SUCH DAMAGE.
   32 .\" 
   33 .\" Author: Archie Cobbs <archie@freebsd.org>
   34 .\"
   35 .\" $FreeBSD$
   36 .\" $Whistle: ng_tty.8,v 1.5 1999/01/25 23:46:28 archie Exp $
   37 .\"
   38 .Dd January 19, 1999
   39 .Dt NG_TTY 4
   40 .Os FreeBSD
   41 .Sh NAME
   42 .Nm ng_tty
   43 .Nd netgraph node type that is also a line discipline
   44 .Sh SYNOPSIS
   45 .Fd #include <sys/ttycom.h>
   46 .Fd #include <netgraph/ng_message.h>
   47 .Fd #include <netgraph/ng_tty.h>
   48 .Sh DESCRIPTION
   49 The
   50 .Nm tty
   51 node type is both a netgraph node type and a line discipline.
   52 A new node is created when the corresponding line discipline,
   53 .Dv NETGRAPHDISC ,
   54 is registered on a tty device (see
   55 .Xr tty 4 ) .
   56 .Pp
   57 The node has a single hook called
   58 .Dv hook .
   59 Incoming bytes received on the tty device are sent out on this hook,
   60 and frames received on
   61 .Dv hook
   62 are transmitted out on the tty device.
   63 No modification to the data is performed in either direction.
   64 While the line discipline is installed on a tty, the normal
   65 read and write operations are unavailable, returning
   66 .Er EIO .
   67 .Pp
   68 The node supports an optional
   69 .Dq hot character .
   70 If set to non-zero, incoming
   71 data from the tty device is queued until this character is seen.
   72 This avoids sending lots of mbufs containing a small number of bytes,
   73 but introduces potentially infinite latency.
   74 The default hot character is 0x7e, consistent with
   75 .Dv hook
   76 being connected to a
   77 .Xr ng_async 4
   78 type node. The hot character has no effect on the transmission of data.
   79 .Pp
   80 The node will attempt to give itself the same netgraph name as the name
   81 of the tty device.
   82 In any case, information about the node is available via the netgraph
   83 .Xr ioctl 2
   84 command
   85 .Dv NGIOCGINFO .
   86 This command returns a
   87 .Dv "struct nodeinfo"
   88 similar to the
   89 .Dv NGM_NODEINFO
   90 netgraph control message.
   91 .Sh HOOKS
   92 This node type supports the following hooks:
   93 .Pp
   94 .Bl -tag -width foobar
   95 .It Dv hook
   96 .Xr tty 4
   97 serial data contained in
   98 .Dv mbuf
   99 structures, with arbitrary inter-frame boundaries.
  100 .El
  101 .Sh CONTROL MESSAGES
  102 This node type supports the generic control messages, plus the following:
  103 .Bl -tag -width foo
  104 .It Dv NGM_TTY_SET_HOTCHAR
  105 This command takes an integer argument and sets the hot character
  106 from the lower 8 bits. A hot character of zero disables queueing,
  107 so that all received data is forwarded immediately.
  108 .It Dv NGM_TTY_GET_HOTCHAR
  109 Returns an integer containing the current hot character in the lower
  110 eight bits.
  111 .Sh SHUTDOWN
  112 This node shuts down when the corresponding device is closed
  113 (or the line discipline is uninstalled on the device).
  114 The
  115 .Dv NGM_SHUTDOWN
  116 control message is not valid, and always returns the error
  117 .Er EOPNOTSUPP .
  118 .Sh BUGS
  119 The serial driver code also has a notion of a
  120 .Dq hot character .
  121 Unfortunately, this value is statically defined in terms of the
  122 line discipline and cannot be changed.
  123 Therefore, if a hot character other than 0x7e (the default) is set for the
  124 .Nm
  125 node, the node has no way to convey this information to the
  126 serial driver, and sub-optimal performance may result.
  127 .Sh SEE ALSO
  128 .Xr ioctl 2 ,
  129 .Xr netgraph 4 ,
  130 .Xr tty 4 ,
  131 .Xr ng_async 4 ,
  132 .Xr ngctl 8
  133 .Sh HISTORY
  134 The
  135 .Nm
  136 node type was implemented in
  137 .Fx 4.0 .
  138 .Sh AUTHORS
  139 .An Archie Cobbs Aq archie@freebsd.org

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