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NG_TTY(4)	       FreeBSD Kernel Interfaces Manual		     NG_TTY(4)

NAME
     ng_tty -- netgraph	node type that is also a TTY hook

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 TTY hook.

     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	per-
     formed in either direction.  While	the hook is installed on a tty,	the
     normal read and write operations are unavailable, returning EIO.

     Incoming data is delivered	directly to ng_tty via the tty bypass hook as
     a buffer pointer and length, this is converted to a mbuf and passed to
     the peer.

     The node supports an optional ``hot character''.  If the driver can not
     deliver data directly to the tty bypass hook then each character is input
     one at a time.  If	set to non-zero	and bypass mode	is unavailable,	incom-
     ing 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.

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 disables 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.

     NGM_TTY_SET_TTY
	  This command takes integer process ID	and file descriptor of open
	  tty and registers the	tty hooks.

SHUTDOWN
     This node shuts down when the corresponding device	is closed.

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>
     Andrew Thompson <thompsa@FreeBSD.org>

BUGS
     The serial	driver code also has a notion of a ``hot character''.  Unfor-
     tunately, this value is statically	defined	in terms of the	line disci-
     pline 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-optimal performance
     may result.

FreeBSD	10.1		       December	25, 2008		  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | HOOKS | CONTROL MESSAGES | SHUTDOWN | SEE ALSO | HISTORY | AUTHORS | BUGS

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