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NG_TTY(4)		 BSD 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 de-
     liver 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 in-
	   ter-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".  Unfortu-
     nately, 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-optimal performance	may
     result.

BSD			       December	25, 2008			   BSD

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

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