Scroll to navigation

NG_H4(4) Device Drivers Manual NG_H4(4)


ng_h4Netgraph node type that is also an H4 line discipline


#include <sys/types.h>
#include <netgraph/bluetooth/include/ng_h4.h>


The h4 node type is both a persistent Netgraph node type and a H4 line discipline. It implements a Bluetooth HCI UART transport layer as per chapter H4 of the Bluetooth Specification Book v1.1. A new node is created when the corresponding line discipline, H4DISC, is registered on a tty device (see tty(4)).

The node has a single hook called hook. Incoming bytes received on the tty device are re-assembled into HCI frames (according to the length). Full HCI frames are sent out on the hook. HCI 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.

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(4) control message.


This node type supports the following hooks:

single HCI frame contained in single mbuf structure.


This node type supports the generic control messages, plus the following:

Reset the node.
Returns current receiving state for the node.
Returns an integer containing the current debug level for the node.
This command takes an integer argument and sets current debug level for the node.
Returns current length of outgoing queue for the node.
This command takes an integer argument and sets maximum length of outgoing queue for the node.
Returns various statistic information for the node, such as: number of bytes (frames) sent, number of bytes (frames) received and number of input (output) errors.
Reset all statistic counters to zero.


This node shuts down when the corresponding device is closed (or the line discipline is uninstalled on the device).


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


The h4 node type was implemented in FreeBSD 5.0.


Maksim Yevmenkin <>


This node still uses spltty(9) to lock tty layer. This is wrong.

June 14, 2002 Debian