.\" Copyright (c) 2002 Mark Santcroos <marks@ripe.net>
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.Dd November 8, 2021
.Dt NG_DEVICE 4
.Os
.Sh NAME
.Nm ng_device
.Nd device netgraph node type
.Sh SYNOPSIS
.In netgraph/ng_device.h
.Sh DESCRIPTION
A
.Nm device
node is both a netgraph node and a system device interface.
When a
.Nm device
node is created, a new device entry appears which is accessible via the
regular file operators such as
.Xr open 2 ,
.Xr close 2 ,
.Xr read 2 ,
.Xr write 2 ,
etc.
.Pp
The first node is created as
.Pa /dev/ngd0 ,
subsequent nodes are
.Pa /dev/ngd1 , /dev/ngd2 ,
etc.
.Sh HOOKS
A
.Nm device
node has a single hook with an arbitrary name.
All data coming in over the hook will be presented to the device
for
.Xr read 2 .
All data coming in from the device entry by
.Xr write 2
will be forwarded to the hook.
.Sh CONTROL MESSAGES
The
.Nm device
node supports the generic control messages, plus the following:
.Bl -tag -width 3n
.It Dv NGM_DEVICE_GET_DEVNAME
Returns the device name corresponding to the node.
.It Dv NGM_DEVICE_ETHERALIGN
Apply the system ETHER_ALIGN offset to mbufs sent out the node's hook,
if running on an architecture that requires strict alignment.
Use this option when the data being injected via the device node ultimately
ends up being fed into the protocol stack as ethernet packets (e.g., via
an
.Xr ng_eiface 4
node).
.El
.\" Additionally, the node accepts
.\" .Xr ioctl 2 Ns s
.\" from the device entry.
.\" These will be encapsulated into
.\" .Xr netgraph 4
.\" messages and send out to the hook.
.Sh SHUTDOWN
This node shuts down upon receipt of a
.Dv NGM_SHUTDOWN
control message, or upon hook disconnection.
The associated device entry is removed and becomes available
for use by future
.Nm device
nodes.
.Sh SEE ALSO
.Xr netgraph 4 ,
.Xr ngctl 8
.Sh HISTORY
The
.Nm device
node type was first implemented in
.Fx 5.0 .
.Sh AUTHORS
.An Mark Santcroos Aq Mt marks@ripe.net
.An Gleb Smirnoff Aq Mt glebius@FreeBSD.org