ng_socket(4)

NAME

ng_socket - netgraph socket node type

SYNOPSIS

#include <sys/types.h>
#include <netgraph/ng_socket.h>

DESCRIPTION

A socket node is both a BSD socket and a netgraph node. The

ng_socket
node type allows user-mode processes to participate in the

kernel
netgraph(4) networking subsystem using the BSD socket inter

face. The
process must have root privileges to be able to create net

graph sockets
however once created, any process that has one may use it.

A new ng_socket node is created by creating a new socket of

type
NG_CONTROL in the protocol family PF_NETGRAPH, using the

socket(2) system
call. Any control messages received by the node and not

having a cookie
value of NGM_SOCKET_COOKIE are received by the process, us

ing
recvfrom(2); the socket address argument is a struct sockad

dr_ng containing the sender's netgraph address. Conversely, control mes

sages can be
sent to any node by calling sendto(2), supplying the recipi

ent's address
in a struct sockaddr_ng. The bind(2) system call may be

used to assign a
global netgraph name to the node.

To transmit and receive netgraph data packets, a NG_DATA

socket must also
be created using socket(2) and associated with a ng_socket

node. NG_DATA
sockets do not automatically have nodes associated with

them; they are
bound to a specific node via the connect(2) system call.

The address
argument is the netgraph address of the ng_socket node al

ready created.
Once a data socket is associated with a node, any data pack

ets received
by the node are read using recvfrom(2) and any packets to be

sent out
from the node are written using sendto(2). In the case of

data sockets,
the struct sockaddr_ng contains the name of the hook on

which the data
was received or should be sent.

As a special case, to allow netgraph data sockets to be used

as stdin or
stdout on naive programs, a sendto(2) with a NULL sockaddr

pointer, a
send(2) or a write(2) will succeed in the case where there

is exactly ONE
hook attached to the socket node, (and thus the path is un

ambiguous).

There is a user library that simplifies using netgraph sock

ets; see
netgraph(3).

HOOKS

This node type supports hooks with arbitrary names (as long

as they are
unique) and always accepts hook connection requests.

CONTROL MESSAGES

This node type supports the generic control messages, plus

the following:

NGM_SOCK_CMD_NOLINGER

When the last hook is removed from this node, it will

shut down as
if it had received a NGM_SHUTDOWN message. Attempts to

access the
sockets associated will return ENOTCONN.

NGM_SOCK_CMD_LINGER

This is the default mode. When the last hook is re

moved, the node
will continue to exist, ready to accept new hooks until

it is
explicitly shut down.

All other messages with neither the NGM_SOCKET_COOKIE or
NGM_GENERIC_COOKIE will be passed unaltered up the NG_CON

TROL socket.

SHUTDOWN

This node type shuts down and disappears when both the asso

ciated
NG_CONTROL and NG_DATA sockets have been closed, or a

NGM_SHUTDOWN control message is received. In the latter case, attempts to

write to the
still-open sockets will return ENOTCONN. If the

NGM_SOCK_CMD_NOLINGER
message has been received, closure of the last hook will al

so initiate a
shutdown of the node.

SEE ALSO

socket(2), netgraph(3), netgraph(4), ng_ksocket(4), ngctl(8)

HISTORY

The ng_socket node type was implemented in FreeBSD 4.0.

AUTHORS

Julian Elischer <julian@FreeBSD.org>

BUGS

It is not possible to reject the connection of a hook,

though any data
received on that hook can certainly be ignored.

The controlling process is not notified of all events that

an in-kernel
node would be notified of, e.g. a new hook, or hook removal.

Some nodeinitiated messages should be defined for this purpose (to be

sent up the
control socket).

BSD January 19, 1999

BSD