freebsd-dev/share/man/man4/ng_socket.4

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.\" Author: Archie Cobbs <archie@FreeBSD.org>
.\"
.\" $FreeBSD$
.\" $Whistle: ng_socket.8,v 1.5 1999/01/25 23:46:27 archie Exp $
.\"
.Dd January 19, 1999
.Dt NG_SOCKET 4
.Os
.Sh NAME
.Nm ng_socket
.Nd netgraph socket node type
.Sh SYNOPSIS
.In netgraph/ng_message.h
.In netgraph/ng_socket.h
.Sh DESCRIPTION
A
.Nm socket
node is both a
.Bx
socket and a netgraph node.  The
.Nm
node type allows user-mode processes to participate in the kernel
.Xr netgraph 4
networking subsystem using the
.Bx
socket interface. The process must have
root privileges to be able to create netgraph sockets however once created,
any process that has one may use it.
.Pp
A new
.Nm
node is created by creating a new socket of type
.Dv NG_CONTROL
in the protocol family
.Dv PF_NETGRAPH ,
using the
.Xr socket 2
system call.
Any control messages received by the node
and not having a cookie value of
.Dv NGM_SOCKET_COOKIE
are received  by the process, using
.Xr recvfrom 2 ;
the socket address argument is a
.Dv "struct sockaddr_ng"
containing the sender's netgraph address. Conversely, control messages
can be sent to any node by calling
.Xr sendto 2 ,
supplying the recipient's address in a
.Dv "struct sockaddr_ng" .
The
.Xr bind 2
system call may be used to assign a global netgraph name to the node.
.Pp
To transmit and receive netgraph data packets, a
.Dv NG_DATA
socket must also be created using
.Xr socket 2
and associated with a
.Nm
node.
.Dv NG_DATA sockets do not automatically
have nodes associated with them; they are bound to a specific node via the
.Xr connect 2
system call. The address argument is the netgraph address of the
.Nm
node already created. Once a data socket is associated with a node,
any data packets received by the node are read using
.Xr recvfrom 2
and any packets to be sent out from the node are written using
.Xr sendto 2 .
In the case of data sockets, the
.Dv "struct sockaddr_ng"
contains the name of the
.Em hook
on which the data was received or should be sent.
.Pp
As a special case, to allow netgraph data sockets to be used as stdin or stdout
on naive programs, a
.Xr sendto  2
with a NULL sockaddr pointer, a
.Xr send 2
or a
.Xr write 2
will succeed in the case where there is exactly ONE hook  attached to
the socket node, (and thus the path is unambiguous).
.Pp
There is a user library that simplifies using netgraph sockets; see
.Xr netgraph 3 .
.Sh HOOKS
This node type supports hooks with arbitrary names (as long as
they are unique) and always accepts hook connection requests.
.Sh CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
.Bl -tag -width foo
.It Dv NGM_SOCK_CMD_NOLINGER
When the last hook is removed from this node, it will shut down as
if it had received a
.Dv NGM_SHUTDOWN
message. Attempts to access the sockets associated will return
.Er ENOTCONN .
.It Dv NGM_SOCK_CMD_LINGER
This is the default mode. When the last hook is removed, the node will
continue to exist, ready to accept new hooks until it
is explicitly shut down.
.El
.Pp
All other messages
with neither the
.Dv NGM_SOCKET_COOKIE
or
.Dv NGM_GENERIC_COOKIE
will be passed unaltered up the
.Dv NG_CONTROL
socket.
.Sh SHUTDOWN
This node type shuts down and disappears when both the associated
.Dv NG_CONTROL
and
.Dv NG_DATA
sockets have been closed, or a
.Dv NGM_SHUTDOWN
control message is received. In the latter case, attempts to write
to the still-open sockets will return
.Er ENOTCONN .
If the
.Dv NGM_SOCK_CMD_NOLINGER
message has been received, closure of the last hook will also initiate
a shutdown of the node.
.Sh BUGS
It is not possible to reject the connection of a hook, though any
data received on that hook can certainly be ignored.
.Pp
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. We should define
some node-initiated messages for this purpose (to be sent up the control
socket).
.Sh SEE ALSO
.Xr socket 2 ,
.Xr netgraph 3 ,
.Xr netgraph 4 ,
.Xr ng_ksocket 4 ,
.Xr ngctl 8
.Sh HISTORY
The
.Nm
node type was implemented in
.Fx 4.0 .
.Sh AUTHORS
.An Julian Elischer Aq julian@FreeBSD.org