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 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.
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, using
recvfrom(2); the socket address argument is a
struct sockaddr_ng
containing the sender's netgraph
address. Conversely, control messages can be sent to any node by calling
sendto(2), supplying the recipient'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
already created. Once a data socket is associated with a node, any data
packets 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 unambiguous).
There is a user library that simplifies using netgraph sockets; 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 removed,
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_CONTROL
socket.
SHUTDOWN¶
This node type shuts down and disappears when both the associated
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 also 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 node-initiated
messages should be defined for this purpose (to be sent up the control
socket).