|NG_SOCKET(4)||Device Drivers Manual||NG_SOCKET(4)|
netgraph socket node type
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.
ng_socket node is created by
creating a new socket of type
NG_CONTROL in the
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
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
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).
This node type supports hooks with arbitrary names (as long as they are unique) and always accepts hook connection requests.
This node type supports the generic control messages, plus the following:
- When the last hook is removed from this node, it will shut down as if it
had received a
NGM_SHUTDOWNmessage. Attempts to access the sockets associated will return
- 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_GENERIC_COOKIE will be passed unaltered up the
This node type shuts down and disappears when both the associated
sockets have been closed, or a
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.
ng_socket node type was implemented in
Julian Elischer <julian@FreeBSD.org>
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).
|January 19, 1999||Debian|