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4.1.3 Netlink Connections

The (netlink connection) module defines the following procedures, used to connect and communicate with another process or the kernel using a netlink socket.

Scheme Procedure: get-addr family pid groups ¶

Return a bytevector that represents a netlink address. family should be AF_NETLINK, pid is the PID of the process with which to communicate or 0 for the kernel. groups is an integer representing the set of broadcast groups to which the connection subscribes.

Scheme Procedure: connect proto addr [#:flags 0] ¶

Creates a netlink socket for proto and binds it to addr.

proto is the integer representing the protocol. For instance, rtnetlink can be selected by usin NETLINK_ROUTE (defined in (netlink constant)).

addr is a bytevector, as returned by get-addr.

flags is a set of additional flags to pass as the second argument to the socket system call—e.g., SOCK_NONBLOCK.

Scheme Procedure: connect-route [#:groups 0] [#:flags 0] ¶

This procedure is a wrapper for connect that creates a socket for the rtnetlink protocol, binds it to the kernel and returns it. By passing the optional groups keyword, you can select broadcast groups to subscribe to.

flags is a set of additional flags to pass as the second argument to the socket system call—e.g., SOCK_NONBLOCK.

Scheme Procedure: add-socket-membership sock group ¶

Make sock a member of group, an RTNLGRP_ constant, meaning that it will be subscribed to events of that group.

For example, here is how you could create a netlink socket and subscribe it to the “link” group so that it receives notifications for new and removed links:

(let ((sock (connect-route)))
  (add-socket-membership sock RTNLGRP_LINK)
  …)

This procedure is implemented as a setsockopt call.

Scheme Procedure: send-msg msg sock [#:addr] ¶

Send msg (it must be of type message, See Netlink Headers) to addr using sock. If not passed, addr is the address of the kernel.

Scheme Procedure: receive-msg sock [#:addr] ¶

Receives a message from sock from addr. This procedure is blocking. If not passed, addr defaults to the address of the kernel. This procedure returns the message as a bytevector, that you can deserialize with deserialize (See Data Types)

Scheme Procedure: receive-and-decode-msg sock decoder [#:addr] ¶

Receives one or more messages from sock from addr. this procedure is blocking. If not passed, addr defaults to the address of the kernel. This procedure returns a list of messages that were decoded using decoder.

When the answer has the NLM_F_MULTI flag, this procedure decodes the next message, until it receives a NLMSG_DONE message. It returns the list of every netlink messages it received, including the NLMSG_DONE.