# libnetlink

## NAME



           libnetlink - A library for accessing the netlink service
    


## SYNOPSIS



           #include <asm/types.h>
           #include <libnetlink.h>
           #include <linux/netlink.h>
           #include <linux/rtnetlink.h>
    
           int rtnl_open(struct rtnl_handle *rth, unsigned subscriptions)
    
           int rtnl_wilddump_request(struct rtnl_handle *rth, int family, int type)
    
           int rtnl_send(struct rtnl_handle *rth, char *buf, int len)
    
           int rtnl_dump_request(struct rtnl_handle *rth, int type, void *req, int len)
    
           int rtnl_dump_filter(struct rtnl_handle *rth,
                          int (*filter)(struct sockaddr_nl *, struct nlmsghdr *n, void *),
                          void *arg1,
                          int (*junk)(struct sockaddr_nl *,struct nlmsghdr *n, void *),
                          void *arg2)
    
           int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n, pid_t peer,
                      unsigned groups, struct nlmsghdr *answer,
                      int (*junk)(struct sockaddr_nl *,struct nlmsghdr *n, void *),
                      void *jarg)
    
           int rtnl_listen(struct rtnl_handle *rtnl,
                      int (*handler)(struct sockaddr_nl *, struct rtnl_ctrl_data *,
                               struct nlmsghdr *n, void *),
                      void *jarg)
    
           int rtnl_from_file(FILE *rtnl,
                      int (*handler)(struct sockaddr_nl *,struct nlmsghdr *n, void *),
                      void *jarg)
    
           int addattr32(struct nlmsghdr *n, int maxlen, int type, __u32 data)
    
           int addattr_l(struct nlmsghdr *n, int maxlen, int type, void *data, int alen)
    
           int rta_addattr32(struct rtattr *rta, int maxlen, int type, __u32 data)
    
           int rta_addattr_l(struct rtattr *rta, int maxlen, int type, void *data, int alen)
    


## DESCRIPTION



           libnetlink provides a higher level interface to rtnetlink(7).  The
           read functions return 0 on success and a negative errno on
           failure.  The send functions return the amount of data sent, or -1
           on error.
    
           rtnl_open
                  Open a rtnetlink socket and save the state into the **rth**
                  handle. This handle is passed to all subsequent calls.
                  **subscriptions** is a bitmap of the rtnetlink multicast groups
                  the socket will be a member of.
    
           rtnl_wilddump_request
                  Request a full dump of the **type** database for **family**
                  addresses.  **type** is a rtnetlink message type.
    
           rtnl_dump_request
                  Request a full dump of the **type** data buffer into **buf** with
                  maximum length of **len.  type** is a rtnetlink message type.
    
           rtnl_dump_filter
                  Receive netlink data after a request and filter it.  The
                  **filter** callback checks if the received message is wanted.
                  It gets the source address of the message, the message
                  itself and **arg1** as arguments. 0 as return means that the
                  filter passed, a negative value is returned by
                  _rtnl_dump_filter_ in case of error. NULL for _filter_ means to
                  not use a filter.  **junk** is used to filter messages not
                  destined to the local socket.  Only one message bundle is
                  received. If there is a message pending, this function does
                  not block.
    
           rtnl_listen
                  Receive netlink data after a request and pass it to
                  _handler._  **handler** is a callback that gets the message
                  source address, anscillary data, the message itself, and
                  the **jarg** cookie as arguments. It will get called for all
                  received messages.  Only one message bundle is received. If
                  there is a message pending this function does not block.
    
           rtnl_from_file
                  Works like _rtnl_listen,_ but reads a netlink message bundle
                  from the file **file** and passes the messages to **handler** for
                  parsing. The file should contain raw data as received from
                  a rtnetlink socket.
    
           The following functions are useful to construct custom rtnetlink
           messages. For simple database dumping with filtering it is better
           to use the higher level functions above. See rtnetlink(3) and
           netlink(3) on how to generate a rtnetlink message. The following
           utility functions require a continuous buffer that already
           contains a netlink message header and a rtnetlink request.
    
           rtnl_send
                  Send the rtnetlink message in **buf** of length **len** to handle
                  **rth.**
    
           addattr32
                  Add a __u32 attribute of type **type** and with value **data** to
                  netlink message **n,** which is part of a buffer of length
                  **maxlen.**
    
           addattr_l
                  Add a variable length attribute of type **type** and with value
                  **data** and **alen** length to netlink message **n,** which is part of
                  a buffer of length **maxlen.  data** is copied.
    
           rta_addattr32
                  Initialize the rtnetlink attribute **rta** with a __u32 data
                  value.
    
           rta_addattr32
                  Initialize the rtnetlink attribute **rta** with a variable
                  length data value.
    


## BUGS



           This library is meant for internal use, use libmnl for new
           programs.
    
           The functions sometimes use fprintf and exit when a fatal error
           occurs.  This library should be named librtnetlink.
    


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