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* lib/genl/genl.c Generic Netlink
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation version 2.1
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* Copyright (c) 2003-2008 Thomas Graf <tgraf@suug.ch>
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* @defgroup genl Generic Netlink
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* <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
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* +----------------------------+- - -+- - - - - - - - - - -+- - -+
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* | Header | Pad | Payload | Pad |
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* | struct nlmsghdr | | | |
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* +----------------------------+- - -+- - - - - - - - - - -+- - -+
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* <-------- GENL_HDRLEN -------> <--- hdrlen -->
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* <------- genlmsg_len(ghdr) ------>
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* +------------------------+- - -+---------------+- - -+------------+
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* | Generic Netlink Header | Pad | Family Header | Pad | Attributes |
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* | struct genlmsghdr | | | | |
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* +------------------------+- - -+---------------+- - -+------------+
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* genlmsg_data(ghdr)--------------^ ^
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* genlmsg_attrdata(ghdr, hdrlen)-------------------------
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* #include <netlink/netlink.h>
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* #include <netlink/genl/genl.h>
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* #include <netlink/genl/ctrl.h>
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* struct nl_sock *sock;
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* // Allocate a new netlink socket
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* sock = nl_socket_alloc();
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* // Connect to generic netlink socket on kernel side
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* // Ask kernel to resolve family name to family id
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* family = genl_ctrl_resolve(sock, "generic_netlink_family_name");
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* // Construct a generic netlink by allocating a new message, fill in
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* // the header and append a simple integer attribute.
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* msg = nlmsg_alloc();
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* genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, family, 0, NLM_F_ECHO,
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* CMD_FOO_GET, FOO_VERSION);
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* nla_put_u32(msg, ATTR_FOO, 123);
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* // Send message over netlink socket
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* nl_send_auto_complete(sock, msg);
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* // Prepare socket to receive the answer by specifying the callback
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* // function to be called for valid messages.
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* nl_socket_modify_cb(sock, NL_CB_VALID, NL_CB_CUSTOM, parse_cb, NULL);
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* // Wait for the answer and receive it
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* nl_recvmsgs_default(sock);
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* static int parse_cb(struct nl_msg *msg, void *arg)
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* struct nlmsghdr *nlh = nlmsg_hdr(msg);
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* struct nlattr *attrs[ATTR_MAX+1];
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* // Validate message and parse attributes
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* genlmsg_parse(nlh, 0, attrs, ATTR_MAX, policy);
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* if (attrs[ATTR_FOO]) {
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* uint32_t value = nla_get_u32(attrs[ATTR_FOO]);
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#include <netlink-generic.h>
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#include <netlink/netlink.h>
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#include <netlink/genl/genl.h>
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#include <netlink/utils.h>
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* @name Socket Creating
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int genl_connect(struct nl_sock *sk)
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return nl_connect(sk, NETLINK_GENERIC);
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* Send trivial generic netlink message
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* @arg sk Netlink socket.
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* @arg family Generic netlink family
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* @arg version Version
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* @arg flags Additional netlink message flags.
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* Fills out a routing netlink request message and sends it out
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* using nl_send_simple().
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* @return 0 on success or a negative error code.
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int genl_send_simple(struct nl_sock *sk, int family, int cmd,
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int version, int flags)
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struct genlmsghdr hdr = {
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return nl_send_simple(sk, family, flags, &hdr, sizeof(hdr));
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* @name Message Parsing
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int genlmsg_valid_hdr(struct nlmsghdr *nlh, int hdrlen)
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struct genlmsghdr *ghdr;
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if (!nlmsg_valid_hdr(nlh, GENL_HDRLEN))
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ghdr = nlmsg_data(nlh);
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if (genlmsg_len(ghdr) < NLMSG_ALIGN(hdrlen))
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int genlmsg_validate(struct nlmsghdr *nlh, int hdrlen, int maxtype,
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struct nla_policy *policy)
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struct genlmsghdr *ghdr;
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if (!genlmsg_valid_hdr(nlh, hdrlen))
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return -NLE_MSG_TOOSHORT;
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ghdr = nlmsg_data(nlh);
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return nla_validate(genlmsg_attrdata(ghdr, hdrlen),
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genlmsg_attrlen(ghdr, hdrlen), maxtype, policy);
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int genlmsg_parse(struct nlmsghdr *nlh, int hdrlen, struct nlattr *tb[],
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int maxtype, struct nla_policy *policy)
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struct genlmsghdr *ghdr;
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if (!genlmsg_valid_hdr(nlh, hdrlen))
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return -NLE_MSG_TOOSHORT;
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ghdr = nlmsg_data(nlh);
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return nla_parse(tb, maxtype, genlmsg_attrdata(ghdr, hdrlen),
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genlmsg_attrlen(ghdr, hdrlen), policy);
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* Get head of message payload
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* @arg gnlh genetlink messsage header
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void *genlmsg_data(const struct genlmsghdr *gnlh)
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return ((unsigned char *) gnlh + GENL_HDRLEN);
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* Get lenght of message payload
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* @arg gnlh genetlink message header
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int genlmsg_len(const struct genlmsghdr *gnlh)
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struct nlmsghdr *nlh = (struct nlmsghdr *)((unsigned char *)gnlh -
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return (nlh->nlmsg_len - GENL_HDRLEN - NLMSG_HDRLEN);
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* Get head of attribute data
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* @arg gnlh generic netlink message header
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* @arg hdrlen length of family specific header
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struct nlattr *genlmsg_attrdata(const struct genlmsghdr *gnlh, int hdrlen)
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return genlmsg_data(gnlh) + NLMSG_ALIGN(hdrlen);
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* Get length of attribute data
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* @arg gnlh generic netlink message header
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* @arg hdrlen length of family specific header
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int genlmsg_attrlen(const struct genlmsghdr *gnlh, int hdrlen)
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return genlmsg_len(gnlh) - NLMSG_ALIGN(hdrlen);
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* @name Message Building
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* Add generic netlink header to netlink message
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* @arg msg netlink message
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* @arg pid netlink process id or NL_AUTO_PID
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* @arg seq sequence number of message or NL_AUTO_SEQ
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* @arg family generic netlink family
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* @arg hdrlen length of user specific header
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* @arg flags message flags
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* @arg cmd generic netlink command
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* @arg version protocol version
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* Returns pointer to user specific header.
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void *genlmsg_put(struct nl_msg *msg, uint32_t pid, uint32_t seq, int family,
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int hdrlen, int flags, uint8_t cmd, uint8_t version)
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struct nlmsghdr *nlh;
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struct genlmsghdr hdr = {
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nlh = nlmsg_put(msg, pid, seq, family, GENL_HDRLEN + hdrlen, flags);
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memcpy(nlmsg_data(nlh), &hdr, sizeof(hdr));
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NL_DBG(2, "msg %p: Added generic netlink header cmd=%d version=%d\n",
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return nlmsg_data(nlh) + GENL_HDRLEN;
added
removed
lib/genl/genl.c
