Netlink Messages and Attributes Interface

/* ========================================================================
 *         Netlink Messages and Attributes Interface (As Seen On TV)
 * ------------------------------------------------------------------------
 *                          Messages Interface
 * ------------------------------------------------------------------------
 *
 * Message Format:
 *    <--- nlmsg_total_size(payload)  --->
 *    <-- nlmsg_msg_size(payload) ->
 *   +----------+- - -+-------------+- - -+-------- - -
 *   | nlmsghdr | Pad |   Payload   | Pad | nlmsghdr
 *   +----------+- - -+-------------+- - -+-------- - -
 *   nlmsg_data(nlh)---^                   ^
 *   nlmsg_next(nlh)-----------------------+
 *
 * Payload Format:
 *    <---------------------- nlmsg_len(nlh) --------------------->
 *    <------ hdrlen ------>       <- nlmsg_attrlen(nlh, hdrlen) ->
 *   +----------------------+- - -+--------------------------------+
 *   |     Family Header    | Pad |           Attributes           |
 *   +----------------------+- - -+--------------------------------+
 *   nlmsg_attrdata(nlh, hdrlen)---^
 *
 * Data Structures:
 *   struct nlmsghdr			netlink message header
 *
 * Message Construction:
 *   nlmsg_new()			create a new netlink message
 *   nlmsg_put()			add a netlink message to an skb
 *   nlmsg_put_answer()			callback based nlmsg_put()
 *   nlmsg_end()			finalize netlink message
 *   nlmsg_get_pos()			return current position in message
 *   nlmsg_trim()			trim part of message
 *   nlmsg_cancel()			cancel message construction
 *   nlmsg_free()			free a netlink message
 *
 * Message Sending:
 *   nlmsg_multicast()			multicast message to several groups
 *   nlmsg_unicast()			unicast a message to a single socket
 *   nlmsg_notify()			send notification message
 *
 * Message Length Calculations:
 *   nlmsg_msg_size(payload)		length of message w/o padding
 *   nlmsg_total_size(payload)		length of message w/ padding
 *   nlmsg_padlen(payload)		length of padding at tail
 *
 * Message Payload Access:
 *   nlmsg_data(nlh)			head of message payload
 *   nlmsg_len(nlh)			length of message payload
 *   nlmsg_attrdata(nlh, hdrlen)	head of attributes data
 *   nlmsg_attrlen(nlh, hdrlen)		length of attributes data
 *
 * Message Parsing:
 *   nlmsg_ok(nlh, remaining)		does nlh fit into remaining bytes?
 *   nlmsg_next(nlh, remaining)		get next netlink message
 *   nlmsg_parse()			parse attributes of a message
 *   nlmsg_find_attr()			find an attribute in a message
 *   nlmsg_for_each_msg()		loop over all messages
 *   nlmsg_validate()			validate netlink message incl. attrs
 *   nlmsg_for_each_attr()		loop over all attributes
 *
 * Misc:
 *   nlmsg_report()			report back to application?
 *
 * ------------------------------------------------------------------------
 *                          Attributes Interface
 * ------------------------------------------------------------------------
 *
 * Attribute Format:
 *    <------- nla_total_size(payload) ------->
 *    <---- nla_attr_size(payload) ----->
 *   +----------+- - -+- - - - - - - - - +- - -+-------- - -
 *   |  Header  | Pad |     Payload      | Pad |  Header
 *   +----------+- - -+- - - - - - - - - +- - -+-------- - -
 *                     <- nla_len(nla) ->      ^
 *   nla_data(nla)----^                        |
 *   nla_next(nla)-----------------------------'
 *
 * Data Structures:
 *   struct nlattr			netlink attribute header
 *
 * Attribute Construction:
 *   nla_reserve(skb, type, len)	reserve room for an attribute
 *   nla_reserve_nohdr(skb, len)	reserve room for an attribute w/o hdr
 *   nla_put(skb, type, len, data)	add attribute to skb
 *   nla_put_nohdr(skb, len, data)	add attribute w/o hdr
 *   nla_append(skb, len, data)		append data to skb
 *
 * Attribute Construction for Basic Types:
 *   nla_put_u8(skb, type, value)	add u8 attribute to skb
 *   nla_put_u16(skb, type, value)	add u16 attribute to skb
 *   nla_put_u32(skb, type, value)	add u32 attribute to skb
 *   nla_put_u64_64bit(skb, type,
 *                     value, padattr)	add u64 attribute to skb
 *   nla_put_s8(skb, type, value)	add s8 attribute to skb
 *   nla_put_s16(skb, type, value)	add s16 attribute to skb
 *   nla_put_s32(skb, type, value)	add s32 attribute to skb
 *   nla_put_s64(skb, type, value,
 *               padattr)		add s64 attribute to skb
 *   nla_put_string(skb, type, str)	add string attribute to skb
 *   nla_put_flag(skb, type)		add flag attribute to skb
 *   nla_put_msecs(skb, type, jiffies,
 *                 padattr)		add msecs attribute to skb
 *   nla_put_in_addr(skb, type, addr)	add IPv4 address attribute to skb
 *   nla_put_in6_addr(skb, type, addr)	add IPv6 address attribute to skb
 *
 * Nested Attributes Construction:
 *   nla_nest_start(skb, type)		start a nested attribute
 *   nla_nest_end(skb, nla)		finalize a nested attribute
 *   nla_nest_cancel(skb, nla)		cancel nested attribute construction
 *
 * Attribute Length Calculations:
 *   nla_attr_size(payload)		length of attribute w/o padding
 *   nla_total_size(payload)		length of attribute w/ padding
 *   nla_padlen(payload)		length of padding
 *
 * Attribute Payload Access:
 *   nla_data(nla)			head of attribute payload
 *   nla_len(nla)			length of attribute payload
 *
 * Attribute Payload Access for Basic Types:
 *   nla_get_u8(nla)			get payload for a u8 attribute
 *   nla_get_u16(nla)			get payload for a u16 attribute
 *   nla_get_u32(nla)			get payload for a u32 attribute
 *   nla_get_u64(nla)			get payload for a u64 attribute
 *   nla_get_s8(nla)			get payload for a s8 attribute
 *   nla_get_s16(nla)			get payload for a s16 attribute
 *   nla_get_s32(nla)			get payload for a s32 attribute
 *   nla_get_s64(nla)			get payload for a s64 attribute
 *   nla_get_flag(nla)			return 1 if flag is true
 *   nla_get_msecs(nla)			get payload for a msecs attribute
 *
 * Attribute Misc:
 *   nla_memcpy(dest, nla, count)	copy attribute into memory
 *   nla_memcmp(nla, data, size)	compare attribute with memory area
 *   nla_strlcpy(dst, nla, size)	copy attribute to a sized string
 *   nla_strcmp(nla, str)		compare attribute with string
 *
 * Attribute Parsing:
 *   nla_ok(nla, remaining)		does nla fit into remaining bytes?
 *   nla_next(nla, remaining)		get next netlink attribute
 *   nla_validate()			validate a stream of attributes
 *   nla_validate_nested()		validate a stream of nested attributes
 *   nla_find()				find attribute in stream of attributes
 *   nla_find_nested()			find attribute in nested attributes
 *   nla_parse()			parse and validate stream of attrs
 *   nla_parse_nested()			parse nested attribuets
 *   nla_for_each_attr()		loop over all attributes
 *   nla_for_each_nested()		loop over the nested attributes
 *=========================================================================
 */