1 Netlink Protocol Library 2 3 This library is a clean room re-implementation of libnl 2.0 and 4 re-licensed under Apache 2.0. It was developed primarily to support 5 wpa_supplicant. However, with additional development can be extended 6 to support other netlink applications. 7 8 Netlink Protocol Format (RFC3549) 9 10 +-----------------+-+-------------------+-+ 11 |Netlink Message |P| Generic Netlink |P| 12 | Header |A| Message Header |A| 13 |(struct nlmsghdr)|D|(struct genlmsghdr)|D| 14 +-----------------+-+-------------------+-+-------------+ 15 |len:4|type:2|flags:2|seq:4 pid:4|cmd:1|ver:1|reserved:2| 16 +--------------------------------+----------------------+ 17 +-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+ 18 |Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|...| 19 | #0 Header |A| #0 Payload |A| #1 Header |A| #1 Payload |A| | 20 | (struct nlattr) |D| (void) |D| (struct nlattr) |D| (void) |D| | 21 +-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+ 22 |len:2(==4+payload)|type:2|payload|pad| 23 +-------------------------+-------+---+ 24 25 NETLINK OVERVIEW 26 27 * Each netlink message consists of a bitstream with a netlink header. 28 * After this header a second header *can* be used specific to the netlink 29 family in use. This library was tested using the generic netlink 30 protocol defined by struct genlmsghdr to support nl80211. 31 * After the header(s) netlink attributes can be appended to the message 32 which hold can hold basic types such as unsigned integers and strings. 33 * Attributes can also be nested. This is accomplished by calling "nla_nest_start" 34 which creates an empty attribute with nest attributes as its payload. Then to 35 close the nest, "nla_nest_end" is called. 36 * All data structures in this implementation are byte-aligned (Currently 4 bytes). 37 * Acknowledgements (ACKs) are sent as NLMSG_ERROR netlink message types (0x2) and 38 have an error value of 0. 39 40 KNOWN ISSUES 41 42 GENERAL 43 * Not tested for thread safety 44 45 Android.mk 46 * No dynamic library because of netlink cache not implemented and 47 not tested for thread safety 48 49 attr.c 50 * nla_parse - does not use nla_policy argument 51 52 cache.c 53 * netlink cache not implemented and only supports one netlink family id 54 which is stored in the nl_cache pointer instead of an actual cache 55 56 netlink.c 57 * nl_recvmsgs - does not support nl_cb_overwrite_recv() 58 * nl_recv - sets/unsets asynchronous socket flag 59 60 SOURCE FILES 61 62 * Android.mk - Android makefile 63 * README - This file 64 * attr.c - Netlink attributes 65 * cache.c - Netlink cache 66 * genl/family.c - Generic netlink family id 67 * genl/genl.c - Generic netlink 68 * handlers.c - Netlink callbacks 69 * msg.c - Netlink messages construction 70 * netlink.c - Netlink socket communication 71 * object.c - libnl object wrapper 72 * socket.c - Netlink kernel socket utils 73 74 IMPORTANT HEADER FILES - NOTE: These are based on the the origin GPL libnl headers 75 76 * netlink-types.h - Contains many important structs for libnl 77 to represent netlink objects 78 * netlink/netlink-kernel.h - Netlink kernel headers and field constants. 79 * netlink/msg.h - macros for iterating over netlink messages 80 * netlink/attr.h - netlink attribute constants, iteration macros and setters 81 82 REFERENCES 83 84 * nl80211.h 85 * netlink_types.h 86 * $LINUX_KERNEL/net/wireless/nl80211.c 87 * http://www.infradead.org/~tgr/libnl/doc-3.0/index.html 88 * http://www.netfilter.org/projects/libmnl/doxygen/index.html 89
