DO NOT MERGE: Revert "delete libnl_2"
This reverts commit 7097f052d946bc9fbe298c7a88e1d943f54f684e.
libnl_2 needs to stay in AOSP for now for compatibility with
GPL test builds.
diff --git a/libnl_2/README b/libnl_2/README
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+Netlink Protocol Library
+
+This library is a clean room re-implementation of libnl 2.0 and
+re-licensed under Apache 2.0. It was developed primarily to support
+wpa_supplicant. However, with additional development can be extended
+to support other netlink applications.
+
+Netlink Protocol Format (RFC3549)
+
++-----------------+-+-------------------+-+
+|Netlink Message |P| Generic Netlink |P|
+| Header |A| Message Header |A|
+|(struct nlmsghdr)|D|(struct genlmsghdr)|D|
++-----------------+-+-------------------+-+-------------+
+|len:4|type:2|flags:2|seq:4 pid:4|cmd:1|ver:1|reserved:2|
++--------------------------------+----------------------+
++-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+
+|Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|...|
+| #0 Header |A| #0 Payload |A| #1 Header |A| #1 Payload |A| |
+| (struct nlattr) |D| (void) |D| (struct nlattr) |D| (void) |D| |
++-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+
+|len:2(==4+payload)|type:2|payload|pad|
++-------------------------+-------+---+
+
+NETLINK OVERVIEW
+
+* Each netlink message consists of a bitstream with a netlink header.
+* After this header a second header *can* be used specific to the netlink
+ family in use. This library was tested using the generic netlink
+ protocol defined by struct genlmsghdr to support nl80211.
+* After the header(s) netlink attributes can be appended to the message
+ which hold can hold basic types such as unsigned integers and strings.
+* Attributes can also be nested. This is accomplished by calling "nla_nest_start"
+ which creates an empty attribute with nest attributes as its payload. Then to
+ close the nest, "nla_nest_end" is called.
+* All data structures in this implementation are byte-aligned (Currently 4 bytes).
+* Acknowledgements (ACKs) are sent as NLMSG_ERROR netlink message types (0x2) and
+ have an error value of 0.
+
+KNOWN ISSUES
+
+ GENERAL
+ * Not tested for thread safety
+
+ Android.mk
+ * No dynamic library because of netlink cache not implemented and
+ not tested for thread safety
+
+ attr.c
+ * nla_parse - does not use nla_policy argument
+
+ cache.c
+ * netlink cache not implemented and only supports one netlink family id
+ which is stored in the nl_cache pointer instead of an actual cache
+
+ netlink.c
+ * nl_recvmsgs - does not support nl_cb_overwrite_recv()
+ * nl_recv - sets/unsets asynchronous socket flag
+
+SOURCE FILES
+
+* Android.mk - Android makefile
+* README - This file
+* attr.c - Netlink attributes
+* cache.c - Netlink cache
+* genl/family.c - Generic netlink family id
+* genl/genl.c - Generic netlink
+* handlers.c - Netlink callbacks
+* msg.c - Netlink messages construction
+* netlink.c - Netlink socket communication
+* object.c - libnl object wrapper
+* socket.c - Netlink kernel socket utils
+
+IMPORTANT HEADER FILES - NOTE: These are based on the the origin GPL libnl headers
+
+* netlink-types.h - Contains many important structs for libnl
+ to represent netlink objects
+* netlink/netlink-kernel.h - Netlink kernel headers and field constants.
+* netlink/msg.h - macros for iterating over netlink messages
+* netlink/attr.h - netlink attribute constants, iteration macros and setters
+
+REFERENCES
+
+* nl80211.h
+* netlink_types.h
+* $LINUX_KERNEL/net/wireless/nl80211.c
+* http://www.infradead.org/~tgr/libnl/doc-3.0/index.html
+* http://www.netfilter.org/projects/libmnl/doxygen/index.html