a63a9ec808
This reverts commit 7097f052d9.
libnl_2 needs to stay in AOSP for now for compatibility with
GPL test builds.
88 lines
3.4 KiB
Text
88 lines
3.4 KiB
Text
Netlink Protocol Library
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This library is a clean room re-implementation of libnl 2.0 and
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re-licensed under Apache 2.0. It was developed primarily to support
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wpa_supplicant. However, with additional development can be extended
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to support other netlink applications.
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Netlink Protocol Format (RFC3549)
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+-----------------+-+-------------------+-+
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|Netlink Message |P| Generic Netlink |P|
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| Header |A| Message Header |A|
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|(struct nlmsghdr)|D|(struct genlmsghdr)|D|
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+-----------------+-+-------------------+-+-------------+
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|len:4|type:2|flags:2|seq:4 pid:4|cmd:1|ver:1|reserved:2|
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+--------------------------------+----------------------+
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+-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+
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|Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|Netlink Attribute|P|...|
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| #0 Header |A| #0 Payload |A| #1 Header |A| #1 Payload |A| |
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| (struct nlattr) |D| (void) |D| (struct nlattr) |D| (void) |D| |
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+-----------------+-+-----------------+-+-----------------+-+-----------------+-+---+
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|len:2(==4+payload)|type:2|payload|pad|
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+-------------------------+-------+---+
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NETLINK OVERVIEW
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* Each netlink message consists of a bitstream with a netlink header.
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* After this header a second header *can* be used specific to the netlink
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family in use. This library was tested using the generic netlink
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protocol defined by struct genlmsghdr to support nl80211.
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* After the header(s) netlink attributes can be appended to the message
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which hold can hold basic types such as unsigned integers and strings.
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* Attributes can also be nested. This is accomplished by calling "nla_nest_start"
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which creates an empty attribute with nest attributes as its payload. Then to
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close the nest, "nla_nest_end" is called.
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* All data structures in this implementation are byte-aligned (Currently 4 bytes).
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* Acknowledgements (ACKs) are sent as NLMSG_ERROR netlink message types (0x2) and
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have an error value of 0.
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KNOWN ISSUES
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GENERAL
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* Not tested for thread safety
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Android.mk
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* No dynamic library because of netlink cache not implemented and
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not tested for thread safety
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attr.c
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* nla_parse - does not use nla_policy argument
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cache.c
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* netlink cache not implemented and only supports one netlink family id
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which is stored in the nl_cache pointer instead of an actual cache
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netlink.c
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* nl_recvmsgs - does not support nl_cb_overwrite_recv()
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* nl_recv - sets/unsets asynchronous socket flag
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SOURCE FILES
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* Android.mk - Android makefile
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* README - This file
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* attr.c - Netlink attributes
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* cache.c - Netlink cache
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* genl/family.c - Generic netlink family id
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* genl/genl.c - Generic netlink
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* handlers.c - Netlink callbacks
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* msg.c - Netlink messages construction
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* netlink.c - Netlink socket communication
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* object.c - libnl object wrapper
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* socket.c - Netlink kernel socket utils
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IMPORTANT HEADER FILES - NOTE: These are based on the the origin GPL libnl headers
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* netlink-types.h - Contains many important structs for libnl
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to represent netlink objects
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* netlink/netlink-kernel.h - Netlink kernel headers and field constants.
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* netlink/msg.h - macros for iterating over netlink messages
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* netlink/attr.h - netlink attribute constants, iteration macros and setters
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REFERENCES
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* nl80211.h
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* netlink_types.h
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* $LINUX_KERNEL/net/wireless/nl80211.c
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* http://www.infradead.org/~tgr/libnl/doc-3.0/index.html
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* http://www.netfilter.org/projects/libmnl/doxygen/index.html
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