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Anonymous, 02/19/2016 10:49 PM

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[[PageOutline]]
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= libosmocore =
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libosmocore is a library with various utility functions that were originally developed as part of 
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the [wiki:OpenBSC] project, but which are of a more generic nature and thus useful to (at least)
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other programs that we develop in the sphere of Free Software / Open Source mobile communications.
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There is no clear scope of it.  We simply move all shared code between [wiki:OsmocomBB] and [wiki:OpenBSC]
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in this library to avoid code duplication.
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To build osmocom-bb it is mandatory to install libosmocom in advance.
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== Browsing its source code ==
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You can do that using our cgit installation at http://cgit.osmocom.org/cgit/libosmocore/
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== Obtaining it ==
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To obtain libosmocore, you can use the following git URL:
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{{{git clone git://git.osmocom.org/libosmocore.git}}}
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== Compiling and installing it ==
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To compile and install it as standalone:
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{{{
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cd libosmocore/
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autoreconf -i
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./configure
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make
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sudo make install
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cd ..
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}}}
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== Licensing ==
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This library is GPL licensed, as the code is taken from the similarly GPL-licensed OpenBSC codebase.
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This means you '''cannot use this library from non-GPL licensed code without infringing copyright!
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== Features ==
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=== Select loop abstraction ===
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This is implemented in select.[ch] and enables you to build complex asynchronous/non-blocking I/O
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programs in a single thread.
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=== Message buffer handling ===
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Inspired by the Linux kernel {{{struct sk_buff}}}, this is our message buffer {{{struct msgb}}}
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implementation.  It provides handling of packet buffers, putting them in queues, prepending
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and appending data to it, etc.
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=== Bitvector ===
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A convenient set of routines to deal with bit-vectors in C.  This was originally written
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for rest-octet parsing.
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=== TLV handling ===
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The GSM Layer3 and above are full of TV / TLV / TL16V and other data fields.  Our implementation
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provides parser and generator functions, tightly coupled to {{{struct msgb}}}
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=== Timers ===
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Provides a timer core where you can register timers with a callback function. The function
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is called when the timer expires.
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=== Comp128v1 ===
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A Comp128v1 implementation by Sylvain Munaut is included.
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=== Rate Counter ===
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Provides infrastructure for maintaining ''rate counters'', i.e. counters that can be incremented
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and will also keep track of the rate of events per second, minute, hour and day.  A group of rate
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counters is defined as an abstract ''class'', from which you can then allocate instances.  The
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''class'' description includes information about the counter names.
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=== Protocol helper code ===
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==== GSM utils ====
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 * conversion functions for ARFCN, RxLevel, 7bit GSM character set, power level, frame numbers, ...
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==== GSM 04.08 ====
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 * extensive header files for the GSM 04.08 (Layer 3 RR/MM/CC) messages
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 * TLV parser definitions to parse the optional IEs
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 * utility functions such as
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  * human readable strings for RR cause names
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  * converting GSM Mobile Identities (MI) to string and back
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 * encoding and decoding functions for call control IEs
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==== GSM 08.08 (A Interface) ====
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 * API to wrap 04.08 messages in BSSMAP/DTAP message
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 * TLV parser definitions
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==== GSM 08.58 (A-bis RSL) ====
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 * header file with structure and enum definitions for GSM 08.58 protocol
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 * TLV parser definitions for RSL optional IEs
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 * human readable strings for RSL Error values and RLM cause values
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 * encoding and decoding of RSL channel number
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==== GSM 12.21 (A-bis OML) ====
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 * header file with structure and enum definitions for GSM 12.21 (and 08.59) protocol
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==== GSM 04.11 (SMS) ====
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 * header file with structure and enum definitions for GSM 04.11 (SMS RP and CP layers) protocol
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=== Talloc memory allocator ===
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The talloc memory allocator from the Samba project is (optionally) part of libosmocore.
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It provides hierarchical memory allocation and extensive debugging features such as dumping
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the currently allocated objects (at runtime) to the console.
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=== Logging framework ===
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A generic logging implementation, supporting a dynamic number of 'log targets', understanding
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the notion of log levels and log categories.  Filtering based on levels and categories is
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implemented in the core, while context-specific filtering can be implemented by the application
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using libosmocore.
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 * logging with various log levels for various subsystems inside the application
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 * logging to stderr, syslog or application-defined targets
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 * runtime reconfigurable per-subsystem log levels
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 * timestamping of log lines
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 * colorized log output
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=== Write Queue ===
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This is a write queue implementation on top of libosmocore's select loop abstraction.
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It allows you to simply say "write this msg_buff to this file descriptor as soon as
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the file descriptor is writable".
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== Development Cycle ==
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As we are still developing the GSM protocol stacks on the network side (OpenBSC) and phone side (OsmocomBB),
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every so often there is a need to add some new code to libosmocore.  Even worse, we sometimes need to break
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the API and ABI of the library.
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However, by keeping libosmocore in a separate git repository, we run into one problem: Checking out an old
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version of e.g. OpenBSC or OsmocomBB will result in failed builds, as we don't remember which old version
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of libosmocore was required.  This makes debugging and things like git bisect very hard to impossible.
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In order to solve this problem, we use [http://github.com/apenwarr/git-subtree git-subtree] to import the
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full libosmocore.git repository into OsmocomBB.
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This way, we ensure that there is always a compatible version of libosmocore inside the tree if we check out
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old OsmocomBB versions from git.
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=== Making changes to libosmocore ===
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 '''NEVER COMMIT CHANGES DIRECTLY TO osmocom-bb.git:src/shared/libosmocore'''
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Instead, use the following process:
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 1. make your changes to your local copy of libosmocore
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 1. test them together with OsmocomBB and OpenBSC
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 1. test if libosmocore still builds for both host and target (ARM)
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 1. create a ''diff'' of your local libosmocore changes
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 1. apply that diff to the libosmocore.git repository
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 1. use the script in osmocom-bb.git/src/shared/update-libosmocore.sh (uses git-subtree) to import your changes from libosmocore.git
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 1. test + commit your OsmocomBB changes that depend on the newly introduced code to libosmocore
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It is important that the steps are followed in the order state above to ensure consistency of our repositories
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