doc for config module moved from wiki
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frtabu
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# loader source files
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The oai shared library loader is implemented in two source files, located in [common/utils](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils)
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1. [load_module_shlib.c](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils/load_module_shlib.c) contains the loader implementation
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1. [load_module_shlib.h](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils/load_module_shlib.h) is the loader include file containing both private and public data type definitions. It also contain API prototypes.
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[loader home page](loader)
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The configuration module objectives are
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1. Allow easy parameters management in oai, helping the development of a flexible, modularized and fully configurable softmodem.
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1. Use a common configuration API in all oai modules
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1. Allow development of alternative configuration sources without modifying the oai code. Today the only delivered configuration source is the libconfig format configuration file.
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As a developer you may need to look at these sections:
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* [loading a shared library](loader/devusage/loading)
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* [loader API](loader/devusage/api)
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* [loader public structures](loader/devusage/struct)
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Loader usage examples can be found in oai sources:
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* device and transport initialization code: [function `load_lib` in *targets/ARCH/COMMON/__common_lib.c__* ](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/targets/ARCH/COMMON/common_lib.c#L91)
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* turbo encoder and decoder initialization: [function `load_codinglib`in *openair1/PHY/CODING/__coding_load.c__*](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/openair1/PHY/CODING/coding_load.c#L113)
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[loader home page](loader)
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Loader API is defined in the [common/utils/load_module_shlib.h](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/common/utils/load_module_shlib.h) include file.
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```c
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int load_module_shlib(char *modname,loader_shlibfunc_t *farray, int numf)
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```
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* possibly initializes the loader, if it has not been already initialized
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* Formats the full shared library path, using the `modname` argument and the loader `shlibpath` and `shlibversion`configuration parameters.
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* loads the shared library, using the dlopen system call
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* looks for `< modname >_autoinit` symbol, using the `dlsym` system call and possibly call the corresponding function.
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* looks for `< modname >_checkbuildver` symbol, using the `dlsym` system call and possibly calls the corresponding function. If the return value of this call is `-1`, program execution is stopped. It is the responsibility of the shared library developer to implement or not a `< modname >_checkbuildver` function and to decide if a version mismatch is a fatal condition. The `< modname >_checkbuildver` function must match the `checkverfunc_t` function type. The first argument is the main executable version, as set in the `PACKAGE_VERSION` macro defined in the [oai CMakeLists](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/cmake_targets/CMakeLists.txt#L218), around line 218. The second argument points to the shared library version which should be set by the `< modname >_checkbuildver` function.
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* If the farray pointer is null, looks for `< modname >_getfarray` symbol, calls the corresponding function when the symbol is found. `< modname >_getfarray` takes one argument, a pointer to a `loader_shlibfunc_t` array, and returns the number of items in this array, as defined by the `getfarrayfunc_t` type. The `loader_shlibfunc_t` array returned by the shared library must be fully filled (both `fname` and `fptr` fields).
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* looks for the `numf` function symbols listed in the `farray[i].fname` arguments and set the corresponding `farray[i].fptr`function pointers
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```c
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void * get_shlibmodule_fptr(char *modname, char *fname)
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```
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Returns a pointer to the symbol `fname`, defined in module `modname`, or `NULL` if the symbol is not found.
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[loader home page](loader)
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[loader developer home page](loader/devusage)
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Implementing a shared library dynamic load using the oai loader is a two steps task:
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1. define the `loader_shlibfunc_t` array, describing the list of externally available functions implemented in the library. This is the interface of the module.
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1. Call the `load_module_shlib` function, passing it the previously defined array and the number of items in this array. The first argument to `load_module_shlib` is the name identifying the module, which is also used to format the corresponding library name, as described [here](loader/rtusage#shared-library-names)
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After a successful `load__module_shlib` call, the function pointer of each `loader_shlibfunc_t` array item has been set and can be used to call the corresponding function.
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Typical loader usage looks like:
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```c
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/* shared library loader include file */
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#include "common/utils/load_module_shlib.h"
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.............
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/*
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define and initialize the array, describing the list of functions
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implemented in "mymodule"
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*/
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loader_shlibfunc_t mymodule_fdesc[2];
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mymodule_fdesc[0].fname="mymodule_f1";
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mymodule_fdesc[1].fname="mymodule_f2";
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/*
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load the library, it's name must be libmymod.so. Configuration can be
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used to specify a specific path to look for libmymod.so. Configuration
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can also specify a version, for example "V1", in this case the loader
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will look for libmymodV1.so
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*/
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ret=load_module_shlib("mymod",mymodule_fdesc, sizeof(mymodule_fdesc)/sizeof(loader_shlibfunc_t));
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if (ret < 0) {
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fprintf(stderr,"Library couldn't be loaded\n");
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} else {
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/*
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library has been loaded, we probably want to call some functions...
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*/
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ret=((funcf1_t)mymodule_fdesc[0].fptr)();
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..................
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/*
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later and/or somewhere else in the code you may want to call function "mymodule_f2"
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You can use the loader get_shlibmodule_fptr(char *modname, char *fname) function
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to retrieve the pointer to that function
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*/
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funcf2_t *f2;
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int ret;
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int intarg1;
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char *strarg;
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........................
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f2 = (funcf2_t)get_shlibmodule_fptr("mymodule", "mymodule_f2")
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if (f2 != NULL) {
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ret = f2(intarg1,strarg);
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}
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...............
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```
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When loading a shared library the loader looks for a symbol named `< module name > _autoinit` and, if it finds it, calls it. The `autoinit` function is called without any argument and the returned value, if any, is not tested.
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[loader home page](loader)
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[loader developer home page](loader/devusage)
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# `loader_shlibfunc_t`structure
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It is defined in include file [ common/util/load_module_shlib.h ](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/common/utils/load_module_shlib.h#L38). This structure is used to list the symbols that should be searched by the loader when calling the `load_module_shlib` function.
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| Fields | Description | I/O |
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|:-----------|:------------------------------------------------------------------|----:|
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| `fname` | symbol name, is passed to the [`dlsym`](http://man7.org/linux/man-pages/man3/dlsym.3.html) system call performed by the loader to get a pointer to the symbol | I |
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| `fptr` | pointer to the symbol name, set by the loader. `fptr` is defined as a `int (*fptr)(void)` function type | O |
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[loader home page](loader)
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[loader developer home page](loader/devusage)
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## shared library names
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Shared library full names are built by the loader using the format:
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> < *path* >/lib< *module name* >< *module version* >.so
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1. the < *module name* > is defined at development time, it comes from the `modname` argument of the `load_module_shlib` call.
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1. the < *module version* > and < *path* > optional parameters, are defined at run-time, depending on the configuration.
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## loader parameters
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The loader is using the [configuration module](config), and defines global and per library parameters. Global parameters must be specified under the **loader** section and library specific parameters under a **loader.<*module name*>** section. Module specific parameters override the global parameters.
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### Global loader parameters
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| name | type | default | description |
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|:---:|:---:|:---:|:----|
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| `shlibpath` | `string of char` | `""` | directory path used to look for shared libraries, may be superseded by the library specific `shlibpath`.|
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| `maxshlibs` | `integer` | 10 | Maximum number of shared libraries the loader can manage. |
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### library specific loader parameters
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| name | type | default | description |
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|:---:|:---:|:---:|:----|
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| `shlibpath` | `string of char` | `""` | directory path used to look for this shared library.|
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| `shlibversion` | `string of char` | `""` | version to be used to load this shared library.|
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### loader configuration examples
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The following configuration file example just reproduce the default loader parameters:
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```c
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loader :
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{
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shlibpath = "./";
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maxshlibs = 10;
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liboai_device :
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{
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shlibpath = "./";
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shlibversion = "";
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}
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};
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```
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If you want to load a device called *liboai_device_USRP.so* without writting a specific configuration, you can start the softmodem using the following command:
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> ./lte-softmodem -O libconfig:/usr/local/oai/openairinterface5g/targets/PROJECTS/GENERIC-LTE-EPC/CONF/enb.nbiot.band7.tm1.50PRB.usrpb210.conf:dbgl5 --loader.oai_device.shlibversion _USRP
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With this latest example, nn the softmodem logs, you can check that the right device library has been loaded:
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```bash
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[LIBCONFIG] loader.oai_device.shlibpath not found in /usr/local/oai/develop-nb-iot-merge/openairinterface5g/targets/PROJECTS/GENERIC-LTE-EPC/CONF/enb.nbiot.band7.tm1.50PRB.usrpb210.conf
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[LIBCONFIG] loader.oai_device.shlibversion set to default value ""
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[LIBCONFIG] loader.oai_device: 1/2 parameters successfully set, (1 to default value)
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[CONFIG] shlibversion set to _USRP from command line
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[CONFIG] loader.oai_device 1 options set from command line
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```
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[loader home page](loader)
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