doc UPDATE datastore plugins MONGO DS and REDIS DS

README.md

@@ -82,12 +82,12 @@ other users.
 #### Optional
 
 * pkg-config & libsystemd (to support `sysrepo-plugind` systemd service)
+* [mongodb-org](https://www.mongodb.com/docs/manual/installation/); [libmongoc](https://mongoc.org/libmongoc) >= 1.24.0; libbson >= 1.24.0 (for MONGO DS datastore plugin)
+* [redis-stack-server](https://redis.io/docs/latest/operate/oss_and_stack/install/install-stack/); [hiredis](https://github.com/redis/hiredis) >= 1.1.0 (for REDIS DS datastore plugin)
 * doxygen (for generating documentation)
 * cmocka >= 1.0.1 (for tests only, see [Tests](#Tests))
 * valgrind (for enhanced testing)
-* gcov (for code coverage)
-* lcov (for code coverage)
-* genhtml (for code coverage)
+* gcov; lcov; genhtml (for code coverage)
 
 ## Building
 
@@ -275,6 +275,42 @@ an internal subscription to the `/ietf-factory-default:factory-reset` RPC which
 able to subscribe to it with higher or lower priority and perform any other tasks required for a device
 to be rest to its factory settings.
 
+## Datastore plugins
+
+In sysrepo there are three internal datastore plugins (`JSON DS file`, `MONGO DS` and `REDIS DS`). The default datastore
+plugin is `JSON DS file` which stores all the data to JSON files. `MONGO DS` and `REDIS DS` store data to a database and can be used
+as the default datastore plugins for various datastores after setting a few CMake
+variables. For every datastore a different default datastore plugin can be set. For example:
+
+`cmake -DDEFAULT_STARTUP_DS_PLG="MONGO DS" -DDEFAULT_RUNNING_DS_PLG="MONGO DS" -DDEFAULT_CANDIDATE_DS_PLG="REDIS DS" -DDEFAULT_OPERATIONAL_DS_PLG="JSON DS file" -DDEFAULT_FACTORY_DEFAULT_DS_PLG="JSON DS file" ..`
+
+The shared memory prefix set by `SYSREPO_SHM_PREFIX` is used by each plugin to isolate data between separate *sysrepo* "instances".
+`JSON DS file` includes it in the name of every file it creates, whereas `MONGO DS` includes it
+in the name of every collection and lastly `REDIS DS` includes it in the name of every key as a part of the prefix.
+For more information about plugins, see [plugin documentation](doc/sr_plugins.dox).
+
+### MONGO DS
+
+To use `MONGO DS` datastore plugin, **libmongoc** and **libbson** libraries have to be present
+on the system. Additionally a running MongoDB server has to be available to the system. By default
+sysrepo assumes that the server is available at the loopback address `127.0.0.1` and port `27017` with
+no authentication needed. For different IP address and port, set `MONGO_HOST` and `MONGO_PORT` CMake
+variables. For the authentication via username and password, set `MONGO_USERNAME` and `MONGO_PASSWORD`
+CMake variables. Please note that for sysrepo to correctly authenticate, an existing user with sufficient rights
+and with the configured username and password has to be available
+on the server. Also if the user is created on a different database than `admin`, provide the correct database name on which the user was created
+via the `MONGO_AUTHSOURCE` CMake variable. Lastly, for the authentication to work, authentication has to be enabled in the server configuration (see [Official MongoDB documentation](https://www.mongodb.com/docs/manual/administration/security-checklist/#std-label-checklist-auth)).
+For more information on how the plugin works, please refer to the [plugin documentation](doc/sr_plugins.dox).
+
+### REDIS DS
+
+Similarly to `MONGO DS`, to use `REDIS DS` datastore plugin, **libhiredis** client library and Redis Stack server have to be available to the system.
+The default server address `127.0.0.1` and port `6379` are assumed with
+no authentication needed. For different IP address and port, set `REDIS_HOST` and `REDIS_PORT` CMake variables. 
+To enable authentication via a username and password, set `REDIS_USERNAME` and `REDIS_PASSWORD` CMake variables,
+create a corresponding user with sufficient rights, and do not forget to enforce the authentication on the server (see [official Redis documentation](https://redis.io/docs/latest/commands/auth/)).
+For more information on how the plugin works, please refer to the [plugin documentation](doc/sr_plugins.dox).
+
 ## Examples
 
 See [examples](examples) directory, which contains an example for basic API functions.

doc/sr_plugins.dox

@@ -28,4 +28,35 @@ implementation.
 
 @ref ntfplg_api
 
+@section sr_ds_plg_mongo MONGO DS plugin
+
+`MONGO DS` plugin works as a database client. It connects and sends necessary commands directly to the MongoDB database
+server. It connects via the **libmongoc** library API and uses its functions to further communicate with the server.
+In MongoDB database there is a hierarchy of data. All data are stored in records which are then stored in collections
+which are then stored in databases. Each datastore for which `MONGO DS` plugin was deployed has its own database.
+The name of the database consists of a `sr_` prefix and the name of the datastore, e.g. `sr_factory-default`. Data of each
+particular YANG module are then stored in a collection within the particular database. In order to avoid data
+conflicts the databases with the names `sr_startup`, `sr_running`, `sr_candidate`, `sr_operational` and `sr_factory-default`
+can only be used by the sysrepo library.
+
+In order for the authentication (see README) to work the configured user has to have a read and a write permission on
+following databases: `sr_startup`, `sr_running`, `sr_candidate`, `sr_operational` and `sr_factory-default`.
+
+@section sr_ds_plg_redis REDIS DS plugin
+
+`REDIS DS` plugin first connects to the Redis Stack database server via **hiredis** library API and then sends 
+commands to the server using its functions. In Redis database all data are stored together. In order to differentiate between them,
+the keys have to be prefixed. The prefix for all sysrepo data is `sr:` and in order to avoid data conflicts the keys and indexes
+starting with a `sr:` prefix can only be used by the sysrepo library.
+
+In Redis database there are certain limits with respect to data management which cannot be set to unlimited. The maximum amount
+of data which can be loaded from the database at once is set to one trillion. Some of these limits are enforced via the server
+configuration and since the sysrepo library does not have an access to the server's configuration file, it sets these limits
+via commands (more specifically the options MAXAGGREGATERESULTS and MAXEXPANSIONS).
+
+In order for the authentication (see README) to work the user has to have the right to operate on all keys and indexes with the prefix `sr:` and 
+at least the right to use these following commands: `AUTH`, `FT.CONFIG SET`, `FT.AGGREGATE`, `FT.CURSOR READ`, `FT.CREATE`,
+`FT.DROPINDEX`, `HSET`, `HGET`, `SET`, `GET`, `DEL`, `COPY`. Redis supports categories of commands, so to enable all of these commands
+at once you only have to enable a category containing all of them, e.g. `@all`.
+
 */