config-linux: add an initial spec of RDMA related field

This commit adds an initial spec of RDMA related field for Linux
configuration. They will be used for controlling rdmacg of the Linux
kernel.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>

config-linux.md

@@ -637,6 +637,30 @@ The following parameters can be specified to set up seccomp:
     "mountLabel": "system_u:object_r:svirt_sandbox_file_t:s0:c715,c811"
 ```
 
+### <a name="configLinuxRdmaLimits" />RDMA resource limits
+
+**`rdma_limits`** (array of objects, OPTIONAL) represents the `rdma` controller which allows to limit the
+resources related to network interfaces which support RDMA (e.g. HCA handles).
+For more information, see the RDMA section of [the kernel cgroups documentation][cgroup-v2].
+
+Each entry has the following structure:
+
+* **`interface_name`** *(string, REQUIRED)* - a name of an interface
+* **`hca_handle_limit`** *(int64, REQUIRED)* - limit a number of HCA handles which can be used by a container (-1 means max)
+* **`hca_object_limit`** *(int64, REQUIRED)* - limit a number of HCA objects which can be used by a container (-1 means max)
+
+#### Example
+
+```json
+    "rdma_limits": [
+        {
+            "interface_name": "mlx5_0",
+            "hca_handle_limit": 1,
+	    "hca_object_limit": 20
+        }
+   ]
+```
+
 
 [cgroup-v1]: https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
 [cgroup-v1-blkio]: https://www.kernel.org/doc/Documentation/cgroup-v1/blkio-controller.txt