Merge pull request #523 from networkop/cvx-docs-deps

fix and docs for ignite directories and deps

docs/manual/kinds/cvx.md

@@ -11,9 +11,13 @@ CVX nodes launched with containerlab comes up with:
 
 CVX supports two modes of operation:
 
-* Using Firecracker micro-VMs -- this mode runs Cumulus VX inside a micro-VM on top of the native Cumulus kernel. This is the default way of running CVX nodes.
+* Using Firecracker micro-VMs -- this mode runs Cumulus VX inside a micro-VM on top of the native Cumulus kernel. This is mode uses `ignite` runtime and is the default way of running CVX nodes.
 * Using only the container runtime -- this mode runs Cumulus VX container image directly inside the container runtime (e.g. Docker). Due to the lack of Cumulus VX kernel modules, some features are not supported, most notable one being MLAG. In order to use this mode add `runtime: docker` under the cvx node definition (see also [this example](https://github.com/srl-labs/containerlab/blob/master/lab-examples/cvx02/topo.clab.yml)).
 
+!!! note
+    When running in the default `ignite` runtime mode, the only host OS dependency is `/dev/kvm`[^1] required to support harware-assisted virtualisation. Firecracker VMs are spun up inside a special "sandbox" container that has all the right tools and dependencies required to run micro-VMs.
+
+    Additionally, containerlab creates a number of directories under `/var/lib/firecracker` for nodes running in `ignite` runtime to store runtime metadata; these directories are managed by containerlab.
 
 ## Managing cvx nodes
 Cumulus VX node launched with containerlab can be managed via the following interfaces:
@@ -69,4 +73,6 @@ The following labs feature CVX node:
 
 ## Known issues or limitations
 
-* CVX in Ignite is always attached to the default docker bridge network
+* CVX in Ignite is always attached to the default docker bridge network
+
+[^1]: this device is already part of the linux kernel, therefore this can be read as "no external dependencies are needed for running cvx with `ignite` runtime.

runtime/ignite/iginite.go

@@ -72,7 +72,9 @@ func (c *IgniteRuntime) Init(opts ...runtime.RuntimeOption) error {
 	// ensure firecracker directroy
 	for _, path := range runtimePaths {
 		if _, err := os.Stat(path); os.IsNotExist(err) {
-			os.Mkdir(path, os.ModeDir)
+			if err := os.MkdirAll(path, os.ModeDir); err != nil {
+				return fmt.Errorf("cannot create the required directory %q: %s", path, err)
+			}
 		}
 	}