Fix in-tree module dependency docs

The docs incorrectly said /lib/modules is mounted into build pods - it's
only mounted into worker pods. Added the missing COPY instruction that
users need to make depmod work at build time.

Additionally removing usr mount volume from worker pod.

Author: TomerNewman

docs/mkdocs/documentation/kmod_image.md

@@ -24,6 +24,8 @@ This is especially useful if your kmod image contains several kernel modules and
 another.
 To generate dependencies and map files for a specific kernel version, run `depmod -b /opt ${KERNEL_FULL_VERSION}`.
 
+If you use a multi-stage Dockerfile, run `depmod` at the end of the last stage.
+
 ## Example `Dockerfile`
 
 The example below builds a test kernel module from the KMM repository.
@@ -172,16 +174,15 @@ RUN depmod -b /opt ${KERNEL_FULL_VERSION}
 ### Depending on in-tree kernel modules
 
 Some kernel modules depend on other kernel modules shipped with the node's distribution.
-To avoid copying those dependencies into the kmod image, KMM mounts `/usr/lib/modules` into both the build and the
-worker Pod's filesystems.  
-By creating a symlink from `/opt/usr/lib/modules/[kernel-version]/[symlink-name]` to
-`/usr/lib/modules/[kernel-version]`, `depmod` can use the in-tree kmods on the building node's filesystem to resolve
-dependencies.
+To avoid copying those dependencies into the kmod image, KMM mounts `/lib/modules` directories of the host into the
+worker Pod's filesystem.  
+By creating a symlink from `/opt/lib/modules/[kernel-version]/[symlink-name]` to
+`/lib/modules/[kernel-version]`, `depmod` can resolve dependencies using in-tree modules from the DTK image at build time.
 At runtime, the worker Pod extracts the entire image, including the `[symlink-name]` symbolic link.
-That link points to `/usr/lib/modules/[kernel-version]` in the worker Pod, which is mounted from the node's filesystem.
+That link points to `/lib/modules/[kernel-version]` in the worker Pod, which is mounted from the node's filesystem.
 `modprobe` can then follow that link and load the in-tree dependencies as needed.
 
-In the example below, we use `host` as the symbolic link name under `/opt/usr/lib/modules/[kernel-version]`:
+In the example below, we use `host` as the symbolic link name under `/opt/lib/modules/[kernel-version]`:
 
 ```dockerfile
 ARG DTK_AUTO
@@ -198,6 +199,8 @@ ARG KERNEL_FULL_VERSION
 
 RUN dnf update && dnf install -y kmod
 
+COPY --from=builder /lib/modules/${KERNEL_FULL_VERSION} /lib/modules/${KERNEL_FULL_VERSION}
+
 COPY --from=builder /usr/src/kernel-module-management/ci/kmm-kmod/kmm_ci_a.ko /opt/lib/modules/${KERNEL_FULL_VERSION}/
 COPY --from=builder /usr/src/kernel-module-management/ci/kmm-kmod/kmm_ci_b.ko /opt/lib/modules/${KERNEL_FULL_VERSION}/
 
@@ -208,8 +211,7 @@ RUN depmod -b /opt ${KERNEL_FULL_VERSION}
 ```
 
 !!! warning
-    `depmod` will generate dependency files based on the kernel modules present on the node that runs the kmod image
-    build.  
+    `depmod` will generate dependency files based on the kernel modules present in the DTK image used during the build.  
     On the node on which KMM loads the kernel modules, `modprobe` will expect the files to be present under
-    `/usr/lib/modules/[kernel-version]`, and the same filesystem layout.  
+    `/lib/modules/[kernel-version]`, and the same filesystem layout.  
     It is highly recommended that the build and the target nodes share the same distribution and release.

internal/pod/workerpodmanager.go

@@ -332,8 +332,7 @@ func (wpmi *workerPodManagerImpl) baseWorkerPod(ctx context.Context, nmc client.
 	moduleConfig *kmmv1beta1.ModuleConfig) (*v1.Pod, error) {
 
 	const (
-		volNameLibModules    = "lib-modules"
-		volNameUsrLibModules = "usr-lib-modules"
+		volNameLibModules = "lib-modules"
 	)
 
 	hostPathDirectory := v1.HostPathDirectory
@@ -363,15 +362,6 @@ func (wpmi *workerPodManagerImpl) baseWorkerPod(ctx context.Context, nmc client.
 				},
 			},
 		},
-		{
-			Name: volNameUsrLibModules,
-			VolumeSource: v1.VolumeSource{
-				HostPath: &v1.HostPathVolumeSource{
-					Path: "/usr/lib/modules",
-					Type: &hostPathDirectory,
-				},
-			},
-		},
 		{
 			Name: volNameTmp,
 			VolumeSource: v1.VolumeSource{
@@ -391,11 +381,6 @@ func (wpmi *workerPodManagerImpl) baseWorkerPod(ctx context.Context, nmc client.
 			MountPath: "/lib/modules",
 			ReadOnly:  true,
 		},
-		{
-			Name:      volNameUsrLibModules,
-			MountPath: "/usr/lib/modules",
-			ReadOnly:  true,
-		},
 		{
 			Name:      volNameTmp,
 			MountPath: sharedFilesDir,

internal/pod/workerpodmanager_test.go

@@ -433,7 +433,6 @@ func getBaseWorkerPod(subcommand string, owner ctrlclient.Object, firmwareHostPa
 
 	const (
 		volNameLibModules     = "lib-modules"
-		volNameUsrLibModules  = "usr-lib-modules"
 		volNameVarLibFirmware = "lib-firmware"
 	)
 
@@ -551,11 +550,6 @@ cp -R /firmware-path/* /tmp/firmware-path;
 							MountPath: "/lib/modules",
 							ReadOnly:  true,
 						},
-						{
-							Name:      volNameUsrLibModules,
-							MountPath: "/usr/lib/modules",
-							ReadOnly:  true,
-						},
 						{
 							Name:      volNameTmp,
 							MountPath: sharedFilesDir,
@@ -597,15 +591,6 @@ cp -R /firmware-path/* /tmp/firmware-path;
 						},
 					},
 				},
-				{
-					Name: volNameUsrLibModules,
-					VolumeSource: v1.VolumeSource{
-						HostPath: &v1.HostPathVolumeSource{
-							Path: "/usr/lib/modules",
-							Type: &hostPathDirectory,
-						},
-					},
-				},
 				{
 					Name: volNameTmp,
 					VolumeSource: v1.VolumeSource{