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Updating documentation around kernel modules

Combined DKMS documentation with this since they're directly related.
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1 parent ccce5e5 commit 247d3f582252ba1776170d7893d05d0978cff907 KillerSpaz committed Dec 16, 2016
Showing with 122 additions and 42 deletions.
  1. +1 −0 .gitignore
  2. +0 −29 docs/os/configuration/dkms/index.md
  3. +121 −13 docs/os/configuration/loading-kernel-modules/index.md
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__pycache__
/.dapper
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+.idea
@@ -1,29 +0,0 @@
----
-title: DKMS
-layout: os-default
-
----
-
-## DKMS
-
-DKMS is supported by running the DKMS scripts inside a container. To compile any kernel modules, you first need to [install the kernel headers]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/). After kernel headers are enabled, they are installed in `/lib/modules/$(uname -r)/build`. To deploy containers that runs DKMS, you will need to ensure that you bind mount in `/usr/src` and `/lib/modules`.
-
-### Docker Example
-
-```
-# Installing Kernel Headers for Docker
-$ sudo ros service enable kernel-headers
-$ sudo ros service up kernel-headers
-# Run a container in Docker and bind mount specific directories to run DKMS
-$ docker run -it -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu:15.10 sh -c 'apt-get update && apt-get install -y sysdig-dkms'
-```
-
-### System Docker Example
-
-```
-# Installing Kernel Headers for System Docker
-$ sudo ros service enable kernel-headers-system-docker
-$ sudo ros service up kernel-headers-system-docker
-# Run a container in System Docker and bind mount specific directories to run DKMS
-$ sudo system-docker run -it -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu:15.10 sh -c 'apt-get update && apt-get install -y sysdig-dkms'
-```
@@ -1,32 +1,140 @@
---
-title: Loading Kernel Modules in RancherOS
+title: DKMS / Loadable Kernel Modules in RancherOS
layout: os-default
---
-## Loading Kernel Modules
----
+## Dynamic Kernel Module Support (DKMS) / Loadable Kernel Modules (LKM)
-Kernel modules can be automatically loaded with the `rancher.modules` cloud-config field.
+To compile any Kernel Modules, you first need to [deploy the Kernel Headers]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/).
-```yaml
-#cloud-config
-rancher:
- modules: [btrfs]
-```
+### DKMS
-This functionality is also available via a kernel parameter. For example, the btrfs module could be automatically loaded with `rancher.modules=[btrfs]` as a kernel parameter.
+DKMS is supported by running the DKMS scripts inside a *privileged* container.
+
+> To deploy containers that compiles DKMS modules, you will need to ensure that you bind-mount `/usr/src` and `/lib/modules`.
+
+> To deploy containers that run any DKMS operations (i.e., `modprobe`), you will need to ensure that you bind-mount `/lib/modules`.
+
+By default, the `/lib/modules` folder is already available in the console deployed via [RancherOS System Services]({{site.baseurl}}/os/system-services/built-in-system-services/), but not `/usr/src`. You will likely need to [deploy your own container](#docker-example) for compilation purposes.
-### Loading Kernel Modules via a System Service
+To learn more about Docker's privileged mode, or to limit capabilities, please review the [Docker Runtime privilege and Linux capabilities documentation](https://docs.docker.com/engine/reference/run/#/runtime-privilege-and-linux-capabilities).
-Privileged containers can load kernel modules. In RancherOS, the kernel modules are in the standard `/lib/modules/$(uname -r)` folder. If you want to be able to run `modprobe` from a container, you will need to bind mount the `/lib/modules` into your container.
+#### cloud-config Example
```yaml
myservice:
image: ...
privileged: true
volumes:
- /lib/modules:/lib/modules
+ - /usr/src:/usr/src
```
-By default, the `/lib/modules` folder is already available in the console.
+#### Docker Example
+
+> For one-off operations, it's useful to use `--rm` to clean up containers when operations complete.
+
+```bash
+$ sudo system-docker run -it --rm --name dkms-install -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu sh -c 'apt-get update && apt-get install -y sysdig-dkms'
+```
+
+The same approach can be utilized with the User Docker Daemon, just replace `sudo system-docker` with `docker`.
+
+### LKM Dependencies
+
+In some situations, another Kernel Module might need loading prior to any module you're trying to add.
+
+In this example, we'll reference the `v4l2loopback` DKMS module, which requires probing `videodev` into the Kernel space and is not on any filesystem by default.
+
+First, you must enable `kernel-extras`, then `modprobe` your dependencies and subsequent modules:
+
+```bash
+sudo ros service enable kernel-extras
+sudo ros service up -d kernel-extras
+```
+
+This will overlay all the compiled modules into `/lib/modules/$(uname -r)` that are configured in the default RancherOS Kernel config.
+
+Now you are ready to add your Modules into the Kernel space:
+
+```bash
+sudo modprobe videodev
+sudo modprobe v4l2loopback
+```
+
+To see which modules are pre-built, you can either do a listing of all `.ko` (kernel object) files, or review the Kernel config:
+
+```bash
+find /lib*/modules/$(uname -r) -name *.ko | less
+#or
+zcat /proc/config.gz | less
+```
+
+For more information regarding modifying the Kernel, please review the [Custom Kernels]({{site.baseurl}}/os/custom-builds/custom-kernels/) documentation.
+
+### Auto-Loading Modules
+
+Kernel Modules can be automatically loaded with the `rancher.modules` cloud-config field.
+
+```yaml
+#cloud-config
+rancher:
+ modules: [btrfs]
+```
+
+This functionality is also available via a kernel parameter. For example, the btrfs module could be automatically loaded with `rancher.modules=[btrfs]` as a kernel parameter.
+
+### Ubuntu-based Kernel Manipulation
+
+For images that are or derive from Ubuntu, you will need some small packages for `depmod`(`kmod`) and `modprobe`(`module-init-tools`):
+
+```bash
+sudo apt-get install kmod module-init-tools
+```
+
+Most packages should already list these as dependencies in Aptitude, as well as `gcc` and related libs for packages that require compilation (which is most).
+
+### Troubleshooting
+
+Messing around with the Kernel can be tricky, so here's some common issues:
+
+#### kernel source for this kernel does not seem to be installed.
+
+Simply put, the Kernel Headers (or Source) cannot be found; enable them via the [Kernel Headers System Service]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/).
+
+#### Operation not Permitted
+
+When inside a container, you might see similar to the following:
+```
+modprobe: ERROR: could not insert 'videodev': Operation not permitted
+```
+
+This is in reference to your container's privileges, not your user (i.e., `sudo` will not fix this).
+
+Instead, ensure you started the container with `--privileged` or the `cloud-config` setting described above.
+
+#### modprobe: ERROR: could not insert 'v4l2loopback': Unknown symbol in module, or unknown parameter (see dmesg)
+
+Again, using `v4l2loopback` as an example, but this can happen for any module.
+
+As stated, check out `dmesg` to see what the issue is. Chances are you'll see something like the following:
+
+```bash
+[ 322.734052] v4l2loopback: module verification failed: signature and/or required key missing - tainting kernel
+[ 322.734141] v4l2loopback: Unknown symbol video_ioctl2 (err 0)
+[ 322.734454] v4l2loopback: Unknown symbol v4l2_ctrl_handler_init_class (err 0)
+[ 322.734526] v4l2loopback: Unknown symbol video_devdata (err 0)
+[ 322.734563] v4l2loopback: Unknown symbol v4l2_ctrl_new_custom (err 0)
+[ 322.734599] v4l2loopback: Unknown symbol video_unregister_device (err 0)
+[ 322.734635] v4l2loopback: Unknown symbol video_device_alloc (err 0)
+[ 322.734696] v4l2loopback: Unknown symbol v4l2_device_register (err 0)
+[ 322.734732] v4l2loopback: Unknown symbol __video_register_device (err 0)
+[ 322.734765] v4l2loopback: Unknown symbol v4l2_ctrl_handler_free (err 0)
+[ 322.734796] v4l2loopback: Unknown symbol v4l2_device_unregister (err 0)
+[ 322.734828] v4l2loopback: Unknown symbol video_device_release (err 0)
+```
+
+This one can be trickier to evaluate, so start searching Google for symbol names to figure out which modules they derive from.
+
+In this example, `video_ioctl2` comes from `videodev` and can be simply inserted via the `kernel-extras` overlay described above.

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