Using DKMS to maintain driver modules

In my prior post, I noted that maintaining custom drivers for the the kernel in RHEL and CentOS hosts can be a bit painful (and prone to leaving you with an unreachable or even unbootable system). One way to take some of the pain out of owning a system with custom drivers is to leverage DKMS. In general, DKMS is the recommended way to ensure that, as kernels are updated, required kernel modules are also (automatically) updated.

Unfortunately, use of the DKMS method will require that developer tools (i.e., the GNU C-compiler) be present on the system - either in perpetuity or just any time kernel updates are applied. It is very likely that your security team will object to - or even prohibit - this. If the objection/prohibition cannot be overridden, use of the DKMS method will not be possible.

Steps

1. Set an appropriate version string into the shell-environment:
   

   export VERSION=3.2.2

2. Make sure that appropriate header files for the running-kernel are installed
   

   yum install -y kernel-devel-$(uname -r)

3. Ensure that the dkms utilities are installed:
   

   yum --enablerepo=epel install dkms

4. Download the driver sources and unarchive into the /usr/src directory:
   

   wget https://sourceforge.net/projects/e1000/files/ixgbevf%20stable/${VERSION}/ixgbevf-${VERSION}.tar.gz/download \
       -O /tmp/ixgbevf-${VERSION}.tar.gz && \
      ( cd /usr/src && \
         tar zxf /tmp/ixgbevf-${VERSION}.tar.gz )

5. Create an appropriate DKMS configuration file for the driver:
   

   cat > /usr/src/ixgbevf-${VERSION}/dkms.conf << EOF
   PACKAGE_NAME="ixgbevf"
   PACKAGE_VERSION="${VERSION}"
   CLEAN="cd src/; make clean"
   MAKE="cd src/; make BUILD_KERNEL=\${kernelver}"
   BUILT_MODULE_LOCATION[0]="src/"
   BUILT_MODULE_NAME[0]="ixgbevf"
   DEST_MODULE_LOCATION[0]="/updates"
   DEST_MODULE_NAME[0]="ixgbevf"
   AUTOINSTALL="yes"
   EOF

6. Register the module to the DKMS-managed kernel tree:
   

   dkms add -m ixgbevf -v ${VERSION}

7. Build the module against the currently-running kernel:
   

   dkms build ixgbevf/${VERSION}

Verification

The easiest way to verify the correct functioning of DKMS is to:

1. Perform a `yum update -y`
2. Check that the new drivers were created by executing `find /lib/modules -name ixgbevf.ko`. Output should be similar to the following:
   

   find /lib/modules -name ixgbevf.ko | grep extra
   /lib/modules/2.6.32-642.1.1.el6.x86_64/extra/ixgbevf.ko
   /lib/modules/2.6.32-642.6.1.el6.x86_64/extra/ixgbevf.ko

   There should be at least two output-lines: one for the currently-running kernel and one for the kernel update. If more kernels are installed, there may be more than just two output-lines
    
   
3. Reboot the system, then check what version is active:
   

   modinfo ixgbevf | grep extra
   filename:       /lib/modules/2.6.32-642.1.1.el6.x86_64/extra/ixgbevf.ko

   If the output is null, DKMS didn't build the new module.