Commits on Oct 11, 2023

1. Use 'unbuild' instead of 'remove' in kernel prerm script …

   When DKMS is invoked by the kernel_prerm.d_dkms script to remove modules
   from a kernel that is being removed, it uses the DKMS 'remove' command.
   If there are no other installations of the module, it will be removed
   completely from DKMS.  That seems to be an undesirable side-effect and
   predates the introduction of the DKMS 'unbuild' command which merely
   undoes the 'install' and 'build' steps.
   
   Change the script to use 'unbuild' instead of 'remove'.  Keep the echoed
   message that says "dkms: removing: ..." because "dkms: unbuilding: ..."
   may be confusing to the user.
   
   I have tested it by removing a kernel with a module installed by DKMS
   that was the only installed instance of the module.  Without the change,
   the module was removed completely from DKMS.  With the change, the
   module was removed from the kernel, but was not removed completely.  On
   reinstalling the kernel, the module was rebuilt and reinstalled for the
   kernel by DKMS.
   
   This change was suggested by @RalfGoebel for issue dell#37 and might be
   Debian-specific.
   
   For Debian and Ubuntu, the 'kernel_postinst.d_dkms' script is installed as
   '/etc/kernel/postinst.d/dkms' and '/etc/kernel/header_postinst.d/dkms',
   and the 'kernel_prerm.d_dkms' script is installed as
   '/etc/kernel/prerm.d/dkms'.  The scripts are invoked in the following
   circumstances, with the script parameter $1 set to the kernel version
   from the kernel package (referred to as "${KVER}" below):
   
   1. When a "linux-headers-${KVER}" package is installed (containing the
      stuff needed to build external modules), the
      '/etc/kernel/header_postinst.d/dkms' ('kernel_postinst.d_dkms')
      script is invoked to autoinstall DKMS modules for the kernel version,
      building the modules if necessary.
   
   2. When a "linux-image-${KVER}" package is installed (containing the
      Linux kernel binary, and in the case of Debian, also the kernel
      module binaries), the '/etc/kernel/postinst.d/dkms
      ('kernel_postinst.d_dkms') script is invoked to autoinstall DKMS
      modules for the kernel version, building the modules if necessary and
      possible.  (Building the modules will fail unless the
      "linux-headers-${KVER}" package is installed.)
   
   3. When a "linux-headers-${KVER}" package is being removed, none of the
      DKMS scripts are invoked.
   
   4. When a "linux-image-${KVER}" package is being removed, the
      '/etc/kernel/prerm.d/dkms' ('kernel_prerm.d_dkms') script is invoked
      to perform some sort of uninstallation action on all DKMS modules
      that have been built for the kernel version.  Prior to this patch,
      the DKMS 'remove' command was used to uninstall the modules.  This
      patch changes that to the DKMS 'unbuild' command which is less
      destructive.
   
   On first glance, it may seem better to use the DKMS 'uninstall' command
   when removing a "linux-image-${KVER}" package, and to use the DKMS
   'unbuild' command  when removing a "linux-headers-${KVER}" package.
   However, the "linux-image-${KVER}" and "linux-headers-${KVER}" packages
   do not depend on each other, so unbuilding the DKMS modules when the
   "linux-headers-${KVER}" package is being removed would have the side
   effect of uninstalling the DKMS modules for the kernel, even if the
   "linux-image-${KVER}" package is still installed.  Therefore, the
   compromise is to use the DKMS 'unbuild' command when removing a
   "linux-image-${KVER}" package and to do nothing when removing a
   "linux-headers-${KVER}" package.  This helps avoid littering the
   '/var/lib/dkms' directory with stale builds.  It is sub-optimal if the
   same version of the "linux-image-${KVER}" package is to be reinstalled
   later because the DKMS modules would need to be built again, but that
   should be fairly rare.  Normally, kernel packages are upgraded to a
   different version, requiring the DKMS modules to be built anyway.
   
   The script only affects DKMS modules with the "installed" status.  Only
   DKMS modules with the "installed" status have files in
   "/lib/modules/${KVER}" that need to be cleaned up.  It could be argued
   that since the script is using the DKMS 'unbuild' command, it should
   also unbuild DKMS modules with the "built" status.  There must have been
   some external intervention outside of the kernel installation/removal
   hook scripts to leave those modules at the "built" status, so the script
   may be playing it safe by leaving those DKMS modules alone.
   
   Link: dell#37 (comment)
   Tested-by: Ian Abbott <[email protected]>
   Signed-off-by: Ian Abbott <[email protected]>

   

   ian-abbott committed Oct 11, 2023
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