zfs-dkms rpm: simplify scriptlets, fix uninstall

Two problems led to unexpected behaviour of the scriptlets:

1) Newer DKMS versions change the formatting of "dkms status":

   (old) zfs, 2.1.2, 5.14.10-300.fc35.x86_64, x86_64: installed
   (new) zfs/2.1.2, 5.14.10-300.fc35.x86_64, x86_64: installed

   Which broke a conditional determining whether to uninstall.

2) zfs_config.h not packaged properly, but was attempted to be read
   in the %preun scriptlet:

   CONFIG_H="/var/lib/dkms/zfs/2.1.2/*/*/zfs_config.h"

   Which broke the uninstallation of the module, which left behind a
   dangling symlink, which broke DKMS entirely with this error:

     Error! Could not locate dkms.conf file.
     File: /var/lib/dkms/zfs/2.1.1/source/dkms.conf does not exist.

This change attempts to simplify life by:

*  Avoiding parsing anything (less prone to future breakage)
*  Uses %posttrans instead of %post for module installation, because
   %post happens before %preun, while %posttrans happens afterwards
*  Unconditionally reinstall module on upgrade, which is less
   efficient but the trade-off is that it's more reliable

Alternative approaches could involve fixing the existing parsing bugs
or improving the logic, but this comes at the cost of complexity and
possible future bugs.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Jeremy Visser <jeremyvisser@google.com>
Closes #10463
Closes #13182

rpm/generic/zfs-dkms.spec.in

@@ -68,46 +68,9 @@ fi
 %defattr(-,root,root)
 /usr/src/%{module}-%{version}
 
-%post
-for POSTINST in /usr/lib/dkms/common.postinst; do
-    if [ -f $POSTINST ]; then
-        $POSTINST %{module} %{version}
-        exit $?
-    fi
-    echo "WARNING: $POSTINST does not exist."
-done
-echo -e "ERROR: DKMS version is too old and %{module} was not"
-echo -e "built with legacy DKMS support."
-echo -e "You must either rebuild %{module} with legacy postinst"
-echo -e "support or upgrade DKMS to a more current version."
-exit 1
-
 %preun
-# Are we doing an upgrade?
+dkms remove -m %{module} -v %{version} --all
-if [ "$1" = "1" -o "$1" = "upgrade" ] ; then
+
-	# Yes we are.  Are we upgrading to a new ZFS version?
+%posttrans
-	NEWEST_VER=$(dkms status zfs | tr -d , | sort -r -V | awk '/installed/{print $2; exit}')
+/usr/lib/dkms/common.postinst %{module} %{version}
-	if [ "$NEWEST_VER" != "%{version}" ] ; then
-		# Yes, it's a new ZFS version.  We'll uninstall the old module
-		# later on in this script.
-		true
-	else
-		# No, it's probably an upgrade of the same ZFS version
-		# to a new distro (zfs-dkms-0.7.12.fc28->zfs-dkms-0.7.12.fc29).
-		# Don't remove our modules, since the rebuild for the new
-		# distro will automatically delete the old modules.
-		exit 0
-	fi
-fi
 
-# If we're here then we're doing an uninstall (not upgrade).
-CONFIG_H="/var/lib/dkms/%{module}/%{version}/*/*/%{module}_config.h"
-SPEC_META_ALIAS="@PACKAGE@-@VERSION@-@RELEASE@"
-DKMS_META_ALIAS=`cat $CONFIG_H 2>/dev/null |
-    awk -F'"' '/META_ALIAS\s+"/ { print $2; exit 0 }'`
-if [ "$SPEC_META_ALIAS" = "$DKMS_META_ALIAS" ]; then
-    echo -e
-    echo -e "Uninstall of %{module} module ($SPEC_META_ALIAS) beginning:"
-    dkms remove -m %{module} -v %{version} --all %{!?not_rpm:--rpm_safe_upgrade}
-fi
-exit 0