Enable LVM autoextend and set default value to 90 for thin_pool

Fixes QubesOS/qubes-issues#5826

rpm_spec/core-dom0-linux.spec.in

@@ -192,6 +192,28 @@ if [ $1 -ge 2 ]; then
     fi
 fi
 
+# setup thinpool autoextend
+if [ -e /etc/lvm/lvm.conf ]; then
+    tpool_threshold_line_value=$(grep -n -Po '^[^#]thin_pool_autoextend_threshold[ \t]*=[ \t]*\K\d+' /etc/lvm/lvm.conf)
+    if [ -n "$tpool_threshold_line_value" ]; then
+        tpool_threshold_line="$(echo "$tpool_threshold_line_value" | cut -d':' -f1)"
+        tpool_threshold_value="$(echo "$tpool_threshold_line_value" | cut -d':' -f2)"
+
+        prev_line="$(sed -n "$((tpool_threshold_line-1))p" /etc/lvm/lvm.conf)"
+        qubes_comment='# QUBES OS: Custom value detected, not enforcing default. Recommended value: 90'
+
+        if [ "$tpool_threshold_value" == 100 ]; then
+            sed -i 's|^\([^#]thin_pool_autoextend_threshold\)[ \t]*=.*|\1 = 90|' /etc/lvm/lvm.conf
+
+            systemctl restart lvm2-monitor
+        else
+            if [ "$tpool_threshold_value" != 90 ] && [ "$prev_line" != "$qubes_comment" ]; then
+                sed -i "${tpool_threshold_line}i $qubes_comment" /etc/lvm/lvm.conf
+            fi
+        fi
+    fi
+fi
+
 %preun
 if [ "$1" = 0 ] ; then
 	# no more packages left