Gentoo ebuild for LVM2 prior to 2.02.63-r1 doesn't install rules:

10-dm.rules
  11-dm-lvm.rules
  13-dm-disk.rules
  95-dm-notify.rules

but provides only 64-device-mapper.rules combining more or less the
above rules files.

modules.d/90dm/module-setup.sh

@@ -22,5 +22,8 @@ install() {
 
     type -P dmeventd >/dev/null && dracut_install dmeventd
     inst_rules 10-dm.rules 95-dm-notify.rules
+    # Gentoo ebuild for LVM2 prior to 2.02.63-r1 doesn't install above rules
+    # files, but provides the one below:
+    inst_rules 64-device-mapper.rules
 }
 

modules.d/90dmraid/module-setup.sh

@@ -43,6 +43,9 @@ install() {
     done
 
     inst_rules 10-dm.rules 13-dm-disk.rules 95-dm-notify.rules 
+    # Gentoo ebuild for LVM2 prior to 2.02.63-r1 doesn't install above rules
+    # files, but provides the one below:
+    inst_rules 64-device-mapper.rules
 
     inst "$moddir/dmraid.sh" /sbin/dmraid_scan
 

modules.d/90lvm/module-setup.sh

@@ -47,6 +47,9 @@ install() {
     fi
 
     inst_rules 10-dm.rules 13-dm-disk.rules 95-dm-notify.rules 11-dm-lvm.rules
+    # Gentoo ebuild for LVM2 prior to 2.02.63-r1 doesn't install above rules
+    # files, but provides the one below:
+    inst_rules 64-device-mapper.rules
 
     inst "$moddir/lvm_scan.sh" /sbin/lvm_scan
     inst_hook cmdline 30 "$moddir/parse-lvm.sh"