Activate LVM volume groups before looking for zpools.

Original-patch-by: @jgoerzen
Signed-off-by: Benjamin Albrecht <git@albrecht.io>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/pkg-zfs#102
Closes #4029

contrib/initramfs/scripts/local-top/zfs

@@ -0,0 +1,60 @@
+#!/bin/sh
+PREREQ="mdadm mdrun multipath"
+
+prereqs()
+{
+        echo "$PREREQ"
+}
+
+case $1 in
+# get pre-requisites
+prereqs)
+        prereqs
+        exit 0
+        ;;
+esac
+
+
+#
+# Helper functions
+#
+message()
+{
+        if [ -x /bin/plymouth ] && plymouth --ping; then
+                plymouth message --text="$@"
+        else
+                echo "$@" >&2
+        fi
+        return 0
+}
+
+udev_settle()
+{
+        # Wait for udev to be ready, see https://launchpad.net/bugs/85640
+        if [ -x /sbin/udevadm ]; then
+                /sbin/udevadm settle --timeout=30
+        elif [ -x /sbin/udevsettle ]; then
+                /sbin/udevsettle --timeout=30
+        fi
+        return 0
+}
+
+
+activate_vg()
+{
+        # Sanity checks
+        if [ ! -x /sbin/lvm ]; then
+                message "lvm is not available"
+                return 1
+        fi
+
+        # Detect and activate available volume groups
+        /sbin/lvm vgscan
+        /sbin/lvm vgchange -a y --sysinit
+        return $?
+}
+
+udev_settle
+activate_vg
+
+exit 0