Allow elements to add drivers to dracut

It is reasonable that elements may need to include additional
kernel modules in a dracut ramdisk.  This is done with the
--add-drivers option to dracut, but previously the value passed
was hard-coded.

This change allows an element to put a file containing its desired
drivers in a dracut-drivers.d directory, and the list there will
be added to the list of drivers added.  This functions in
essentially the same way as the binary-deps.d directory that
already exists for including additional executables in a ramdisk.

Change-Id: Ie892b908d36c175a469f7cde7dd803ad4b1942b6

elements/dracut-ramdisk/README.rst

@@ -6,3 +6,15 @@ Build Dracut-based ramdisks
 This is an alternative to the `ramdisk` element that uses
 Dracut to provide the base system functionality instead of
 Busybox.
+
+For elements that need additional drivers in the ramdisk image,
+a dracut-drivers.d feature is included that works in a similar
+fashion to the binary-deps.d feature.  The element needing to
+add drivers should create a dracut-drivers.d directory and
+populate it with a single file listing all of the kernel modules
+it needs added to the ramdisk.  Comments are not supported in this
+file.  Note that these modules must be installed in the chroot first.
+
+By default, the virtio, virtio_net, and virtio_blk modules are
+included so that ramdisks are able to function properly in a
+virtualized environment.

elements/dracut-ramdisk/dracut-drivers.d/base-drivers

@@ -0,0 +1,3 @@
+virtio
+virtio_net
+virtio_blk

elements/dracut-ramdisk/post-install.d/01-ensure-drivers

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+set -eu
+set -o pipefail
+
+if [ ${DIB_DEBUG_TRACE:-1} -gt 0 ]; then
+    set -x
+fi
+
+TARGET_DIR="/tmp/in_target.d/"
+
+EXTRA_DRIVERS=
+
+for _FILE in $(ls ${TARGET_DIR}/dracut-drivers.d/) ; do
+    _FILE="${TARGET_DIR}/dracut-drivers.d/${_FILE}"
+    if [ -s $_FILE ]; then
+        for _LINE in $(cat $_FILE) ; do
+            EXTRA_DRIVERS="${EXTRA_DRIVERS} $_LINE"
+        done
+    fi
+done
+
+if [ "$EXTRA_DRIVERS" = "" ]; then
+    echo "No extra drivers found"
+else
+    DRIVERS_OUTPUT="/etc/dib_dracut_drivers"
+    echo "Creating extra drivers record at: ${DRIVERS_OUTPUT}"
+    echo "$EXTRA_DRIVERS" >${DRIVERS_OUTPUT}
+fi

elements/dracut-ramdisk/post-install.d/99-build-dracut-ramdisk

@@ -66,7 +66,7 @@ dracut -N \
     --kernel-cmdline "rd.shell rd.debug rd.neednet=1 rd.driver.pre=ahci" \
     --include "$TMP_MOUNT_PATH/" / \
     --kver "${KERNEL_VERSION}" \
-    --add-drivers "virtio virtio_net virtio_blk" \
+    --add-drivers "$(cat /etc/dib_dracut_drivers)" \
     -o "dash plymouth" \
     /tmp/ramdisk