vm-initramfs: use sysfs directly to get block device parameters

Don't use blkdev program, as isn't installed by default by dracut in FC17.
Actually it isn't necessary to get 'ro' and 'size' parameters, as they can be
read directly from sysfs.

vm-initramfs/lib/dracut/hooks/pre-udev/90_qubes_cow_setup.sh

@@ -14,18 +14,18 @@ modprobe xenblk || modprobe xen-blkfront || echo "Qubes: Cannot load Xen Block F
 echo "Waiting for /dev/xvda* devices..."
 while ! [ -e /dev/xvda ]; do sleep 0.1; done
 
-if [ `blockdev --getro /dev/xvda` = 1 ] ; then
+if [ `cat /sys/block/xvda/ro` = 1 ] ; then
 	echo "Qubes: Doing COW setup for AppVM..."
 
 	while ! [ -e /dev/xvdc ]; do sleep 0.1; done
 	while ! [ -e /dev/xvdc2 ]; do sleep 0.1; done
 
-	echo "0 `blockdev --getsz /dev/xvda` snapshot /dev/xvda /dev/xvdc2 N 16" | \
+	echo "0 `cat /sys/block/xvda/size` snapshot /dev/xvda /dev/xvdc2 N 16" | \
     		dmsetup create dmroot || { echo "Qubes: FATAL: cannot create dmroot!"; }
 	echo Qubes: done.
 else
 	echo "Qubes: Doing R/W setup for TemplateVM..."
-	echo "0 `blockdev --getsz /dev/xvda` linear /dev/xvda 0" | \
+	echo "0 `cat /sys/block/xvda/size` linear /dev/xvda 0" | \
     		dmsetup create dmroot || { echo "Qubes: FATAL: cannot create dmroot!"; exit 1; }
 	echo Qubes: done.
 fi