initramfs: add support for root.img with partition table

Installing grub on root.img require some space before the filesystem.
Create it by adding partition table to root.img. This commit take care
of assembling dmroot device when such partition table is present, while
preserving compatibility with partition-less images.

QubesOS/qubes-issues#2577

dracut/full-dmroot/qubes_cow_setup.sh

@@ -56,14 +56,21 @@ log_begin "Waiting for /dev/xvda* devices..."
 while ! [ -e /dev/xvda ]; do sleep 0.1; done
 log_end
 
+# prefer first partition if exists
+if [ -b /dev/xvda1 ]; then
+    ROOT_DEV=xvda1
+else
+    ROOT_DEV=xvda
+fi
+
 SWAP_SIZE=$(( 1024 * 1024 * 2 )) # sectors, 1GB
 
-if [ `cat /sys/block/xvda/ro` = 1 ] ; then
+if [ `cat /sys/class/block/$ROOT_DEV/ro` = 1 ] ; then
     log_begin "Qubes: Doing COW setup for AppVM..."
 
     while ! [ -e /dev/xvdc ]; do sleep 0.1; done
-    VOLATILE_SIZE=$(cat /sys/block/xvdc/size) # sectors
-    ROOT_SIZE=$(cat /sys/block/xvda/size) # sectors
+    VOLATILE_SIZE=$(cat /sys/class/block/xvdc/size) # sectors
+    ROOT_SIZE=$(cat /sys/class/block/$ROOT_DEV/size) # sectors
     if [ $VOLATILE_SIZE -lt $SWAP_SIZE ]; then
         die "volatile.img smaller than 1GB, cannot continue"
     fi
@@ -78,7 +85,7 @@ EOF
     mkswap /dev/xvdc1
     while ! [ -e /dev/xvdc2 ]; do sleep 0.1; done
 
-    echo "0 `cat /sys/block/xvda/size` snapshot /dev/xvda /dev/xvdc2 N 16" | \
+    echo "0 `cat /sys/class/block/$ROOT_DEV/size` snapshot /dev/$ROOT_DEV /dev/xvdc2 N 16" | \
         dmsetup --noudevsync create dmroot || die "Qubes: FATAL: cannot create dmroot!"
     log_end
 else
@@ -92,8 +99,17 @@ EOF
     fi
     while ! [ -e /dev/xvdc1 ]; do sleep 0.1; done
     mkswap /dev/xvdc1
-    echo "0 `cat /sys/block/xvda/size` linear /dev/xvda 0" | \
-        dmsetup --noudevsync create dmroot || die "Qubes: FATAL: cannot create dmroot!"
+    if [ "$ROOT_DEV" = "xvda1" ]; then
+        # grub2-probe for some reason can't parse dm-linear pointing at
+        # partition device directly, but can when it points at it indirectly
+        # through base device and offset; lets make life easier for users of
+        # grub2-install
+        DM_ROOT="/dev/xvda $(cat /sys/class/block/$ROOT_DEV/start)"
+    else
+        DM_ROOT="/dev/$ROOT_DEV 0"
+    fi
+    echo "0 `cat /sys/class/block/$ROOT_DEV/size` linear $DM_ROOT" | \
+        dmsetup create dmroot || { echo "Qubes: FATAL: cannot create dmroot!"; exit 1; }
     log_end
 fi
 dmsetup mknodes dmroot

dracut/simple/init.sh

@@ -20,14 +20,21 @@ die() {
 echo "Waiting for /dev/xvda* devices..."
 while ! [ -e /dev/xvda ]; do sleep 0.1; done
 
+# prefer first partition if exists
+if [ -b /dev/xvda1 ]; then
+    ROOT_DEV=xvda1
+else
+    ROOT_DEV=xvda
+fi
+
 SWAP_SIZE=$(( 1024 * 1024 * 2 )) # sectors, 1GB
 
-if [ `cat /sys/block/xvda/ro` = 1 ] ; then
+if [ `cat /sys/class/block/$ROOT_DEV/ro` = 1 ] ; then
     echo "Qubes: Doing COW setup for AppVM..."
 
     while ! [ -e /dev/xvdc ]; do sleep 0.1; done
-    VOLATILE_SIZE=$(cat /sys/block/xvdc/size) # sectors
-    ROOT_SIZE=$(cat /sys/block/xvda/size) # sectors
+    VOLATILE_SIZE=$(cat /sys/class/block/xvdc/size) # sectors
+    ROOT_SIZE=$(cat /sys/class/block/$ROOT_DEV/size) # sectors
     if [ $VOLATILE_SIZE -lt $SWAP_SIZE ]; then
         die "volatile.img smaller than 1GB, cannot continue"
     fi
@@ -43,7 +50,7 @@ EOF
     mkswap /dev/xvdc1
     while ! [ -e /dev/xvdc2 ]; do sleep 0.1; done
 
-    echo "0 `cat /sys/block/xvda/size` snapshot /dev/xvda /dev/xvdc2 N 16" | \
+    echo "0 `cat /sys/class/block/$ROOT_DEV/size` snapshot /dev/$ROOT_DEV /dev/xvdc2 N 16" | \
         dmsetup create dmroot || { echo "Qubes: FATAL: cannot create dmroot!"; exit 1; }
     echo Qubes: done.
 else
@@ -57,7 +64,16 @@ EOF
     fi
     while ! [ -e /dev/xvdc1 ]; do sleep 0.1; done
     mkswap /dev/xvdc1
-    echo "0 `cat /sys/block/xvda/size` linear /dev/xvda 0" | \
+    if [ "$ROOT_DEV" = "xvda1" ]; then
+        # grub2-probe for some reason can't parse dm-linear pointing at
+        # partition device directly, but can when it points at it indirectly
+        # through base device and offset; lets make life easier for users of
+        # grub2-install
+        DM_ROOT="/dev/xvda $(cat /sys/class/block/$ROOT_DEV/start)"
+    else
+        DM_ROOT="/dev/$ROOT_DEV 0"
+    fi
+    echo "0 `cat /sys/class/block/$ROOT_DEV/size` linear $DM_ROOT" | \
         dmsetup create dmroot || { echo "Qubes: FATAL: cannot create dmroot!"; exit 1; }
     echo Qubes: done.
 fi