Switch to 'mapped' access mode for hostfs

Passthrough mode only works as expected when running as root. On
Debian/Ubuntu systems qemu runs as user 'libvirt-qemu' and group 'kvm'
so all shared files must be chowned to grant access from guests.

Symlinks created on the host are still problematic because the Plan 9
filesystem has no direct notion of symbolic links, see [1].

[1] - http://ericvh.github.com/9p-rfc/rfc9p2000.u.html

testing/scripts/build-guestkernel

@@ -10,7 +10,6 @@ echo "Building guest kernel version $KERNELVERSION"
 
 check_commands bunzip2 bzcat make wget
 
-mkdir -p $BUILDDIR
 cd $BUILDDIR
 
 if [ ! -f "$KERNELTARBALL" ]

testing/scripts/build-rootimage

@@ -28,7 +28,7 @@ check_commands partprobe qemu-img qemu-nbd
 load_qemu_nbd
 
 mkdir -p $LOOPDIR
-mkdir -p $ROOTIMGCOMPILEDIR
+mkdir -p $SHAREDDIR/compile
 mkdir -p $IMGDIR
 
 log_action "Creating root image $ROOTIMG"
@@ -47,24 +47,21 @@ log_action "Mounting proc filesystem to $LOOPDIR/proc"
 execute "mount -t proc none $LOOPDIR/proc"
 do_on_exit umount $LOOPDIR/proc
 
-mkdir -p $LOOPDIR/root/compile
-log_action "Mounting $ROOTIMGCOMPILEDIR as /root/compile"
-execute "mount -o bind $ROOTIMGCOMPILEDIR $LOOPDIR/root/compile"
-do_on_exit rm -r $LOOPDIR/root/compile
-do_on_exit umount $LOOPDIR/root/compile
+mkdir -p $LOOPDIR/root/shared
+log_action "Mounting $SHAREDDIR as /root/shared"
+execute "mount -o bind $SHAREDDIR $LOOPDIR/root/shared"
+do_on_exit umount $LOOPDIR/root/shared
 
 echo "Installing software from source"
 RECPDIR=$DIR/recipes
 RECIPES=`ls $RECPDIR/*.mk | xargs -n1 basename`
-execute "cp -r $RECPDIR/patches $LOOPDIR/root/compile" 0
+execute "cp -r $RECPDIR/patches $LOOPDIR/root/shared/compile" 0
 for r in $RECIPES
 do
-	cp $RECPDIR/$r ${LOOPDIR}/root/compile
+	cp $RECPDIR/$r ${LOOPDIR}/root/shared/compile
 	log_action "Installing from recipe $r"
-	execute_chroot "make SWANVERSION=$SWANVERSION -C /root/compile -f $r"
+	execute_chroot "make SWANVERSION=$SWANVERSION -C /root/shared/compile -f $r"
 done
 
 log_action "Removing /etc/resolv.conf"
 execute "rm -f $LOOPDIR/etc/resolv.conf"
-
-mkdir -p $LOOPDIR/hostfs