Fix ownership of VM files of unprivileged builds

mkfs needs to see the files it copies into the fs as owned by root.
Otherwise the whole fs tree would be owned by the calling user. Doesn't
matter too much when setting up the build root initially as rpm is
called inside anyway to fix everything. However, when reusing an image
suddenly all ownerships would change.

build-vm

@@ -460,6 +460,12 @@ vm_img_mkfs() {
     if test -n "$populate"; then
       if test "$fs" = "ext2" -o "$fs" = "ext3" -o "$fs" = "ext4"; then
         mkfs_extra_options="$mkfs_extra_options -d $populate"
+        # mkfs needs to see the files it copies into the fs as owned by root.
+        # Otherwise the whole fs tree would be owned by the calling user.
+        # Doesn't matter too much when setting up the build root initially as
+        # rpm is called inside anway to fix everything. However, when reusing
+        # an image suddenly all ownerships would change.
+        [ -x "/usr/bin/unshare" ] && mkfs="unshare --user --map-root-user $mkfs"
       else
         print "ERROR: populating filesystem is only supported with ext file systems"
         cleanup_and_exit 1