[yocto] [meta-selinux] Dependency loop help with selinux userspace/python3/util-linux

["Peter Morrow" <peter.morrow@microsoft.com>]

Hi Folks,

I'm trying to upgrade the meta-selinux layer to use a newer version of
the selinux userspace tools (from 2.8 to 2.9), in doing so these newer
userspace tools now depend on python3 instead of python2.  This
unfortunately has created a build time dependency loop in yocto:

python3 --> util-linux --> libselinux --> python3 (used to be python2
with 2.8 selinux userspace).

Running "bitbake libselinux" results in a pile of loops, the one below
illustrates the point.

ERROR:
Dependency loop #1 found:
  Task /workspace/git/yocto-selinux/meta-selinux/recipes-
security/selinux/libselinux_2.9.bb:do_package (dependent Tasks ['gcc-
runtime_9.2.bb:do_packagedata', 'libsepol_2.9.bb:do_packagedata',
'rpm_4.14.2.1.bb:do_populate_sysroot', 'glibc_2.30.bb:do_packagedata',
'python3_3.7.5.bb:do_packagedata', 'libpcre_8.43.bb:do_packagedata',
'pseudo_git.bb:do_populate_sysroot',
'dwarfsrcfiles.bb:do_populate_sysroot',
'libselinux_2.9.bb:do_install'])
  Task /workspace/git/yocto-selinux/meta-selinux/recipes-
security/selinux/libselinux_2.9.bb:do_packagedata (dependent Tasks
['libselinux_2.9.bb:do_package'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-
extended/pam/libpam_1.3.1.bb:do_package (dependent Tasks ['gcc-
runtime_9.2.bb:do_packagedata', 'rpm_4.14.2.1.bb:do_populate_sysroot',
'glibc_2.30.bb:do_packagedata', 'libselinux_2.9.bb:do_packagedata',
'flex_2.6.0.bb:do_packagedata', 'pseudo_git.bb:do_populate_sysroot',
'libxcrypt_4.4.8.bb:do_packagedata', 'libpam_1.3.1.bb:do_install',
'dwarfsrcfiles.bb:do_populate_sysroot',
'cracklib_2.9.5.bb:do_packagedata', 'libtool-
cross_2.4.6.bb:do_packagedata'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-
extended/pam/libpam_1.3.1.bb:do_packagedata (dependent Tasks
['libpam_1.3.1.bb:do_package'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-core/util-
linux/util-linux_2.34.bb:do_package (dependent Tasks ['gcc-
runtime_9.2.bb:do_packagedata', 'rpm_4.14.2.1.bb:do_populate_sysroot',
'bash-completion_2.9.bb:do_packagedata',
'zlib_1.2.11.bb:do_packagedata', 'glibc_2.30.bb:do_packagedata',
'libselinux_2.9.bb:do_packagedata',
'pseudo_git.bb:do_populate_sysroot',
'ncurses_6.1+20190803.bb:do_packagedata',
'libxcrypt_4.4.8.bb:do_packagedata', 'libcap-
ng_0.7.9.bb:do_packagedata', 'opkg-utils_0.4.1.bb:do_packagedata',
'libpam_1.3.1.bb:do_packagedata', 'util-
linux_2.34.bb:do_install_ptest_base',
'dwarfsrcfiles.bb:do_populate_sysroot', 'util-
linux_2.34.bb:do_install', 'libtool-cross_2.4.6.bb:do_packagedata'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-core/util-
linux/util-linux_2.34.bb:do_packagedata (dependent Tasks ['util-
linux_2.34.bb:do_package'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-
devtools/python/python3_3.7.5.bb:do_package (dependent Tasks
['xz_5.2.4.bb:do_packagedata', 'bzip2_1.0.8.bb:do_packagedata',
'gdbm_1.18.1.bb:do_packagedata', 'libnsl2_git.bb:do_packagedata', 'gcc-
runtime_9.2.bb:do_packagedata', 'rpm_4.14.2.1.bb:do_populate_sysroot',
'python3_3.7.5.bb:do_install', 'libffi_3.3~rc0.bb:do_packagedata',
'pseudo_git.bb:do_populate_sysroot',
'sqlite3_3.29.0.bb:do_packagedata', 'openssl_1.1.1d.bb:do_packagedata',
'libtirpc_1.1.4.bb:do_packagedata', 'zlib_1.2.11.bb:do_packagedata',
'glibc_2.30.bb:do_packagedata', 'libxcrypt_4.4.8.bb:do_packagedata',
'python3_3.7.5.bb:do_install_ptest_base', 'util-
linux_2.34.bb:do_packagedata', 'opkg-utils_0.4.1.bb:do_packagedata',
'readline_8.0.bb:do_packagedata',
'dwarfsrcfiles.bb:do_populate_sysroot', 'libtool-
cross_2.4.6.bb:do_packagedata'])
  Task /workspace/git/yocto-selinux/poky/meta/recipes-
devtools/python/python3_3.7.5.bb:do_packagedata (dependent Tasks
['python3_3.7.5.bb:do_package'])

Python3 (3.7.5) appears to depend on util-linux for libuuid support, so
I don't think anything can be done with regards to this.  libselinux
now depends on python3 as of 2.9, so again not much can be done here. 
It's proving a bit harder to track down the util-linux dependency on
libselinux but I believe this is a hard depdency as well.

I'm using the master branch of both poky and meta-selinux for testing,
my local.conf file has the following to enable testing:

DISTRO_FEATURES_append=" acl xattr pam selinux"

The crux of the libselinux recipe change is really just changing the
python2 deps over to python3 ones in meta-selinux/recipes-
security/selinux/libselinux.inc.

At this point I'd be trying to look for places where recipes can be
split out to remove the loop, but nothing jumps out at me.

Can anyone offer any advice or pointers on how to get around this?  Or
am I just stuffed?

Many Thanks,
Peter.