While debugging why adding a systemd-tmpfiles configuration file to link /var/lib/mpd into /var/volatile/lib was not working, I discovered that meta-rcar-gen3 has modifications to the default fstab (with a base-files recipe bbappend) and patches systemd to change systemd-tmpfiles behavior.  AFAICT from the commit messages the goal appears to be to enable using NFS root without the no_root_squash option.  In practice, it seems to break the actually expected systemd-tmpfiles behavior, as /var/volatile ends up owned by nobody.nogroup with permissions of drwxrwxrwxt and systemd-tmpfiles throws the unsafe transition error for any attempt to create subdirectories/files with explicit ownership underneath /var/volatile.

I propose masking out these changes from the rcar3 BSP on the following grounds:

• AGL upstream does not support using NFS root by default (and does not test it).
• Changing systemd-tmpfiles default behavior violates the principle of least surprise, and seems quite a bit less than ideal for a BSP layer unless there is some form of documented on/off switch, which this currently does not have.
• Patching core packages like base-files and systemd in a BSP layer is quite a bit less than ideal for AGL, as it hurts shared state reuse across aarch64 based builds.

Input from harunobu.kurokawa, ronan, and sdesneux on whether there needs to be an attempt made at allowing the changes in the BSP to be enabled at the expense of potentially breaking with the agl-demo-platform image would be appreciated.