Although Build Appliance VM can run using Virtual Box (see https://bugzilla.yoctoproject.org/show_bug.cgi?id=1971) adding support to allow installing Virtual Box guest additions would make possible many additional features such as cut/paste between host/guest, sharing folders,integrated cursor... While it is possible to build BA with the guest additions already built/included, that is not practical, as the additions may need to be rebuilt each time VirtualBox is updated. To support rebuilding of the guest additions, BA must contain kernel headers (and some additional files) allowing rebuilding Linux device drivers. The detailed steps to build the guest additions should be documented as well. (https://www.yoctoproject.org/documentation/build-appliance-manual)
Sent two patches to openembedded-core@lists.openembedded.org for review.
To proceed with this, https://bugzilla.yoctoproject.org/show_bug.cgi?id=7095 must be first resolved.
I succeeded to install VirtualBox additions in the Build Appliance. (This needed both kernel-dev and kernel-src in the Build Appliance image). I tested the additions by sharing a folder with the host. (poky 8cd1decf77fac7de076673bbd89b28aff526ac86). Will have a new recipe soon.
posted patch to the mailing list: http://lists.openembedded.org/pipermail/openembedded-core/2016-April/120054.html
Merged with master: https://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=faaeaf98c790c35c18fd9aadc8257634dc7a1597