When running inside a QEMU microvm with the source directory shared
via 9pfs, the kernel build process fails
> Error: Could not mmap file: vmlinux
Thus, we need to run the build in a path on a local filesystem. To
support this, the Makefile now supports an `O` option, and all the build
scripts have been adjusted to make use of it as needed.
Since building in a local filesystem would ultimately discard the final
artifacts when the VM terminates, we need yet a different location for
the files we want to keep. The `IMAGESDIR` option can be used to
specify this path. This path can be on a shared filesystem, thus
saving the artifacts outside the microvm.
Several packages end up with circular dependencies, depending on which
Portage profile is selected. The default profiles have a circular
dependency between *sys-libs/pam* and *sys-libs/libcap*. Systemd and
SELinux profiles have even more issues.
We can break the circular dependencies by explicitly building *libcap*
with`USE=-pam` first, which happens to be the default configuration
generated by `crossdev`. Then, we need to switch to a more complete
profile in order to build *glibc* and *util-linux*. At this point, the
build root should be complete enough to build anything without circular
dependencies.
Dustin