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.
In a "merged-usr" system, `/lib` is a symlink to `/usr/lib`. When
installing *sys-apps/systemd*, Portage checks to ensure this is the
case. If this happens after `make modules_install` is run, `/lib` is
a directory, which causes the installation to fail. To avoid this, we
need to explicitly install the modules into `/usr/lib` so that the
symlink can be created later.
Building the OS is now as simple as running `make` on a Gentoo system.
Interestingly, when `make` is executed as a (grand)child process of
another `make` process, it always prints an `Entering directory ...`
message. This breaks the `make kernelversion` command, by adding
extraneous text to the output.
Dustin