Extract the symlink-to-bpf-linker logic from integration-test to xtask
and use it in a new build script in integration-ebpf, causing ebpf
probes to be rebuilt when bpf-linker changes. Previously bpf-linker
changes would rebuild integration-test, but not integration-ebpf,
resulting in stale tests.
Note that this still doesn't address the possibility that a new
bpf-linker is added to the PATH ahead of the cached one. Solving this in
the general case would require rebuild-if-changed-env=PATH *and*
rebuild-if-changed={every-directory-in-PATH} which would likely mean far
too much cache invalidation.
Libbpf is used by xtasks, in the command, ensure that the submodules
are initialized. This eases the user-experience so that users don't
need to think about the submodule, while retaining all the benefits
of using a submodule vs forcing the user to manually check out libbpf
and stick it in some pre-defined place.
We use the symbol pointing to libbpf in xtask in the build script
to avoid repeating this constant.
Also, we install git in the vm so that we can init the submodule
when we build in the vm.
Tamir Duberstein
Andrew Werner