[Cake] Testing and build IDs

[Toke Høiland-Jørgensen]

For those of you building your own Cake modules for testing:

The Cake build now supports embedding the git hash of the source
repository into the kernel module, which makes it possible to refer back
to the source version from the test results. The latest git version of
Flent will pick this up if pointed at the right box (with
--remote-metadata=HOSTNAME).

For normal builds this should work out of the box. For openwrt, support
went into trunk last Friday to allow the right debug symbol to be
embedded in the .ko. However, by default openwrt doesn't build the
kernel with the configuration parameter that makes it export the value;
you need to enable CONFIG_KERNEL_KALLSYMS which is called "Compile the
kernel with symbol table information" under "Global build settings" in
menuconfig.

In the interest of actually keeping track of the different versions when
comparing test results, I'll encourage those of you who do your own
builds to include this option and to collect this metadata along with
the test results. The latter is as easy as supplying Flent with
--remote-metadata=root at router.ip.addr after setting up a suitable public
key :)

Cheers,

-Toke