providers/qemu: fix default to fwcfg

[laenion]

Commit 3b930b made it impossible to build Ignition on any other arch then s390x, ppc64le, amd64 or arm64 by explicitly stating the allowed platforms. This made it impossible to build e.g. for 386.

Continue to use the fw_cfg interface as default instead.

[jlebon]

Thanks! Was actually looking at the best way to approach this too. :)

I think this is fine, though I was thinking the opposite of this, i.e. use the blockdev provider on everything but where we know qemu_fw_cfg is supported. AFAIK, that's only amd64, 386, and aarch64. WDYT?

(On that topic, note that Fedora at least stopped building 32-bit x86 kernels in recent releases. But no reason not to keep supporting it upstream.)

[coreosbot]

Can one of the admins verify this patch?

[laenion]

According to https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg (first sentence) there should be several more platforms supporting qemu_fs_cfg, but that list obviously isn't complete (amd64 is missing for example), and I don't have access to all possible platforms. Due to that I'm also not sure which version is better - I also wouldn't mind inverting the logic. In theory one would have to check all the platforms listed on https://github.com/golang/go/blob/master/src/go/build/syslist.go...

Sorry for not seeing the discussion in the other ticket by the way, I would have attached myself there.

[jlebon]

OK sure, given that qemu_fw_cfg has been the long-standing default, and that #905 was specifically called out as an experiment for s390x and ppc64le, let's keep that the default.

Though my hope is that we end up using the same mechanism across all architectures eventually (see #928). But let's not rush that process.

[jlebon]

LGTM!

[jlebon]

Can we change the commit title to something like: providers/qemu: fix default to fwcfg ?

[laenion]

Sure, just a minute.

[bgilbert]

ok to test

[bgilbert]

Thanks for the fix!