ell 0.31 fails to build with pre-4.12 kernel headers

Hello,

Since commit fa950995a48bbcd8f0d3dfbbe9a7f768aba5c50f ("genl: enable extended error messages"), ell makes use of the extended ACK reporting mechanism added by Linux commit 2d4bc93368f5a0ddb57c8c885cdad9c9b7a10ed5.

Due to this, the build of ell 0.31 fails when the toolchain uses kernel headers older than Linux 4.12, as NLM_F_ACK_TLVS and NETLINK_EXT_ACK are not defined.

See an example build failure:

http://autobuild.buildroot.net/results/baf/bafc0ee2a3bcb2418a3612da38eb9dcd586b57d4/build-end.log

It would probably be good to make this feature optional in ell, based on some configure.ac checks of the availability of extended ACK reporting.

Thanks!

Thomas

Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com