This can be seen as a subproject of ethtool netlink interface but from the technical view it's independent.

Every new piece of software is going to be buggy and with frequent changes and rewrites, new regressions are introduced. Automated selftests can help a lot but as ethtool deals with hardware devices, we do not want these tests to depend on a specific hardware. The netdevsim driver was created as a virtual device which (unlike e.g. dummy) cannot be used for actual network traffic but implements various configuration interfaces so that it can be used for their (automated) testing.

Currently (February 2020, before Hackweek 19), netdevsim driver does not provide ethtool_ops callbacks so that it cannot be used with ethtool.

The goal is to implement at least basic ethtool_ops callbacks so that netdevsim can be used for automated testing of both kernel ethtool code and userspace ethtool utility. Ideally, use could set internal values used for replies so that various corner cases can be also tested.