On Sun, Dec 27, 2020 at 12:34:09PM +0800, Bruce LIU wrote: > Hi Michal Kubecek and Network dev team, > > Good day! Hope you are doing well. > This is Bruce from China, and please allow me to cc Rudy from Cisco Systems > in China team. > > We are facing a weird behavior about "master-slave configuration" function > in ethtool. > Please correct me if I am wrong.... > > As you know, start from ethtool 5.8, "master/slave configuration support" > added. > https://lwn.net/Articles/828044/ > > ======================================================================== > Appeal: > Confirm and discuss workaround > > ======================================================================== > Issue description: > As we test in lab, no "master-slave" option supported. > > ======================================================================== > Issue reproduce: > root@raspberrypi:~# ethtool -s eth0 master-slave master-preferred > ethtool: bad command line argument(s) > For more information run ethtool -h > > ======================================================================== > Environment: > debian-live-10.7.0-amd64-standard.iso > Kernel 5.4.79
This is the problem. Kernel support for this feature was added in 5.8-rc1 so that your kernel does not have it and there is no chance it could possibly work. Newer ethtool has support for this feature but kernel must support it as well for it to actually work. But I agree that the error message is misleading. We handle subcommands supported only in netlink with proper error message when ioctl fallback is used but we don't do the same for new parameters of existing subcommands which are generally supported by ioctl code. That's why the command line parser used by ioctl code does not recognize the new parameter and handles it as a syntax error. We'll need to handle new parameters in ioctl parser so that it produces more meaningful error for parameters only supported via netlink. Long term, the proper solution would probably be using one parser for both netlink and ioctl but that was something I wanted to avoid for now to reduce the risk of introducing subtle changes in behaviour of existing code. Michal
