On Tue, 14 Nov 2017 10:30:33 -0800 Girish Moodalbail <girish.moodalb...@oracle.com> wrote:
> On 11/14/17 5:21 AM, Nicolas Dichtel wrote: > > With commits 35e015e1f577 and a2d3f3e33853, the global 'accept_dad' flag > > is also taken into account (default value is 1). If either global or > > per-interface flag is non-zero, DAD will be enabled on a given interface. > > > > This is not backward compatible: before those patches, the user could > > disable DAD just by setting the per-interface flag to 0. Now, the > > user instead needs to set both flags to 0 to actually disable DAD. > > > > Restore the previous behaviour by setting the default for the global > > 'accept_dad' flag to 0. This way, DAD is still enabled by default, > > as per-interface flags are set to 1 on device creation, but setting > > them to 0 is enough to disable DAD on a given interface. > > > > - Before 35e015e1f57a7 and a2d3f3e33853: > > global per-interface DAD enabled > > [default] 1 1 yes > > X 0 no > > X 1 yes > > > > - After 35e015e1f577 and a2d3f3e33853: > > global per-interface DAD enabled > > [default] 1 1 yes > > 0 0 no > > 0 1 yes > > 1 0 yes > > > > - After this fix: > > global per-interface DAD enabled > > 1 1 yes > > 0 0 no > > [default] 0 1 yes > > 1 0 yes > > Above table can be summarized to.. > > - After this fix: > global per-interface DAD enabled > 1 X yes > 0 0 no > [default] 0 1 yes > > So, if global is set to '1', then irrespective of what the per-interface > value > is DAD will be enabled. Is it not confusing. Shouldn't the more specific > value > override the general value? Might be a bit confusing, yes, but in order to implement an overriding mechanism you would need to implement a tristate option as Eric K. proposed. That is, by default you would have -1 (meaning "don't care") on per-interface flags, and if this value is changed then the per-interface value wins over the global one. Sensible, but I think it's outside of the scope of this patch, which is just intended to restore a specific pre-existing userspace expectation. > On the other hand, if the global is set to '0', then per-interface value will > be > honored (overrides global). So, the meaning of global varies based on its > value. > Isn't that confusing as well. I don't find this confusing though. Setting the global flag always has the meaning of "force enabling DAD on all interfaces". You would have the same problem if you chose a logical AND between global and per-interface flag. There, setting the global flag would mean "force disabling DAD on all interfaces". So the only indisputable improvement I see here would be to implement a "don't care" value (either for global or for per-interface flags). But I'd rather agree with Nicolas that we should fix a potentially broken userspace assumption first. -- Stefano
