On 11/14/17 11:10 AM, Stefano Brivio wrote:
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.
Agree.
Thanks,
~Girish
