Re: [PATCH net] net/8021q: Check the correct vlan filter capability

[Saeed Mahameed <saeedm@dev.mellanox.co.il>]

On Wed, Feb 24, 2016 at 10:27 PM, Saeed Mahameed
<saeedm@dev.mellanox.co.il> wrote:
>>> Netdev features can be changed dynamically to off after vlan_vid_add
>>> was called, thus vlan_vid_del will skip ndo_vlan_rx_kill_vid and will
>>> leave the device driver with un-freed resources.
>>
>> Are you sure the fix isn't to make vlan_vid_add() check ->features instead
>> of ->hw_features.
>
> This is exactly what this fix suggests, "->features" is not consistent
> and can be turned ON/OFF between vlan_add/del which can leave the NIC
> driver in inconsistent state !
>
>>
>> Should we really be trying to add VLAN filters when the user has
>> turned it off?
>
> Well, I think it is debatable, but the current implementation is not
> consistent, especially for adding vlan 0 by default and then the user
> disables the vlan filter, this will cause the stack to never call the
> nic ndo_vlan_rx_kill_vid for the pre added vlan 0 and vise versa call
> kill_vid without add_vid, BUG ?
>
> So i think we have two options, use this patch, and always trust to
> delegate vlan_vid_add/del to the NIC when it's HW supports it, and the
> nic will be smart enough to know what to do with it (in case vlan
> filter is enabled/disabled). Or, for each vlan we can remember if it
> was added to the NIC or not so the stack will know whether to clean it
> up or not.

BTW we choose the first option since the "buggy" function is called
"vlan_hw_filter_capable" which lead us to decide that the function
should be looking for ->hw_features and not ->features.
and i think this way it makes more sense.