Re: [PATCH net-next v2 0/8] net: bridge: add flush filtering support

[Nikolay Aleksandrov <razor@blackwall.org>]

On 11/04/2022 21:08, Roopa Prabhu wrote:
> 
> On 4/11/22 10:29, Nikolay Aleksandrov wrote:
>> Hi,
>> This patch-set adds support to specify filtering conditions for a flush
>> operation. This version has entirely different entry point (v1 had
>> bridge-specific IFLA attribute, here I add new RTM_FLUSHNEIGH msg and
>> netdev ndo_fdb_flush op) so I'll give a new overview altogether.
>> After me and Ido discussed the feature offlist, we agreed that it would
>> be best to add a new generic RTM_FLUSHNEIGH with a new ndo_fdb_flush
>> callback which can be re-used for other drivers (e.g. vxlan).
>> Patch 01 adds the new RTM_FLUSHNEIGH type, patch 02 then adds the
>> new ndo_fdb_flush call. With this structure we need to add a generic
>> rtnl_fdb_flush which will be used to do basic attribute validation and
>> dispatch the call to the appropriate device based on the NTF_USE/MASTER
>> flags (patch 03). Patch 04 then adds some common flush attributes which
>> are used by the bridge and vxlan drivers (target ifindex, vlan id, ndm
>> flags/state masks) with basic attribute validation, further validation
>> can be done by the implementers of the ndo callback. Patch 05 adds a
>> minimal ndo_fdb_flush to the bridge driver, it uses the current
>> br_fdb_flush implementation to flush all entries similar to existing
>> calls. Patch 06 adds filtering support to the new bridge flush op which
>> supports target ifindex (port or bridge), vlan id and flags/state mask.
>> Patch 07 converts ndm state/flags and their masks to bridge-private flags
>> and fills them in the filter descriptor for matching. Finally patch 08
>> fills in the target ifindex (after validating it) and vlan id (already
>> validated by rtnl_fdb_flush) for matching. Flush filtering is needed
>> because user-space applications need a quick way to delete only a
>> specific set of entries, e.g. mlag implementations need a way to flush only
>> dynamic entries excluding externally learned ones or only externally
>> learned ones without static entries etc. Also apps usually want to target
>> only a specific vlan or port/vlan combination. The current 2 flush
>> operations (per port and bridge-wide) are not extensible and cannot
>> provide such filtering.
>>
>> I decided against embedding new attrs into the old flush attributes for
>> multiple reasons - proper error handling on unsupported attributes,
>> older kernels silently flushing all, need for a second mechanism to
>> signal that the attribute should be parsed (e.g. using boolopts),
>> special treatment for permanent entries.
>>
>> Examples:
>> $ bridge fdb flush dev bridge vlan 100 static
>> < flush all static entries on vlan 100 >
>> $ bridge fdb flush dev bridge vlan 1 dynamic
>> < flush all dynamic entries on vlan 1 >
>> $ bridge fdb flush dev bridge port ens16 vlan 1 dynamic
>> < flush all dynamic entries on port ens16 and vlan 1 >
>> $ bridge fdb flush dev ens16 vlan 1 dynamic master
>> < as above: flush all dynamic entries on port ens16 and vlan 1 >
>> $ bridge fdb flush dev bridge nooffloaded nopermanent self
>> < flush all non-offloaded and non-permanent entries >
>> $ bridge fdb flush dev bridge static noextern_learn
>> < flush all static entries which are not externally learned >
>> $ bridge fdb flush dev bridge permanent
>> < flush all permanent entries >
>> $ bridge fdb flush dev bridge port bridge permanent
>> < flush all permanent entries pointing to the bridge itself >
>>
>> Note that all flags have their negated version (static vs nostatic etc)
>> and there are some tricky cases to handle like "static" which in flag
>> terms means fdbs that have NUD_NOARP but *not* NUD_PERMANENT, so the
>> mask matches on both but we need only NUD_NOARP to be set. That's
>> because permanent entries have both set so we can't just match on
>> NUD_NOARP. Also note that this flush operation doesn't treat permanent
>> entries in a special way (fdb_delete vs fdb_delete_local), it will
>> delete them regardless if any port is using them. We can extend the api
>> with a flag to do that if needed in the future.
>>
>> Patch-sets (in order):
>>   - Initial flush infra and fdb flush filtering (this set)
>>   - iproute2 support
>>   - selftests
>>
>> Future work:
>>   - mdb flush support (RTM_FLUSHMDB type)
>>
>> Thanks to Ido for the great discussion and feedback while working on this.
>>
> Cant we pile this on to RTM_DELNEIGH with a flush flag ?.
> 
> It is a bulk del, and sounds seems similar to the bulk dev del discussion on netdev a few months ago (i dont remember how that api ended up to be. unless i am misremembering).
> 
> neigh subsystem also needs this, curious how this api will work there.
> 
> (apologies if you guys already discussed this, did not have time to look through all the comments)
> 
> 
> 

I thought about that option, but I didn't like overloading delneigh like that.
del currently requires a mac address and we need to either signal the device supports
a null mac, or we should push that verification to ndo_fdb_del users. Also we'll have
attributes which are flush-specific and will work only when flushing as opposed to when
deleting a specific mac, so handling them in the different cases can become a pain.
MDBs will need DELMDB to be modified in a similar way.

IMO a separate flush op is cleaner, but I don't have a strong preference.
This can very easily be adapted to delneigh with just a bit more mechanical changes
if the mac check is pushed to the ndo implementers.

FLUSHNEIGH can easily work for neighs, just need another address family rtnl_register
that implements it, the new ndo is just for PF_BRIDGE. :)

Cheers,
 Nik