Message-ID: <92f578b7-347e-22c7-be83-cae4dce101f6@blackwall.org>
Date:   Mon, 11 Apr 2022 21:31:22 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Roopa Prabhu <roopa@...dia.com>, netdev@...r.kernel.org
Cc:     idosch@...sch.org, kuba@...nel.org, davem@...emloft.net,
        bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v2 0/8] net: bridge: add flush filtering support

On 11/04/2022 21:18, Nikolay Aleksandrov wrote:
> 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

that's the only thing, overloading delneigh with a flush-behaviour (multi-del or whatever)
would require to push the mac check to ndo_fdb_del implementers

I don't mind going that road if others agree that we should do it through delneigh
+ a bit/option to signal flush, instead of a new rtm type.

> 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.

scratch the specific attributes, those can be adapted for both cases

> 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
> 
> 

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