netdev - Re: [PATCH 0/5] staging: fsl-dpaa2/ethsw: add the .ndo_fdb

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Message-ID: <VI1PR0402MB28000AEB0C3AE6E45AC2AAC8E0DC0@VI1PR0402MB2800.eurprd04.prod.outlook.com>
Date:   Tue, 30 Jul 2019 09:13:01 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>
Subject: Re: [PATCH 0/5] staging: fsl-dpaa2/ethsw: add the .ndo_fdb_dump
 callback

On 7/29/19 7:35 PM, Andrew Lunn wrote:
> On Mon, Jul 29, 2019 at 07:11:47PM +0300, Ioana Ciornei wrote:
>> This patch set adds some features and small fixes in the
>> FDB table manipulation area.
>>
>> First of all, we implement the .ndo_fdb_dump netdev callback so that all
>> offloaded FDB entries, either static or learnt, are available to the user.
>> This is necessary because the DPAA2 switch does not emit interrupts when a
>> new FDB is learnt or deleted, thus we are not able to keep the software
>> bridge state and the HW in sync by calling the switchdev notifiers.
>>
>> The patch set also adds the .ndo_fdb_[add|del] callbacks in order to
>> facilitate adding FDB entries not associated with any master device.
>>
>> One interesting thing that I observed is that when adding an FDB entry
>> associated with a bridge (ie using the 'master' keywork appended to the
>> bridge command) and then dumping the FDB entries, there will be duplicates
>> of the same entry: one listed by the bridge device and one by the
>> driver's .ndo_fdb_dump).
>> It raises the question whether this is the expected behavior or not.
> 
> DSA devices are the same, they don't provide an interrupt when a new
> entry is added by the hardware. So we can have two entries, or just
> the SW bridge entry, or just the HW entry, depending on ageing.
>

This also happens when dealing with static entries (not just dynamic 
ones that can be affected by ageing). All in all, the basic actions of 
adding/deleting entries and then dumping them works. It was just a 
question about switchdev's architecture.


>> Another concern is regarding the correct/desired machanism for drivers to
>> signal errors back to switchdev on adding or deleting an FDB entry.
>> In the switchdev documentation, there is a TODO in the place of this topic.
> 
> It used to be a two state prepare/commit transaction, but that was
> changed a while back.
> 
> Maybe the DSA core code can give you ideas?
>

I looked in the DSA core before sending these patches out and it's doing 
the exact same thing as ethsw - even though it notifies switchdev if the 
entry could be offloaded (ie no error) all entries will still be present 
in the 'bridge fdb' output. In the SWITCHDEV_FDB_DEL_TO_DEVICE case, it 
seems that it just closes the netdev without any further action.

On the other hand, the mlxsw_spectrum also calls the notifiers when an 
offloaded entry is deleted (on SWITCHDEV_FDB_DEL_TO_DEVICE). This seems 
like a reasonable thing to do, maybe in another patch set.

Ioana C