netdev - Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent locked port feature

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Date:   Thu, 2 Jun 2022 12:33:34 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Hans Schultz <schultz.hans@...il.com>,
        Ido Schimmel <idosch@...dia.com>
Cc:     Ido Schimmel <idosch@...sch.org>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>, Shuah Khan <shuah@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org, bridge@...ts.linux-foundation.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH V3 net-next 1/4] net: bridge: add fdb flag to extent
 locked port feature

On 02/06/2022 12:17, Hans Schultz wrote:
> On tis, maj 31, 2022 at 17:23, Ido Schimmel <idosch@...dia.com> wrote:
>> On Tue, May 31, 2022 at 11:34:21AM +0200, Hans Schultz wrote:
>>>> Just to give you another data point about how this works in other
>>>> devices, I can say that at least in Spectrum this works a bit
>>>> differently. Packets that ingress via a locked port and incur an FDB
>>>> miss are trapped to the CPU where they should be injected into the Rx
>>>> path so that the bridge will create the 'locked' FDB entry and notify it
>>>> to user space. The packets are obviously rated limited as the CPU cannot
>>>> handle billions of packets per second, unlike the ASIC. The limit is not
>>>> per bridge port (or even per bridge), but instead global to the entire
>>>> device.
>>>
>>> Btw, will the bridge not create a SWITCHDEV_FDB_ADD_TO_DEVICE event
>>> towards the switchcore in the scheme you mention and thus add an entry
>>> that opens up for the specified mac address?
>>
>> It will, but the driver needs to ignore FDB entries that are notified
>> with locked flag. I see that you extended 'struct
>> switchdev_notifier_fdb_info' with the locked flag, but it's not
>> initialized in br_switchdev_fdb_populate(). Can you add it in the next
>> version?
> 
> An issue with sending the flag to the driver is that port_fdb_add() is
> suddenly getting more and more arguments and getting messy in my
> opinion, but maybe that's just how it is...
> 
> Another issue is that
> bridge fdb add MAC dev DEV master static
> seems to add the entry with the SELF flag set, which I don't think is
> what we would want it to do or?

I don't see such thing (hacked iproute2 to print the flags before cmd):
$ bridge fdb add 00:11:22:33:44:55 dev vnet110 master static
flags 0x4

0x4 = NTF_MASTER only

> Also the replace command is not really supported properly as it is. I
> have made a fix for that which looks something like this:
> 
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 6cbb27e3b976..f43aa204f375 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -917,6 +917,9 @@ static int fdb_add_entry(struct net_bridge *br, struct net_bridge_port *source,
>                 if (flags & NLM_F_EXCL)
>                         return -EEXIST;
>  
> +               if (flags & NLM_F_REPLACE)
> +                       modified = true;
> +
>                 if (READ_ONCE(fdb->dst) != source) {
>                         WRITE_ONCE(fdb->dst, source);
>                         modified = true;
> 
> The argument for always sending notifications to the driver in the case
> of replace is that a replace command will refresh the entries timeout if
> the entry is the same. Any thoughts on this?

I don't think so. It always updates its "used" timer, not its "updated" timer which is the one
for expire. A replace that doesn't actually change anything on the entry shouldn't generate
a notification.