Linux Ethernet Bridging - Apr 2023 - [Bridge] [PATCH v2 net-next 2/6] net: dsa: propagate flags down towards drivers

On Thu, Mar 30, 2023 at 04:54:19PM +0200, Hans Schultz
wrote:
> I don't know if you have a solution in mind wrt the behaviour of the
> offloaded flag if it is not to do as it does now and let the bridge age
> out dynamic entries. That led me to conclude that this patch-set cannot
> use the offloaded flag, but you seem to suggest otherwise.
> 
> If you have a suggestion, feel free.
Didn't I explain what I would do from the first reply on this thread?
https://patchwork.kernel.org/project/netdevbpf/patch/20230318141010.513424-3-netdev
at kapio-technology.com/#25270613

As a bug fix, stop reporting to switchdev those FDB entries with
BR_FDB_ADDED_BY_USER && !BR_FDB_STATIC. Then, after "net" is
merged into
"net-next" next Thursday (the ship has sailed for today), add
"bool static"
to the switchdev notifier info, and make all switchdev drivers (everywhere
where a SWITCHDEV_FDB_ADD_TO_DEVICE handler appears) ignore the
"added_by_user && !is_static" combination, but by their own
choice and
not by switchdev's choice.

Then, make DSA decide whether to handle the "added_by_user &&
!is_static"
combination or not, based on the presence of the DSA_FDB_FLAG_DYNAMIC
flag, which will be set in ds->supported_fdb_flags only for the mv88e6xxx
driver. When DSA_FDB_FLAG_DYNAMIC is not supported, DSA will not offload
the FDB entry: neither will it call port_fdb_add(), nor will it emit
SWITCHDEV_FDB_OFFLOADED. Ideally, it would also inform user space that
it can't offload this flag by returning an error, but the lack of an
error propagation mechanism from switchdev to the bridge FDB is a known
limitation which is hard to overcome, and is outside the scope of your
patchset I believe. To see whether DSA has acted upon the "master
dynamic"
flag or not, it would be good enough for the user to see something
adequate in "bridge fdb show | grep offloaded", I believe.

On Thu, Mar 30, 2023 at 18:07, Vladimir Oltean <olteanv at gmail.com>
wrote:
>
> Then, make DSA decide whether to handle the "added_by_user &&
!is_static"
> combination or not, based on the presence of the DSA_FDB_FLAG_DYNAMIC
> flag, which will be set in ds->supported_fdb_flags only for the
mv88e6xxx
> driver.
Okay, so this will require a new function in the DSA layer that sets
which flags are supported and that the driver will call on
initialization.

Where (in the DSA layer) should such a function be placed and what
should it be called?

On Thu, Mar 30, 2023 at 18:07, Vladimir Oltean <olteanv at gmail.com>
wrote:
> As a bug fix, stop reporting to switchdev those FDB entries with
> BR_FDB_ADDED_BY_USER && !BR_FDB_STATIC. Then, after "net"
is merged into
> "net-next" next Thursday (the ship has sailed for today), add
"bool static"
It is probably too late today (now I have a Debian based VM that can do
the selftests), but with this bug fix I have 1) not submitted bug fixes
before and 2) it probably needs an appropriate explanation, where I
don't know the problem well enough for general switchcores to submit
with a suitable text.