Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR_ALL features on upper device

From: Eric Dumazet <edumazet@google.com>
To: Tariq Toukan <ttoukan.linux@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Tariq Toukan <tariqt@nvidia.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
	Moshe Shemesh <moshe@nvidia.com>,
	Maxim Mikityanskiy <maximmi@nvidia.com>,
	Saeed Mahameed <saeedm@nvidia.com>
Subject: Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR_ALL features on upper device
Date: Wed, 25 Nov 2020 10:27:28 +0100	[thread overview]
Message-ID: <CANn89iLTsTgW9UPFn_LNN5Qvs9+0drfcW2cQHtCVYMoboHdv4Q@mail.gmail.com> (raw)
In-Reply-To: <329952c5-b208-1781-5604-2b408796ec90@gmail.com>

On Wed, Nov 25, 2020 at 10:06 AM Tariq Toukan <ttoukan.linux@gmail.com> wrote:
>
>
>
> On 11/25/2020 5:25 AM, Herbert Xu wrote:
> > On Tue, Nov 24, 2020 at 11:48:35AM +0100, Eric Dumazet wrote:
> >>
> >> Well, the 'increment' part was suggesting the function was adding
> >> flags, not removing them.
> >
> > The idea of the increment part is that we're adding a constituent
> > device, not that we're adding features.  There have always been
> > features which were conjunctions, i.e., they must be supported by
> > all underlying devices for them to be enabled on the virtual device.
> >
> > Your use of the increment function is unusual, as you're not adding
> > features that belong to one underlying device, but rather you're
> > trying to enable a feature on the virtual device unconditionally.

This was not the intent.

We can still disable TSO on the bonding device if desired.

pk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
tcp-segmentation-offload; done
tcp-segmentation-offload: on
tcp-segmentation-offload: on
tcp-segmentation-offload: on
lpk51:~# ethtool -K bond0 tso off
Actual changes:
tcp-segmentation-offload: off
tx-tcp-segmentation: off
tx-tcp-ecn-segmentation: off
tx-tcp-mangleid-segmentation: off
tx-tcp6-segmentation: off
large-receive-offload: off [requested on]
lpk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
tcp-segmentation-offload; done
tcp-segmentation-offload: off
tcp-segmentation-offload: on
tcp-segmentation-offload: on

The intent was that we could have :

lpk51:~# ethtool -K bond0 tso on
Actual changes:
tcp-segmentation-offload: on
tx-tcp-segmentation: on
tx-tcp-ecn-segmentation: on
tx-tcp-mangleid-segmentation: on
tx-tcp6-segmentation: on
lpk51:~# ethtool -K eth1 tso off
lpk51:~# ethtool -K eth2 tso off
lpk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
tcp-segmentation-offload; done
tcp-segmentation-offload: on
tcp-segmentation-offload: off
tcp-segmentation-offload: off
lpk51:~#

> >
> >> We might ask Herbert Xu if we :
> >>
> >> 1) Need to comment the function, or change its name to be more descriptive.
> >> 2) Change the behavior (as you suggested)
> >> 3) Other choice.
> >
> > I think Tariq's patch is fine, although a comment should be added
> > to netdev_add_tso_features as this use of the increment function
> > is nonstandard.
> >
>
> Thanks Herbert, I'll add a comment and re-spin.

I think we should remove the use of  netdev_increment_features() and
replace it with something else,
because there is too much confusion.