netdev - Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR

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Date:   Wed, 25 Nov 2020 10:27:28 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Tariq Toukan <ttoukan.linux@...il.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Tariq Toukan <tariqt@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Moshe Shemesh <moshe@...dia.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR_ALL
 features on upper device

On Wed, Nov 25, 2020 at 10:06 AM Tariq Toukan <ttoukan.linux@...il.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.