netdev - Re: [RFC PATCH net] ethtool: Fix incompatibility between netlink and ioctl interfaces

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Message-ID: <20200930204530.3xu7trqxu7su5vi7@lion.mk-sys.cz>
Date:   Wed, 30 Sep 2020 22:45:30 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        f.fainelli@...il.com, andrew@...n.ch, ayal@...dia.com,
        danieller@...dia.com, amcohen@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH net] ethtool: Fix incompatibility between netlink and
 ioctl interfaces

On Wed, Sep 30, 2020 at 11:06:53PM +0300, Ido Schimmel wrote:
> On Wed, Sep 30, 2020 at 10:59:17AM +0200, Michal Kubecek wrote:
> > How about this compromise? Let's introduce a "legacy" flag which would
> > allow "ethtool -s <dev> autoneg on" do what it used to do while we would
> > not taint the kernel-userspace API with this special case so that
> > ETHTOOL_MSG_LINKMODES_SET request with only ETHTOOL_A_LINKMODES_AUTONEG
> > (but no other attributes like _SPEED or _DUPLEX) would leave advertised
> > link modes untouched unless the "legacy" flag is set. If the "legacy"
> > flag is set in the request, such request would set advertised modes to
> > all supported.
> 
> Sorry for the delay, busy with other obligations. Regarding the "legacy"
> flag suggestion, do you mean that the ethtool user space utility will
> always set it in ETHTOOL_MSG_LINKMODES_SET request in order to maintain
> backward compatibility with the ioctl interface?

Yes, that is what I meant. We could also do the opposite (ioctl
compatibility by default and a flag for the way it works now) but
I would prefer the default (on userspace-kernel API level) to be "only
ETHTOOL_A_LINKMODES_AUTONEG attribute means we only want to switch
autonegotiation and touch nothing else".

Michal