netdev - Re: [PATCH v2 net] net/sched: act_mpls: Add softdep on mpls

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Date:   Wed, 28 Oct 2020 22:45:04 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Alexander Ovechkin <ovov@...dex-team.ru>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH v2 net] net/sched: act_mpls: Add softdep on mpls_gso.ko

On Wed, Oct 28, 2020 at 12:35:17PM -0700, Cong Wang wrote:
> On Tue, Oct 27, 2020 at 2:39 PM Guillaume Nault <gnault@...hat.com> wrote:
> >
> > On Tue, Oct 27, 2020 at 10:28:29AM -0700, Cong Wang wrote:
> > > On Mon, Oct 26, 2020 at 4:23 AM Guillaume Nault <gnault@...hat.com> wrote:
> > > >
> > > > TCA_MPLS_ACT_PUSH and TCA_MPLS_ACT_MAC_PUSH might be used on gso
> > > > packets. Such packets will thus require mpls_gso.ko for segmentation.
> > >
> > > Any reason not to call request_module() at run time?
> >
> > So that mpls_gso would be loaded only when initialising the
> > TCA_MPLS_ACT_PUSH or TCA_MPLS_ACT_MAC_PUSH modes?
> 
> Yes, exactly.
> 
> >
> > That could be done, but the dependency on mpls_gso wouldn't be visible
> > anymore with modinfo. I don't really mind, I just felt that such
> > information could be important for the end user.
> 
> I think the dependency is determined at run time based on
> TCA_MPLS_ACT_*, so it should be reflected at run time, rather than at
> compile time.
> 
> If loading mpls_gso even when not needed is not a big deal, I am fine
> with your patch too.

Loading mpls_gso looks harmless. It just registers GSO handlers for
ETH_P_MPLS_UC and for ETH_P_MPLS_MC with a low priority.

Since we're not adding a build dependency on mpls_gso for act_mpls, I
have a slight preference for having the soft dependency being reported
by modinfo. This gives a chance to the user to figure out that mpls_gso
can be necessary.

> Thanks.
>