Re: [PATCH net-next v1 3/3] net/mlx5e: TC, Add support for VxLAN GBP encap/decap flows offload

[Gavin Li]

On 2/16/2023 11:19 PM, Alexander Lobakin wrote:
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>
> From: Gavin Li <gavinl@xxxxxxxxxx>
> Date: Thu, 16 Feb 2023 16:40:33 +0800
>
> > On 2/16/2023 1:01 AM, Alexander Lobakin wrote:
> > > External email: Use caution opening links or attachments
> > >
> > >
> > > From: Gavin Li <gavinl@xxxxxxxxxx>
> > > Date: Wed, 15 Feb 2023 16:30:04 +0800
> > >
> > > > On 2/15/2023 11:36 AM, Gavin Li wrote:
> > > > > External email: Use caution opening links or attachments
> > > > >
> > > > >
> > > > > On 2/14/2023 11:26 PM, Alexander Lobakin wrote:
> > > > > > External email: Use caution opening links or attachments
> > > > > >
> > > > > >
> > > > > > From: Gavin Li <gavinl@xxxxxxxxxx>
> > > > > > Date: Tue, 14 Feb 2023 15:41:37 +0200
> > > [...]
> > >
> > > > > > > @@ -96,6 +99,70 @@ static int mlx5e_gen_ip_tunnel_header_vxlan(char
> > > > > > > buf[],
> > > > > > >          udp->dest = tun_key->tp_dst;
> > > > > > >          vxh->vx_flags = VXLAN_HF_VNI;
> > > > > > >          vxh->vx_vni = vxlan_vni_field(tun_id);
> > > > > > > +     if (tun_key->tun_flags & TUNNEL_VXLAN_OPT) {
> > > > > > > +             md = ip_tunnel_info_opts((struct ip_tunnel_info
> > > > > > > *)e->tun_info);
> > > > > > > +             vxlan_build_gbp_hdr(vxh, tun_key->tun_flags,
> > > > > > > +                                 (struct vxlan_metadata *)md);
> > > > > > Maybe constify both ip_tunnel_info_opts() and vxlan_build_gbp_hdr()
> > > > > > arguments instead of working around by casting away?
> > > > > ACK. Sorry for the confusion---I misunderstood the comment.
> > > > This ip_tunnel_info_opts is tricky to use const to annotate the arg
> > > > because it will have to cast from const to non-const again upon
> > > > returning.
> > > It's okay to cast away for the `void *` returned.
> > > Alternatively, use can convert it to a macro and use
> > > __builtin_choose_expr() or _Generic to return const or non-const
> > > depending on whether the argument is constant. That's what was recently
> > > done for container_of() IIRC.
> > I've fixed vxlan_build_gbp_hdr in V2. For ip_tunnel_info_opts, it's
> > confusing to me.
> >
> > It would be as below after constifying the parameter.
> >
> > static inline void *ip_tunnel_info_opts(const struct ip_tunnel_info *info)
> > {
> >      return (void *)(info + 1);
> > }
> > Is there any value gained by this change?
> You wouldn't need to W/A it each time in each driver, just do it once in
> the inline itself.
> I did it once in __skb_header_pointer()[0] to be able to pass data
> pointer as const to optimize code a bit and point out explicitly that
> the function doesn't modify the packet anyhow, don't see any reason to
> not do the same here.
> Or, as I said, you can use macros + __builtin_choose_expr() or _Generic.
> container_of_const() uses the latter[1]. A __builtin_choose_expr()
> variant could rely on the __same_type() macro to check whether the
> pointer passed from the driver const or not.
ACK
> > > > > > > +     }
> > > > > > > +
> > > > > > > +     return 0;
> > > > > > > +}
> > > [...]
> > >
> > > Thanks,
> > > Olek
> [0]
> https://elixir.bootlin.com/linux/v6.2-rc8/source/include/linux/skbuff.h#L3992
> [1]
> https://elixir.bootlin.com/linux/v6.2-rc8/source/include/linux/container_of.h#L33
>
> Thanks,
> Olek