Re: [PATCH net-next v3 4/5] ip_tunnel: constify input argument of ip_tunnel_info_opts( )

[Gavin Li]

On 2/20/2023 4:46 AM, Simon Horman wrote:
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>
> On Sun, Feb 19, 2023 at 09:29:21PM +0100, Simon Horman wrote:
> > On Fri, Feb 17, 2023 at 05:39:24AM +0200, Gavin Li wrote:
> > > Constify input argument(i.e. struct ip_tunnel_info *info) of
> > > ip_tunnel_info_opts( ) so that it wouldn't be needed to W/A it each time
> > > in each driver.
> > >
> > > Signed-off-by: Gavin Li <gavinl@xxxxxxxxxx>
> > > ---
> > >   include/net/ip_tunnels.h | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
> > > index fca357679816..32c77f149c6e 100644
> > > --- a/include/net/ip_tunnels.h
> > > +++ b/include/net/ip_tunnels.h
> > > @@ -485,9 +485,9 @@ static inline void iptunnel_xmit_stats(struct net_device *dev, int pkt_len)
> > >      }
> > >   }
> > >
> > > -static inline void *ip_tunnel_info_opts(struct ip_tunnel_info *info)
> > > +static inline void *ip_tunnel_info_opts(const struct ip_tunnel_info *info)
> > >   {
> > > -   return info + 1;
> > > +   return (void *)(info + 1);
> > I'm unclear on what problem this is trying to solve,
> > but info being const, and then returning (info +1)
> > as non-const feels like it is masking rather than fixing a problem.
> I now see that an example of the problem is added by path 5/5.
>
> ...
>    CC [M]  drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun_vxlan.o
> drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun_vxlan.c: In function 'mlx5e_gen_ip_tunnel_header_vxlan':
> drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun_vxlan.c:103:43: error: passing argument 1 of 'ip_tunnel_info_opts' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
>    103 |                 md = ip_tunnel_info_opts(e->tun_info);
>        |                                          ~^~~~~~~~~~
> In file included from drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun_vxlan.c:4:
> ./include/net/ip_tunnels.h:488:64: note: expected 'struct ip_tunnel_info *' but argument is of type 'const struct ip_tunnel_info *'
>    488 | static inline void *ip_tunnel_info_opts(struct ip_tunnel_info *info)
>        |                                         ~~~~~~~~~~~~~~~~~~~~~~~^~~~
> ...
>
> But I really do wonder if this patch masks rather than fixes the problem.
Hi Olek, any comment?
> > >   }
> > >
> > >   static inline void ip_tunnel_info_opts_get(void *to,
> > > --
> > > 2.31.1