linux-kernel - Re: [PATCH net-next v3 4/5] ip_tunnel: constify input argument of ip_tunnel_info

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Message-ID: <7b791f3d-6ddf-fbd4-6b09-daf1833a06fe@nvidia.com>
Date:   Wed, 22 Feb 2023 10:47:35 +0800
From:   Gavin Li <gavinl@...dia.com>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, roopa@...dia.com,
        eng.alaamohamedsoliman.am@...il.com, bigeasy@...utronix.de,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        gavi@...dia.com, roid@...dia.com, maord@...dia.com,
        saeedm@...dia.com
Subject: Re: [PATCH net-next v3 4/5] ip_tunnel: constify input argument of
 ip_tunnel_info_opts( )


On 2/20/2023 4:46 AM, Simon Horman wrote:
> External email: Use caution opening links or attachments
>
>
> 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@...dia.com>
>>> ---
>>>   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.
ACK
>
>>>   }
>>>
>>>   static inline void ip_tunnel_info_opts_get(void *to,
>>> --
>>> 2.31.1
>>>